Table of Contents
*****************

Gforth
1 Goals of Gforth
  1.1 Stability Goals
2 Gforth Environment
  2.1 Invoking Gforth
  2.2 Leaving Gforth
  2.3 Help on Gforth
  2.4 Command-line editing
  2.5 Environment variables
  2.6 Gforth files
  2.7 Gforth in pipes
  2.8 Startup speed
3 Forth Tutorial
  3.1 Starting Gforth
  3.2 Syntax
  3.3 Crash Course
  3.4 Stack
  3.5 Arithmetics
  3.6 Stack Manipulation
  3.7 Using files for Forth code
  3.8 Comments
  3.9 Colon Definitions
  3.10 Decompilation
  3.11 Stack-Effect Comments
  3.12 Types
  3.13 Factoring
  3.14 Designing the stack effect
  3.15 Local Variables
  3.16 Conditional execution
  3.17 Flags and Comparisons
  3.18 General Loops
  3.19 Counted loops
  3.20 Recursion
  3.21 Leaving definitions or loops
  3.22 Return Stack
  3.23 Memory
  3.24 Characters and Strings
  3.25 Alignment
  3.26 Floating Point
  3.27 Files
    3.27.1 Open file for input
    3.27.2 Create file for output
    3.27.3 Scan file for a particular line
    3.27.4 Copy input to output
    3.27.5 Close files
  3.28 Interpretation and Compilation Semantics and Immediacy
  3.29 Execution Tokens
  3.30 Exceptions
  3.31 Defining Words
  3.32 Arrays and Records
  3.33 'POSTPONE'
  3.34 'Literal'
  3.35 Advanced macros
  3.36 Compilation Tokens
  3.37 Wordlists and Search Order
4 An Introduction to Standard Forth
  4.1 Introducing the Text Interpreter
  4.2 Stacks, postfix notation and parameter passing
  4.3 Your first Forth definition
  4.4 How does that work?
  4.5 Forth is written in Forth
  4.6 Review - elements of a Forth system
  4.7 Where To Go Next
  4.8 Exercises
5 Literals in source code
6 Forth Words
  6.1 Notation
  6.2 Case insensitivity
  6.3 Comments
  6.4 Boolean Flags
  6.5 Arithmetic
    6.5.1 Single precision
    6.5.2 Double precision
    6.5.3 Mixed precision
    6.5.4 Integer division
    6.5.5 Two-stage integer division
    6.5.6 Bitwise operations
    6.5.7 Numeric comparison
    6.5.8 Floating Point
  6.6 Stack Manipulation
    6.6.1 Data stack
    6.6.2 Floating point stack
    6.6.3 Return stack
    6.6.4 Locals stack
    6.6.5 Stack pointer manipulation
  6.7 Memory
    6.7.1 Memory model
    6.7.2 Dictionary allocation
    6.7.3 Heap allocation
    6.7.4 Memory Access
    6.7.5 Special Memory Accesses
    6.7.6 Address arithmetic
    6.7.7 Memory Blocks
  6.8 Strings and Characters
    6.8.1 Characters
    6.8.2 String representations
    6.8.3 String and Character literals
    6.8.4 String words
    6.8.5 $tring words
    6.8.6 Counted string words
  6.9 Control Structures
    6.9.1 Selection
    6.9.2 Simple Loops
    6.9.3 Counted Loops
    6.9.4 'Begin' loops with multiple exits
    6.9.5 General control structures with 'case'
    6.9.6 Arbitrary control structures
      6.9.6.1 Programming Style
    6.9.7 Calls and returns
    6.9.8 Exception Handling
  6.10 Defining Words
    6.10.1 'CREATE'
    6.10.2 Variables
    6.10.3 Constants
    6.10.4 Values
    6.10.5 Varues
    6.10.6 Colon Definitions
    6.10.7 Anonymous Definitions
    6.10.8 Quotations
    6.10.9 Supplying the name of a defined word
    6.10.10 User-defined Defining Words
      6.10.10.1 User-defined defining words with colon definitions
      6.10.10.2 User-defined defining words using create
      6.10.10.3 Applications of 'CREATE..DOES>'
      6.10.10.4 The gory details of 'CREATE..DOES>'
      6.10.10.5 Advanced does> usage example
      6.10.10.6 User-defined 'to' and 'defer@'
      6.10.10.7 User-defined 'compile,'
      6.10.10.8 Creating from a prototype
      6.10.10.9 Making a word current
      6.10.10.10 'Const-does>'
    6.10.11 Deferred Words
    6.10.12 Forward
    6.10.13 Aliases
  6.11 Interpretation and Compilation Semantics
    6.11.1 Combined Words
  6.12 Tokens for Words
    6.12.1 Execution token
    6.12.2 Name token
    6.12.3 Compilation token
  6.13 Compiling words
    6.13.1 Literals
    6.13.2 Macros
  6.14 The Text Interpreter
    6.14.1 Input Sources
    6.14.2 Number Conversion
    6.14.3 Interpret/Compile states
    6.14.4 Interpreter Directives
    6.14.5 Recognizers
      6.14.5.1 Default Recognizers
      6.14.5.2 Dealing with existing Recognizers
      6.14.5.3 Defining Recognizers
    6.14.6 Text Interpreter Hooks
  6.15 The Input Stream
  6.16 Word Lists
    6.16.1 Vocabularies
    6.16.2 Why use word lists?
    6.16.3 Word list example
  6.17 Environmental Queries
  6.18 Files
    6.18.1 Forth source files
    6.18.2 General files
    6.18.3 Redirection
    6.18.4 Directories
    6.18.5 Search Paths
      6.18.5.1 Source Search Paths
      6.18.5.2 General Search Paths
  6.19 Blocks
  6.20 Other I/O
    6.20.1 Simple numeric output
    6.20.2 Formatted numeric output
    6.20.3 Floating-point output
    6.20.4 Miscellaneous output
    6.20.5 Displaying characters and strings
    6.20.6 Terminal output
      6.20.6.1 Color output
      6.20.6.2 Color themes
    6.20.7 Single-key input
    6.20.8 Line input and conversion
    6.20.9 Pipes
    6.20.10 Xchars and Unicode
    6.20.11 Internationalization and Localization
    6.20.12 Substitute
    6.20.13 CSV Reader
  6.21 OS command line arguments
  6.22 Locals
    6.22.1 Gforth locals
      6.22.1.1 Locals definitions words
      6.22.1.2 Where are locals visible by name?
      6.22.1.3 How long do locals live?
      6.22.1.4 Locals programming style
      6.22.1.5 Locals implementation
      6.22.1.6 Closures
    6.22.2 Standard Forth locals
  6.23 Structures
    6.23.1 Why explicit structure support?
    6.23.2 Structure Usage
    6.23.3 Structure Naming Convention
    6.23.4 Structure Implementation
    6.23.5 Structure Glossary
    6.23.6 Forth200x Structures
  6.24 Object-oriented Forth
    6.24.1 Why object-oriented programming?
    6.24.2 Object-Oriented Terminology
    6.24.3 The 'objects.fs' model
      6.24.3.1 Properties of the 'objects.fs' model
      6.24.3.2 Basic 'objects.fs' Usage
      6.24.3.3 The 'object.fs' base class
      6.24.3.4 Creating objects
      6.24.3.5 Object-Oriented Programming Style
      6.24.3.6 Class Binding
      6.24.3.7 Method conveniences
      6.24.3.8 Classes and Scoping
      6.24.3.9 Dividing classes
      6.24.3.10 Object Interfaces
      6.24.3.11 'objects.fs' Implementation
      6.24.3.12 'objects.fs' Glossary
    6.24.4 The 'oof.fs' model
      6.24.4.1 Properties of the 'oof.fs' model
      6.24.4.2 Basic 'oof.fs' Usage
      6.24.4.3 The 'oof.fs' base class
      6.24.4.4 Class Declaration
      6.24.4.5 Class Implementation
    6.24.5 The 'mini-oof.fs' model
      6.24.5.1 Basic 'mini-oof.fs' Usage
      6.24.5.2 Mini-OOF Example
      6.24.5.3 'mini-oof.fs' Implementation
    6.24.6 Mini-OOF2
    6.24.7 Comparison with other object models
  6.25 Regular Expressions
  6.26 Programming Tools
    6.26.1 Locating source code definitions
    6.26.2 Locating uses of a word
    6.26.3 Locating exception source
    6.26.4 Examining compiled code
    6.26.5 Examining data and code
    6.26.6 Forgetting words
    6.26.7 Debugging
    6.26.8 Assertions
    6.26.9 Singlestep Debugger
    6.26.10 Code Coverage and Execution Frequency
  6.27 Multitasker
    6.27.1 Pthreads
      6.27.1.1 Basic multi-tasking
      6.27.1.2 Task-local data
      6.27.1.3 Semaphores
      6.27.1.4 Hardware operations for multi-tasking
      6.27.1.5 Message queues
    6.27.2 Cilk
  6.28 C Interface
    6.28.1 Calling C functions
    6.28.2 Declaring C Functions
    6.28.3 Calling C function pointers from Forth
    6.28.4 Defining library interfaces
    6.28.5 Declaring OS-level libraries
    6.28.6 Callbacks
    6.28.7 How the C interface works
    6.28.8 Low-Level C Interface Words
    6.28.9 Automated interface generation using SWIG
      6.28.9.1 Basic operation
      6.28.9.2 Detailed operation:
      6.28.9.3 Examples
    6.28.10 Migrating from Gforth 0.7
  6.29 Assembler and Code Words
    6.29.1 Definitions in assembly language
    6.29.2 Common Assembler
    6.29.3 Common Disassembler
    6.29.4 386 Assembler
    6.29.5 AMD64 (x86_64) Assembler
    6.29.6 Alpha Assembler
    6.29.7 MIPS assembler
    6.29.8 PowerPC assembler
    6.29.9 ARM Assembler
    6.29.10 Other assemblers
  6.30 Carnal words
    6.30.1 Header fields
    6.30.2 Header methods
    6.30.3 Threading Words
  6.31 Passing Commands to the Operating System
  6.32 Keeping track of Time
  6.33 Miscellaneous Words
7 Error messages
8 Tools
  8.1 'ans-report.fs': Report the words used, sorted by wordset
    8.1.1 Caveats
  8.2 Stack depth changes during interpretation
9 Standard conformance
  9.1 The Core Words
    9.1.1 Implementation Defined Options
    9.1.2 Ambiguous conditions
    9.1.3 Other system documentation
  9.2 The optional Block word set
    9.2.1 Implementation Defined Options
    9.2.2 Ambiguous conditions
    9.2.3 Other system documentation
  9.3 The optional Double Number word set
    9.3.1 Ambiguous conditions
  9.4 The optional Exception word set
    9.4.1 Implementation Defined Options
  9.5 The optional Facility word set
    9.5.1 Implementation Defined Options
    9.5.2 Ambiguous conditions
  9.6 The optional File-Access word set
    9.6.1 Implementation Defined Options
    9.6.2 Ambiguous conditions
  9.7 The optional Floating-Point word set
    9.7.1 Implementation Defined Options
    9.7.2 Ambiguous conditions
  9.8 The optional Locals word set
    9.8.1 Implementation Defined Options
    9.8.2 Ambiguous conditions
  9.9 The optional Memory-Allocation word set
    9.9.1 Implementation Defined Options
  9.10 The optional Programming-Tools word set
    9.10.1 Implementation Defined Options
    9.10.2 Ambiguous conditions
  9.11 The optional Search-Order word set
    9.11.1 Implementation Defined Options
    9.11.2 Ambiguous conditions
10 Should I use Gforth extensions?
11 Model
12 Integrating Gforth into C programs
  12.1 Types
  12.2 Variables
  12.3 Functions
  12.4 Signals
13 Emacs and Gforth
  13.1 Installing gforth.el
  13.2 Emacs Tags
  13.3 Hilighting
  13.4 Auto-Indentation
  13.5 Blocks Files
14 Image Files
  14.1 Image Licensing Issues
  14.2 Image File Background
  14.3 Non-Relocatable Image Files
  14.4 Data-Relocatable Image Files
  14.5 Fully Relocatable Image Files
    14.5.1 'gforthmi'
    14.5.2 'cross.fs'
  14.6 Stack and Dictionary Sizes
  14.7 Running Image Files
  14.8 Modifying the Startup Sequence
15 Engine
  15.1 Portability
  15.2 Threading
    15.2.1 Scheduling
    15.2.2 Direct or Indirect Threaded?
    15.2.3 Dynamic Superinstructions
    15.2.4 DOES>
  15.3 Primitives
    15.3.1 Automatic Generation
    15.3.2 TOS Optimization
    15.3.3 Produced code
  15.4 Performance
16 Cross Compiler
  16.1 Using the Cross Compiler
  16.2 How the Cross Compiler Works
17 MINOS2, a GUI library
  17.1 MINOS2 object framework
    17.1.1 'actor' methods:
    17.1.2 'widget' methods:
  17.2 MINOS2 tutorial
Appendix A Bugs
Appendix B Authors and Ancestors of Gforth
  B.1 Authors and Contributors
  B.2 Pedigree
Appendix C Other Forth-related information
Appendix D Licenses
  D.1 GNU Free Documentation License
    D.1.1 ADDENDUM: How to use this License for your documents
  D.2 GNU GENERAL PUBLIC LICENSE
Word Index
Concept and Word Index
Gforth
******

This manual is for Gforth (version 0.7.9_20240306, March 06, 2024), a
fast and portable implementation of the Standard Forth language.  It
serves as reference manual, but it also contains an introduction to
Forth and a Forth tutorial.

   Authors: Bernd Paysan, Anton Ertl, Gerald Wodni Copyright © 1995,
1996, 1997, 1998, 2000, 2003, 2004, 2005, 2006, 2007, 2008, 2009, 2010,
2011, 2012, 2013, 2014,2015,2016,2017,2018,2019,2020,2021,2022,2023 Free
Software Foundation, Inc.

     Permission is granted to copy, distribute and/or modify this
     document under the terms of the GNU Free Documentation License,
     Version 1.1 or any later version published by the Free Software
     Foundation; with no Invariant Sections, with the Front-Cover texts
     being "A GNU Manual," and with the Back-Cover Texts as in (a)
     below.  A copy of the license is included in the section entitled
     "GNU Free Documentation License."

     (a) The FSF's Back-Cover Text is: "You have freedom to copy and
     modify this GNU Manual, like GNU software.  Copies published by the
     Free Software Foundation raise funds for GNU development."

1 Goals of Gforth
*****************

The goal of the Gforth Project is to develop a standard model for
Standard Forth.  This can be split into several subgoals:

   * Gforth should conform to the Forth Standard.
   * It should be a model, i.e.  it should define all the
     implementation-dependent things.
   * It should become standard, i.e.  widely accepted and used.  This
     goal is the most difficult one.

   To achieve these goals Gforth should be
   * Similar to previous models (fig-Forth, F83)
   * Powerful.  It should provide for all the things that are considered
     necessary today and even some that are not yet considered
     necessary.
   * Efficient.  It should not get the reputation of being exceptionally
     slow.
   * Free.
   * Available on many machines/easy to port.

   Have we achieved these goals?  Gforth conforms to the Forth-94 (ANS
Forth) and Forth-2012 standards.  We have changed some of the internal
data structures (in particular, the headers) over time, so Gforth cannot
be considered a stable model.  It certainly has not yet become a de
facto standard, but it appears to be quite popular.  It has some
similarities to and some differences from previous models.  It has some
powerful features, but not yet everything that we envisioned.  We
certainly have achieved our execution speed goals (*note
Performance::)(1).  It is free and available on many machines.

   ---------- Footnotes ----------

   (1) However, in 1998 the bar was raised when the major commercial
Forth vendors switched to native code compilers.

1.1 Stability Goals
===================

Programs that work on earlier versions of Gforth should also work on
newer versions.  However, there are some caveats:

   Internal data structures (including the representation of code) of
Gforth may change between versions, unless they are documented.

   Moreover, we only feel obliged to keep standard words (i.e., with
standard wordset names) and words documented as permanent Gforth
extensions (with wordset name 'gforth' or 'gforth-<version>', *note
Notation::).  Other words may be removed in newer releases.

   In particular, you may find a word by using 'locate' or otherwise
inspecting Gforth's source code.  You can see the wordset in a comment
right after the stack-effect comment.  If there is no wordset for a
word, it is an internal factor and may be removed in a future version.
If the wordset is 'gforth-experimental', 'gforth-internal', or
'gforth-obsolete', the word may also be removed in a future version.

   If you want to use a particular word that is not marked as permanent,
please let us know, and we will consider to add the word as permanent
word (or we may suggest an alternative to using this word).

2 Gforth Environment
********************

Note: ultimately, the Gforth man page will be auto-generated from the
material in this chapter.

   For related information about the creation of images see *note Image
Files::.

2.1 Invoking Gforth
===================

Gforth is made up of two parts; an executable "engine" (named 'gforth'
or 'gforth-fast') and an image file.  To start it, you will usually just
say 'gforth' -- this automatically loads the default image file
'gforth.fi'.  In many other cases the default Gforth image will be
invoked like this:
     gforth [file | -e forth-code] ...
This interprets the contents of the files and the Forth code in the
order they are given.

   In addition to the 'gforth' engine, there is also an engine called
'gforth-fast', which is faster, but gives less informative error
messages (*note Error messages::) and may catch some errors (in
particular, stack underflows and integer division errors) later or not
at all.  You should use it for debugged, performance-critical programs.

   Moreover, there is an engine called 'gforth-itc', which is useful in
some backwards-compatibility situations (*note Direct or Indirect
Threaded?::).

   In general, the command line looks like this:

     gforth[-fast] [engine options] [image options]

   The engine options must come before the rest of the command line.
They are:

'--image-file file'
'-i file'
     Loads the Forth image file instead of the default 'gforth.fi'
     (*note Image Files::).

'--appl-image file'
     Loads the image file and leaves all further command-line arguments
     to the image (instead of processing them as engine options).  This
     is useful for building executable application images on Unix, built
     with 'gforthmi --application ...'.

'--path path'
'-p path'
     Uses path for searching the image file and Forth source code files
     instead of the default in the environment variable 'GFORTHPATH' or
     the path specified at installation time and the working directory
     '.' (e.g., '/usr/local/share/gforth/0.2.0:.').  A path is given as
     a list of directories, separated by ':' (previous versions had ';'
     for other OSes, but since Cygwin now only accepts
     '/cygdrive/<letter>', and we dropped support for OS/2 and MS-DOS,
     it is ':' everywhere).

'--dictionary-size size'
'-m size'
     Allocate size space for the Forth dictionary space instead of using
     the default specified in the image (typically 256K). The size
     specification for this and subsequent options consists of an
     integer and a unit (e.g., '4M').  The unit can be one of 'b'
     (bytes), 'e' (element size, in this case Cells), 'k' (kilobytes),
     'M' (Megabytes), 'G' (Gigabytes), and 'T' (Terabytes).  If no unit
     is specified, 'e' is used.

'--data-stack-size size'
'-d size'
     Allocate size space for the data stack instead of using the default
     specified in the image (typically 16K).

'--return-stack-size size'
'-r size'
     Allocate size space for the return stack instead of using the
     default specified in the image (typically 15K).

'--fp-stack-size size'
'-f size'
     Allocate size space for the floating point stack instead of using
     the default specified in the image (typically 15.5K). In this case
     the unit specifier 'e' refers to floating point numbers.

'--locals-stack-size size'
'-l size'
     Allocate size space for the locals stack instead of using the
     default specified in the image (typically 14.5K).

'--vm-commit'
     Normally, Gforth tries to start up even if there is not enough
     virtual memory for the dictionary and the stacks (using
     'MAP_NORESERVE' on OSs that support it); so you can ask for a
     really big dictionary and/or stacks, and as long as you don't use
     more virtual memory than is available, everything will be fine (but
     if you use more, processes get killed).  With this option you just
     use the default allocation policy of the OS; for OSs that don't
     overcommit (e.g., Solaris), this means that you cannot and should
     not ask for as big dictionary and stacks, but once Gforth
     successfully starts up, out-of-memory won't kill it.

'--help'
'-h'
     Print a message about the command-line options

'--version'
'-v'
     Print version and exit

'--debug'
     Print some information useful for debugging on startup.

'--offset-image'
     Start the dictionary at a slightly different position than would be
     used otherwise (useful for creating data-relocatable images, *note
     Data-Relocatable Image Files::).

'--no-offset-im'
     Start the dictionary at the normal position.

'--clear-dictionary'
     Initialize all bytes in the dictionary to 0 before loading the
     image (*note Data-Relocatable Image Files::).

'--die-on-signal'
     Normally Gforth handles most signals (e.g., the user interrupt
     SIGINT, or the segmentation violation SIGSEGV) by translating it
     into a Forth 'THROW'.  With this option, Gforth exits if it
     receives such a signal.  This option is useful when the engine
     and/or the image might be severely broken (such that it causes
     another signal before recovering from the first); this option
     avoids endless loops in such cases.

'--no-dynamic'
'--dynamic'
     Disable or enable dynamic superinstructions with replication (*note
     Dynamic Superinstructions::).

'--no-super'
     Disable dynamic superinstructions, use just dynamic replication;
     this is useful if you want to patch threaded code (*note Dynamic
     Superinstructions::).

'--ss-number=N'
     Use only the first N static superinstructions compiled into the
     engine (default: use them all; note that only 'gforth-fast' has
     any).  This option is useful for measuring the performance impact
     of static superinstructions.

'--ss-min-codesize'
'--ss-min-ls'
'--ss-min-lsu'
'--ss-min-nexts'
     Use specified metric for determining the cost of a primitive or
     static superinstruction for static superinstruction selection.
     'Codesize' is the native code size of the primive or static
     superinstruction, 'ls' is the number of loads and stores, 'lsu' is
     the number of loads, stores, and updates, and 'nexts' is the number
     of dispatches (not taking dynamic superinstructions into account),
     i.e.  every primitive or static superinstruction has cost 1.
     Default: 'codesize' if you use dynamic code generation, otherwise
     'nexts'.

'--ss-greedy'
     This option is useful for measuring the performance impact of
     static superinstructions.  By default, an optimal shortest-path
     algorithm is used for selecting static superinstructions.  With
     '--ss-greedy' this algorithm is modified to assume that anything
     after the static superinstruction currently under consideration is
     not combined into static superinstructions.  With '--ss-min-nexts'
     this produces the same result as a greedy algorithm that always
     selects the longest superinstruction available at the moment.
     E.g., if there are superinstructions AB and BCD, then for the
     sequence A B C D the optimal algorithm will select A BCD and the
     greedy algorithm will select AB C D.

'--print-metrics'
     Prints some metrics used during static superinstruction selection:
     'code size' is the actual size of the dynamically generated code.
     'Metric codesize' is the sum of the codesize metrics as seen by
     static superinstruction selection; there is a difference from 'code
     size', because not all primitives and static superinstructions are
     compiled into dynamically generated code, and because of markers.
     The other metrics correspond to the 'ss-min-...' options.  This
     option is useful for evaluating the effects of the '--ss-...'
     options.

   As explained above, the image-specific command-line arguments for the
default image 'gforth.fi' consist of a sequence of filenames and '-e
FORTH-CODE' options that are interpreted in the sequence in which they
are given.  The '-e FORTH-CODE' or '--evaluate FORTH-CODE' option
evaluates the Forth code.  This option takes only one argument; if you
want to evaluate more Forth words, you have to quote them or use '-e'
several times.  To exit after processing the command line (instead of
entering interactive mode) append '-e bye' to the command line.  You can
also process the command-line arguments with a Forth program (*note OS
command line arguments::).

   If you have several versions of Gforth installed, 'gforth' will
invoke the version that was installed last.  'gforth-<version>' invokes
a specific version.  If your environment contains the variable
'GFORTHPATH', you may want to override it by using the '--path' option.

   On startup, before processing any of the image option, the user
initialization file either specified in the environment variable
'GFORTH_ENV' or, if not set, '~/.config/gforthrc0' is included, if it
exists.  If 'GFORTH_ENV' is "'off'," nothing is included.  After
processing all the image options and just before printing the boot
message, the user initialization file '~/.config/gforthrc' from your
home directory is included, unless the option '--no-rc' is given.

   Warning levels can be set with

'-W'
     Turn off warnings

'-Won'
     Turn on warnings (level 1)

'-Wall'
     Turn on beginner warnings (level 2)

'-Wpedantic'
     Turn on pedantic warnings (level 3)

'-Werror'
     Turn warnings into errors (level 4)

2.2 Leaving Gforth
==================

You can leave Gforth by typing 'bye' or 'Ctrl-d' (at the start of a
line) or (if you invoked Gforth with the '--die-on-signal' option)
'Ctrl-c'.  When you leave Gforth, all of your definitions and data are
discarded.  For ways of saving the state of the system before leaving
Gforth see *note Image Files::.

   doc-bye

2.3 Help on Gforth
==================

Gforth has a simple, text-based online help system.

'help' ( "rest-of-line" --  ) gforth-1.0 "help"
   If no name is given, show basic help.  If a documentation node name
is given followed by "::", show the start of the node.  If the name of a
word is given, show the documentation of the word if it exists, or its
source code if not.  Use 'g' to enter the editor at the point shown by
'help'.  'Help' sets the current location, so you can use 'n' and 'b' to
show more of the text, or 'g' to visit the documentation in an editor
(*note Locating source code definitions::).

'authors' ( --  ) gforth-1.0 "authors"
   show the list of authors

'license' ( --  ) gforth-0.2 "license"
   print the license statement

2.4 Command-line editing
========================

Gforth maintains a history file that records every line that you type to
the text interpreter.  This file is preserved between sessions, and is
used to provide a command-line recall facility; if you type 'Ctrl-P'
repeatedly you can recall successively older commands from this (or
previous) session(s).  The full list of command-line editing facilities
is:

   * 'Ctrl-p' ("previous") (or up-arrow) to recall successively older
     lines from the history buffer.
   * 'Ctrl-n' ("next") (or down-arrow) to recall successively newer
     lines from the history buffer.  If you moved to an older line
     earlier and gave it to Gforth for text-interpretation, asking for
     the next line as the first editing command gives you the next line
     after the one you selected last time.
   * 'Ctrl-f' (or right-arrow) to move the cursor right,
     non-destructively.
   * 'Ctrl-b' (or left-arrow) to move the cursor left,
     non-destructively.
   * 'Ctrl-h' (backspace) to delete the character to the left of the
     cursor, closing up the line.
   * 'Ctrl-k' to delete ("kill") from the cursor to the end of the line.
   * 'Ctrl-a' to move the cursor to the start of the line.
   * 'Ctrl-e' to move the cursor to the end of the line.
   * <RET> ('Ctrl-m') or <LFD> ('Ctrl-j') to submit the current line.
   * <TAB> to step through all possible full-word completions of the
     word currently being typed.
   * 'Ctrl-d' on an empty line line to terminate Gforth (gracefully,
     using 'bye').
   * 'Ctrl-x' (or 'Ctrl-d' on a non-empty line) to delete the character
     under the cursor.

   When editing, displayable characters are inserted to the left of the
cursor position; the line is always in "insert" (as opposed to
"overstrike") mode.

   On Unix systems, the history file is
'$HOME/.local/share/gforth/history' by default(1).  You can find out the
name and location of your history file using:

     history-file type \ Unix-class systems

     history-file type \ Other systems
     history-dir  type

   If you enter long definitions by hand, you can use a text editor to
paste them out of the history file into a Forth source file for reuse at
a later time.

   Gforth never trims the size of the history file, so you should do
this periodically, if necessary.

   ---------- Footnotes ----------

   (1) i.e.  it is stored in the user's home directory.

2.5 Environment variables
=========================

Gforth uses these environment variables:

   * 'GFORTHHIST' -- (Unix systems only) specifies the path for the
     history file '.gforth-history'.  Default:
     '$HOME/.local/share/gforth/history'.

   * 'GFORTHPATH' -- specifies the path used when searching for the
     gforth image file and for Forth source-code files (usually '.', the
     current working directory).  Path separator is ':', a typical path
     would be '/usr/local/share/gforth/1.0:.'.

   * 'LANG' -- see 'LC_CTYPE'

   * 'LC_ALL' -- see 'LC_CTYPE'

   * 'LC_CTYPE' -- If this variable contains "UTF-8" on Gforth startup,
     Gforth uses the UTF-8 encoding for strings internally and expects
     its input and produces its output in UTF-8 encoding, otherwise the
     encoding is 8bit (see *note Xchars and Unicode::).  If this
     environment variable is unset, Gforth looks in 'LC_ALL', and if
     that is unset, in 'LANG'.

   * 'GFORTHSYSTEMPREFIX' -- specifies what to prepend to the argument of
     'system' before passing it to C's 'system()'.  Default:
     '"./$COMSPEC /c "' on Windows, '""' on other OSs.  The prefix and
     the command are directly concatenated, so if a space between them
     is necessary, append it to the prefix.

   * 'GFORTH' -- used by 'gforthmi', *Note gforthmi::.

   * 'GFORTHD' -- used by 'gforthmi', *Note gforthmi::.

   * 'TMP', 'TEMP' - (non-Unix systems only) used as a potential
     location for the history file.

   All the Gforth environment variables default to sensible values if
they are not set.

2.6 Gforth files
================

When you install Gforth on a Unix system, it installs files in these
locations by default:

   * '/usr/local/bin/gforth'
   * '/usr/local/bin/gforthmi'
   * '/usr/local/man/man1/gforth.1' - man page.
   * '/usr/local/info' - the Info version of this manual.
   * '/usr/local/lib/gforth/<version>/...' - Gforth '.fi' files.
   * '/usr/local/share/gforth/<version>/TAGS' - Emacs TAGS file.
   * '/usr/local/share/gforth/<version>/...' - Gforth source files.
   * '.../emacs/site-lisp/gforth.el' - Emacs gforth mode.

   You can select different places for installation by using 'configure'
options (listed with 'configure --help').

2.7 Gforth in pipes
===================

Gforth can be used in pipes created elsewhere (described in the
following).  It can also create pipes on its own (*note Pipes::).

   If you pipe into Gforth, your program should read with 'read-file' or
'read-line' from 'stdin' (*note General files::).  'Key' does not
recognize the end of input.  Words like 'accept' echo the input and are
therefore usually not useful for reading from a pipe.  You have to
invoke the Forth program with an OS command-line option, as you have no
chance to use the Forth command line (the text interpreter would try to
interpret the pipe input).

   You can output to a pipe with 'type', 'emit', 'cr' etc.

   When you write to a pipe that has been closed at the other end,
Gforth receives a SIGPIPE signal ("pipe broken").  Gforth translates
this into the exception 'broken-pipe-error'.  If your application does
not catch that exception, the system catches it and exits, usually
silently (unless you were working on the Forth command line; then it
prints an error message and exits).  This is usually the desired
behaviour.

   If you do not like this behaviour, you have to catch the exception
yourself, and react to it.

   Here's an example of an invocation of Gforth that is usable in a
pipe:

     gforth -e ": foo begin pad dup 10 stdin read-file throw dup while \
      type repeat ; foo bye"

   This example just copies the input verbatim to the output.  A very
simple pipe containing this example looks like this:

     cat startup.fs |
     gforth -e ": foo begin pad dup 80 stdin read-file throw dup while \
      type repeat ; foo bye"|
     head

   Pipes involving Gforth's 'stderr' output do not work.

2.8 Startup speed
=================

If Gforth is used for CGI scripts or in shell scripts, its startup speed
may become a problem.  On a 3GHz Core 2 Duo E8400 under 64-bit Linux
2.6.27.8 with libc-2.7, 'gforth-fast -e bye' takes 13.1ms user and 1.2ms
system time ('gforth -e bye' is faster on startup with about 3.4ms user
time and 1.2ms system time, because it subsumes some of the options
discussed below).

   If startup speed is a problem, you may consider the following ways to
improve it; or you may consider ways to reduce the number of startups
(for example, by using Fast-CGI). Note that the first steps below
improve the startup time at the cost of run-time (including
compile-time), so whether they are profitable depends on the balance of
these times in your application.

   An easy step that influences Gforth startup speed is the use of a
number of options that increase run-time, but decrease image-loading
time.

   The first of these that you should try is '--ss-number=0
--ss-states=1' because this option buys relatively little run-time
speedup and costs quite a bit of time at startup.  'gforth-fast
--ss-number=0 --ss-states=1 -e bye' takes about 2.8ms user and 1.5ms
system time.

   The next option is '--no-dynamic' which has a substantial impact on
run-time (about a factor of 2 on several platforms), but still makes
startup speed a little faster: 'gforth-fast --ss-number=0 --ss-states=1
--no-dynamic -e bye' consumes about 2.6ms user and 1.2ms system time.

   The next step to improve startup speed is to use a data-relocatable
image (*note Data-Relocatable Image Files::).  This avoids the
relocation cost for the code in the image (but not for the data).  Note
that the image is then specific to the particular binary you are using
(i.e., whether it is 'gforth', 'gforth-fast', and even the particular
build).  You create the data-relocatable image that works with
'./gforth-fast' with 'GFORTHD="./gforth-fast --no-dynamic" gforthmi
gforthdr.fi' (the '--no-dynamic' is required here or the image will not
work).  And you run it with 'gforth-fast -i gforthdr.fi ... -e bye' (the
flags discussed above don't matter here, because they only come into
play on relocatable code).  'gforth-fast -i gforthdr.fi -e bye' takes
about 1.1ms user and 1.2ms system time.

   One step further is to avoid all relocation cost and part of the
copy-on-write cost through using a non-relocatable image (*note
Non-Relocatable Image Files::).  However, this has the disadvantage that
it does not work on operating systems with address space randomization
(the default in, e.g., Linux nowadays), or if the dictionary moves for
any other reason (e.g., because of a change of the OS kernel or an
updated library), so we cannot really recommend it.  You create a
non-relocatable image with 'gforth-fast --no-dynamic -e "savesystem
gforthnr.fi bye"' (the '--no-dynamic' is required here, too).  And you
run it with 'gforth-fast -i gforthnr.fi ... -e bye' (again the flags
discussed above don't matter).  'gforth-fast -i gforthdr.fi -e bye'
takes about 0.9ms user and 0.9ms system time.

   If the script you want to execute contains a significant amount of
code, it may be profitable to compile it into the image to avoid the
cost of compiling it at startup time.

3 Forth Tutorial
****************

The difference of this chapter from the Introduction (*note
Introduction::) is that this tutorial is more fast-paced, should be used
while sitting in front of a computer, and covers much more material, but
does not explain how the Forth system works.

   This tutorial can be used with any Standard-compliant Forth; any
Gforth-specific features are marked as such and you can skip them if you
work with another Forth.  This tutorial does not explain all features of
Forth, just enough to get you started and give you some ideas about the
facilities available in Forth.  Read the rest of the manual when you are
through this.

   The intended way to use this tutorial is that you work through it
while sitting in front of the console, take a look at the examples and
predict what they will do, then try them out; if the outcome is not as
expected, find out why (e.g., by trying out variations of the example),
so you understand what's going on.  There are also some assignments that
you should solve.

   This tutorial assumes that you have programmed before and know what,
e.g., a loop is.

3.1 Starting Gforth
===================

You can start Gforth by typing its name:

     gforth

   That puts you into interactive mode; you can leave Gforth by typing
'bye'.  While in Gforth, you can edit the command line and access the
command line history with cursor keys, similar to bash.

3.2 Syntax
==========

A "word" is a sequence of arbitrary characters (except white space).
Words are separated by white space.  E.g., each of the following lines
contains exactly one word:

     word
     !@#$%^&*()
     1234567890
     5!a

   A frequent beginner's error is to leave out necessary white space,
resulting in an error like 'Undefined word'; so if you see such an
error, check if you have put spaces wherever necessary.

     ." hello, world" \ correct
     ."hello, world"  \ gives an "Undefined word" error

   Gforth and most other Forth systems ignore differences in case (they
are case-insensitive), i.e., 'word' is the same as 'Word'.  If your
system is case-sensitive, you may have to type all the examples given
here in upper case.

3.3 Crash Course
================

Forth does not prevent you from shooting yourself in the foot.  Let's
try a few ways to crash Gforth:

     0 0 !
     here execute
     ' catch >body 20 erase abort
     ' (quit1) >body 20 erase

   The last two examples are guaranteed to destroy important parts of
Gforth (and most other systems), so you better leave Gforth afterwards
(if it has not finished by itself).  On some systems you may have to
kill gforth from outside (e.g., in Unix with 'kill').

   You will find out later what these lines do and then you will get an
idea why they produce crashes.

   Now that you know how to produce crashes (and that there's not much
to them), let's learn how to produce meaningful programs.

3.4 Stack
=========

The most obvious feature of Forth is the stack.  When you type in a
number, it is pushed on the stack.  You can display the contents of the
stack with '.s'.

     1 2 .s
     3 .s

   '.s' displays the top-of-stack to the right, i.e., the numbers appear
in '.s' output as they appeared in the input.

   You can print the top element of the stack with '.'.

     1 2 3 . . .

   In general, words consume their stack arguments ('.s' is an
exception).

     Assignment: What does the stack contain after '5 6 7 .'?

3.5 Arithmetics
===============

The words '+', '-', '*', '/', and 'mod' always operate on the top two
stack items:

     2 2 .s
     + .s
     .
     2 1 - .
     7 3 mod .

   The operands of '-', '/', and 'mod' are in the same order as in the
corresponding infix expression (this is generally the case in Forth).

   Parentheses are superfluous (and not available), because the order of
the words unambiguously determines the order of evaluation and the
operands:

     3 4 + 5 * .
     3 4 5 * + .

     Assignment: What are the infix expressions corresponding to the
     Forth code above?  Write '6-7*8+9' in Forth notation(1).

   To change the sign, use 'negate':

     2 negate .

     Assignment: Convert -(-3)*4-5 to Forth.

   '/mod' performs both '/' and 'mod'.

     7 3 /mod . .

   Reference: *note Arithmetic::.

   ---------- Footnotes ----------

   (1) This notation is also known as Postfix or RPN (Reverse Polish
Notation).

3.6 Stack Manipulation
======================

Stack manipulation words rearrange the data on the stack.

     1 .s drop .s
     1 .s dup .s drop drop .s
     1 2 .s over .s drop drop drop
     1 2 .s swap .s drop drop
     1 2 3 .s rot .s drop drop drop

   These are the most important stack manipulation words.  There are
also variants that manipulate twice as many stack items:

     1 2 3 4 .s 2swap .s 2drop 2drop

   Two more stack manipulation words are:

     1 2 .s nip .s drop
     1 2 .s tuck .s 2drop drop

     Assignment: Replace 'nip' and 'tuck' with combinations of other
     stack manipulation words.

          Given:          How do you get:
          1 2 3           3 2 1
          1 2 3           1 2 3 2
          1 2 3           1 2 3 3
          1 2 3           1 3 3
          1 2 3           2 1 3
          1 2 3 4         4 3 2 1
          1 2 3           1 2 3 1 2 3
          1 2 3 4         1 2 3 4 1 2
          1 2 3
          1 2 3           1 2 3 4
          1 2 3           1 3

     5 dup * .

     Assignment: Write 17^3 and 17^4 in Forth, without writing '17' more
     than once.  Write a piece of Forth code that expects two numbers on
     the stack (A and B, with B on top) and computes '(a-b)(a+1)'.

   Reference: *note Stack Manipulation::.

3.7 Using files for Forth code
==============================

While working at the Forth command line is convenient for one-line
examples and short one-off code, you probably want to store your source
code in files for convenient editing and persistence.  You can use your
favourite editor (Gforth includes Emacs support, *note Emacs and
Gforth::) to create FILE.FS and use

     s" FILE.FS" included

   to load it into your Forth system.  The file name extension I use for
Forth files is '.fs'.

   You can easily start Gforth with some files loaded like this:

     gforth FILE1.FS FILE2.FS

   If an error occurs during loading these files, Gforth terminates,
whereas an error during 'INCLUDED' within Gforth usually gives you a
Gforth command line.  Starting the Forth system every time gives you a
clean start every time, without interference from the results of earlier
tries.

   I often put all the tests in a file, then load the code and run the
tests with

     gforth CODE.FS TESTS.FS -e bye

   (often by performing this command with 'C-x C-e' in Emacs).  The '-e
bye' ensures that Gforth terminates afterwards so that I can restart
this command without ado.

   The advantage of this approach is that the tests can be repeated
easily every time the program ist changed, making it easy to catch bugs
introduced by the change.

   Reference: *note Forth source files::.

3.8 Comments
============

     \ That's a comment; it ends at the end of the line
     ( Another comment; it ends here: )  .s

   '\' and '(' are ordinary Forth words and therefore have to be
separated with white space from the following text.

     \This gives an "Undefined word" error

   The first ')' ends a comment started with '(', so you cannot nest
'('-comments; and you cannot comment out text containing a ')' with '(
... )'(1).

   I use '\'-comments for descriptive text and for commenting out code
of one or more line; I use '('-comments for describing the stack effect,
the stack contents, or for commenting out sub-line pieces of code.

   The Emacs mode 'gforth.el' (*note Emacs and Gforth::) supports these
uses by commenting out a region with 'C-x \', uncommenting a region with
'C-u C-x \', and filling a '\'-commented region with 'M-q'.

   Reference: *note Comments::.

   ---------- Footnotes ----------

   (1) therefore it's a good idea to avoid ')' in word names.

3.9 Colon Definitions
=====================

are similar to procedures and functions in other programming languages.

     : squared ( n -- n^2 )
        dup * ;
     5 squared .
     7 squared .

   ':' starts the colon definition; its name is 'squared'.  The
following comment describes its stack effect.  The words 'dup *' are not
executed, but compiled into the definition.  ';' ends the colon
definition.

   The newly-defined word can be used like any other word, including
using it in other definitions:

     : cubed ( n -- n^3 )
        dup squared * ;
     -5 cubed .
     : fourth-power ( n -- n^4 )
        squared squared ;
     3 fourth-power .

     Assignment: Write colon definitions for 'nip', 'tuck', 'negate',
     and '/mod' in terms of other Forth words, and check if they work
     (hint: test your tests on the originals first).  Don't let the
     'redefined'-Messages spook you, they are just warnings.

   Reference: *note Colon Definitions::.

3.10 Decompilation
==================

You can decompile colon definitions with 'see':

     see squared
     see cubed

   In Gforth 'see' shows you a reconstruction of the source code from
the executable code.  Informations that were present in the source, but
not in the executable code, are lost (e.g., comments).

   You can also decompile the predefined words:

     see .
     see +

3.11 Stack-Effect Comments
==========================

By convention the comment after the name of a definition describes the
stack effect: The part in front of the '--' describes the state of the
stack before the execution of the definition, i.e., the parameters that
are passed into the colon definition; the part behind the '--' is the
state of the stack after the execution of the definition, i.e., the
results of the definition.  The stack comment only shows the top stack
items that the definition accesses and/or changes.

   You should put a correct stack effect on every definition, even if it
is just '( -- )'.  You should also add some descriptive comment to more
complicated words (I usually do this in the lines following ':').  If
you don't do this, your code becomes unreadable (because you have to
work through every definition before you can understand any).

     Assignment: The stack effect of 'swap' can be written like this:
     'x1 x2 -- x2 x1'.  Describe the stack effect of '-', 'drop', 'dup',
     'over', 'rot', 'nip', and 'tuck'.  Hint: When you are done, you can
     compare your stack effects to those in this manual (*note Word
     Index::).

   Sometimes programmers put comments at various places in colon
definitions that describe the contents of the stack at that place (stack
comments); i.e., they are like the first part of a stack-effect comment.
E.g.,

     : cubed ( n -- n^3 )
        dup squared  ( n n^2 ) * ;

   In this case the stack comment is pretty superfluous, because the
word is simple enough.  If you think it would be a good idea to add such
a comment to increase readability, you should also consider factoring
the word into several simpler words (*note Factoring: Factoring
Tutorial.), which typically eliminates the need for the stack comment;
however, if you decide not to refactor it, then having such a comment is
better than not having it.

   The names of the stack items in stack-effect and stack comments in
the standard, in this manual, and in many programs specify the type
through a type prefix, similar to Fortran and Hungarian notation.  The
most frequent prefixes are:

'n'
     signed integer
'u'
     unsigned integer
'c'
     character
'f'
     Boolean flags, i.e.  'false' or 'true'.
'a-addr,a-'
     Cell-aligned address
'c-addr,c-'
     Char-aligned address (note that a Char may have two bytes in
     Windows NT)
'xt'
     Execution token, same size as Cell
'w,x'
     Cell, can contain an integer or an address.  It usually takes 32,
     64 or 16 bits (depending on your platform and Forth system).  A
     cell is more commonly known as machine word, but the term _word_
     already means something different in Forth.
'd'
     signed double-cell integer
'ud'
     unsigned double-cell integer
'r'
     Float (on the FP stack)

   You can find a more complete list in *note Notation::.

     Assignment: Write stack-effect comments for all definitions you
     have written up to now.

3.12 Types
==========

In Forth the names of the operations are not overloaded; so similar
operations on different types need different names; e.g., '+' adds
integers, and you have to use 'f+' to add floating-point numbers.  The
following prefixes are often used for related operations on different
types:

'(none)'
     signed integer
'u'
     unsigned integer
'c'
     character
'd'
     signed double-cell integer
'ud, du'
     unsigned double-cell integer
'2'
     two cells (not-necessarily double-cell numbers)
'm, um'
     mixed single-cell and double-cell operations
'f'
     floating-point (note that in stack comments 'f' represents flags,
     and 'r' represents FP numbers; also, you need to include the
     exponent part in literal FP numbers, *note Floating Point
     Tutorial::).

   If there are no differences between the signed and the unsigned
variant (e.g., for '+'), there is only the prefix-less variant.

   Forth does not perform type checking, neither at compile time, nor at
run time.  If you use the wrong operation, the data are interpreted
incorrectly:

     -1 u.

   If you have only experience with type-checked languages until now,
and have heard how important type-checking is, don't panic!  In my
experience (and that of other Forthers), type errors in Forth code are
usually easy to find (once you get used to it), the increased vigilance
of the programmer tends to catch some harder errors in addition to most
type errors, and you never have to work around the type system, so in
most situations the lack of type-checking seems to be a win (projects to
add type checking to Forth have not caught on).

3.13 Factoring
==============

If you try to write longer definitions, you will soon find it hard to
keep track of the stack contents.  Therefore, good Forth programmers
tend to write only short definitions (e.g., three lines).  The art of
finding meaningful short definitions is known as factoring (as in
factoring polynomials).

   Well-factored programs offer additional advantages: smaller, more
general words, are easier to test and debug and can be reused more and
better than larger, specialized words.

   So, if you run into difficulties with stack management, when writing
code, try to define meaningful factors for the word, and define the word
in terms of those.  Even if a factor contains only two words, it is
often helpful.

   Good factoring is not easy, and it takes some practice to get the
knack for it; but even experienced Forth programmers often don't find
the right solution right away, but only when rewriting the program.  So,
if you don't come up with a good solution immediately, keep trying,
don't despair.

3.14 Designing the stack effect
===============================

In other languages you can use an arbitrary order of parameters for a
function; and since there is only one result, you don't have to deal
with the order of results, either.

   In Forth (and other stack-based languages, e.g., PostScript) the
parameter and result order of a definition is important and should be
designed well.  The general guideline is to design the stack effect such
that the word is simple to use in most cases, even if that complicates
the implementation of the word.  Some concrete rules are:

   * Words consume all of their parameters (e.g., '.').

   * If there is a convention on the order of parameters (e.g., from
     mathematics or another programming language), stick with it (e.g.,
     '-').

   * If one parameter usually requires only a short computation (e.g.,
     it is a constant), pass it on the top of the stack.  Conversely,
     parameters that usually require a long sequence of code to compute
     should be passed as the bottom (i.e., first) parameter.  This makes
     the code easier to read, because the reader does not need to keep
     track of the bottom item through a long sequence of code (or,
     alternatively, through stack manipulations).  E.g., '!' (store,
     *note Memory::) expects the address on top of the stack because it
     is usually simpler to compute than the stored value (often the
     address is just a variable).

   * Similarly, results that are usually consumed quickly should be
     returned on the top of stack, whereas a result that is often used
     in long computations should be passed as bottom result.  E.g., the
     file words like 'open-file' return the error code on the top of
     stack, because it is usually consumed quickly by 'throw'; moreover,
     the error code has to be checked before doing anything with the
     other results.

   These rules are just general guidelines, don't lose sight of the
overall goal to make the words easy to use.  E.g., if the convention
rule conflicts with the computation-length rule, you might decide in
favour of the convention if the word will be used rarely, and in favour
of the computation-length rule if the word will be used frequently
(because with frequent use the cost of breaking the computation-length
rule would be quite high, and frequent use makes it easier to remember
an unconventional order).

3.15 Local Variables
====================

You can define local variables (_locals_) in a colon definition:

     : swap { a b -- b a }
       b a ;
     1 2 swap .s 2drop

   (If your Forth system does not support this syntax, include
'compat/anslocal.fs' first).

   In this example '{ a b -- b a }' is the locals definition; it takes
two cells from the stack, puts the top of stack in 'b' and the next
stack element in 'a'.  '--' starts a comment ending with '}'.  After the
locals definition, using the name of the local will push its value on
the stack.  You can omit the comment part ('-- b a'):

     : swap ( x1 x2 -- x2 x1 )
       { a b } b a ;

   In Gforth you can have several locals definitions, anywhere in a
colon definition; in contrast, in a standard program you can have only
one locals definition per colon definition, and that locals definition
must be outside any control structure.

   With locals you can write slightly longer definitions without running
into stack trouble.  However, I recommend trying to write colon
definitions without locals for exercise purposes to help you gain the
essential factoring skills.

     Assignment: Rewrite your definitions until now with locals

   Reference: *note Locals::.

3.16 Conditional execution
==========================

In Forth you can use control structures only inside colon definitions.
An 'if'-structure looks like this:

     : abs ( n1 -- +n2 )
         dup 0 < if
             negate
         endif ;
     5 abs .
     -5 abs .

   'if' takes a flag from the stack.  If the flag is non-zero (true),
the following code is performed, otherwise execution continues after the
'endif' (or 'else').  '<' compares the top two stack elements and
produces a flag:

     1 2 < .
     2 1 < .
     1 1 < .

   Actually the standard name for 'endif' is 'then'.  This tutorial
presents the examples using 'endif', because this is often less
confusing for people familiar with other programming languages where
'then' has a different meaning.  If your system does not have 'endif',
define it with

     : endif postpone then ; immediate

   You can optionally use an 'else'-part:

     : min ( n1 n2 -- n )
       2dup < if
         drop
       else
         nip
       endif ;
     2 3 min .
     3 2 min .

     Assignment: Write 'min' without 'else'-part (hint: what's the
     definition of 'nip'?).

   Reference: *note Selection::.

3.17 Flags and Comparisons
==========================

In a false-flag all bits are clear (0 when interpreted as integer).  In
a canonical true-flag all bits are set (-1 as a twos-complement signed
integer); in many contexts (e.g., 'if') any non-zero value is treated as
true flag.

     false .
     true .
     true hex u. decimal

   Comparison words produce canonical flags:

     1 1 = .
     1 0= .
     0 1 < .
     0 0 < .
     -1 1 u< . \ type error, u< interprets -1 as large unsigned number
     -1 1 < .

   Gforth supports all combinations of the prefixes '0 u d d0 du f f0'
(or none) and the comparisons '= <> < > <= >='.  Only a part of these
combinations are standard (for details see the standard, *note Numeric
comparison::, *note Floating Point:: or *note Word Index::).

   You can use 'and or xor invert' as operations on canonical flags.
Actually they are bitwise operations:

     1 2 and .
     1 2 or .
     1 3 xor .
     1 invert .

   You can convert a zero/non-zero flag into a canonical flag with '0<>'
(and complement it on the way with '0='; indeed, it is more common to
use '0=' instead of 'invert' for canonical flags).

     1 0= .
     1 0<> .

   While you can use 'if' without '0<>' to test for zero/non-zero, you
sometimes need to use '0<>' when combining zero/non-zero values with
'and or xor' because of their bitwise nature.  The simplest, least
error-prone, and probably clearest way is to use '0<>' in all these
cases, but in some cases you can use fewer '0<>'s.  Here are some stack
effects, where fc represents a canonical flag, and fz represents
zero/non-zero (every fc also works as fz):

     or  ( fz1 fz2 -- fz3 )
     and ( fz1 fc  -- fz2 )
     and ( fc  fz1 -- fz2 )

   So, if you see code like this:

     ( n1 n2 ) 0<> and if

   This tests whether n1 and n2 are non-zero and if yes, performs the
code after 'if'; it treats n1 as zero/non-zero and uses '0<>' to convert
n2 into a canonical flag; the 'and' then produces an fz, which is
consumed by the 'if'.

   You can use the all-bits-set feature of canonical flags and the
bitwise operation of the Boolean operations to avoid 'if's:

     : foo ( n1 -- n2 )
       0= if
         14
       else
         0
       endif ;
     0 foo .
     1 foo .

     : foo ( n1 -- n2 )
       0= 14 and ;
     0 foo .
     1 foo .

     Assignment: Write 'min' without 'if'.

   For reference, see *note Boolean Flags::, *note Numeric comparison::,
and *note Bitwise operations::.

3.18 General Loops
==================

The endless loop is the most simple one:

     : endless ( -- )
       0 begin
         dup . 1+
       again ;
     endless

   Terminate this loop by pressing 'Ctrl-C' (in Gforth).  'begin' does
nothing at run-time, 'again' jumps back to 'begin'.

   A loop with one exit at any place looks like this:

     : log2 ( +n1 -- n2 )
     \ logarithmus dualis of n1>0, rounded down to the next integer
       assert( dup 0> )
       2/ 0 begin
         over 0> while
           1+ swap 2/ swap
       repeat
       nip ;
     7 log2 .
     8 log2 .

   At run-time 'while' consumes a flag; if it is 0, execution continues
behind the 'repeat'; if the flag is non-zero, execution continues behind
the 'while'.  'Repeat' jumps back to 'begin', just like 'again'.

   In Forth there are a number of combinations/abbreviations, like '1+'.
However, '2/' is not one of them; it shifts its argument right by one
bit (arithmetic shift right), and viewed as division that always rounds
towards negative infinity (floored division), like Gforth's '/' (since
Gforth 0.7), but unlike '/' in many other Forth systems.

     -5 2 / . \ -2 or -3
     -5 2/ .  \ -3

   'assert(' is no standard word, but you can get it on systems other
than Gforth by including 'compat/assert.fs'.  You can see what it does
by trying

     0 log2 .

   Here's a loop with an exit at the end:

     : log2 ( +n1 -- n2 )
     \ logarithmus dualis of n1>0, rounded down to the next integer
       assert( dup 0 > )
       -1 begin
         1+ swap 2/ swap
         over 0 <=
       until
       nip ;

   'Until' consumes a flag; if it is zero, execution continues at the
'begin', otherwise after the 'until'.

     Assignment: Write a definition for computing the greatest common
     divisor.

   Reference: *note Simple Loops::.

3.19 Counted loops
==================

     : ^ ( n1 u -- n )
     \ n = the uth power of n1
       1 swap 0 u+do
         over *
       loop
       nip ;
     3 2 ^ .
     4 3 ^ .

   'U+do' (from 'compat/loops.fs', if your Forth system doesn't have it)
takes two numbers of the stack '( u3 u4 -- )', and then performs the
code between 'u+do' and 'loop' for 'u3-u4' times (or not at all, if
'u3-u4<0').

   You can see the stack effect design rules at work in the stack effect
of the loop start words: Since the start value of the loop is more
frequently constant than the end value, the start value is passed on the
top-of-stack.

   You can access the counter of a counted loop with 'i':

     : fac ( u -- u! )
       1 swap 1+ 1 u+do
         i *
       loop ;
     5 fac .
     7 fac .

   There is also '+do', which expects signed numbers (important for
deciding whether to enter the loop).

     Assignment: Write a definition for computing the nth Fibonacci
     number.

   You can also use increments other than 1:

     : up2 ( n1 n2 -- )
       +do
         i .
       2 +loop ;
     10 0 up2

     : down2 ( n1 n2 -- )
       -do
         i .
       2 -loop ;
     0 10 down2

   Reference: *note Counted Loops::.

3.20 Recursion
==============

Usually the name of a definition is not visible in the definition; but
earlier definitions are usually visible:

     1 0 / . \ "Floating-point unidentified fault" in Gforth on some platforms
     : / ( n1 n2 -- n )
       dup 0= if
         -10 throw \ report division by zero
       endif
       /           \ old version
     ;
     1 0 /

   For recursive definitions you can use 'recursive' (non-standard) or
'recurse':

     : fac1 ( n -- n! ) recursive
      dup 0> if
        dup 1- fac1 *
      else
        drop 1
      endif ;
     7 fac1 .

     : fac2 ( n -- n! )
      dup 0> if
        dup 1- recurse *
      else
        drop 1
      endif ;
     8 fac2 .

     Assignment: Write a recursive definition for computing the nth
     Fibonacci number.

   Reference (including indirect recursion): *Note Calls and returns::.

3.21 Leaving definitions or loops
=================================

'EXIT' exits the current definition right away.  For every counted loop
that is left in this way, an 'UNLOOP' has to be performed before the
'EXIT':

     : ...
      ... u+do
        ... if
          ... unloop exit
        endif
        ...
      loop
      ... ;

   'LEAVE' leaves the innermost counted loop right away:

     : ...
      ... u+do
        ... if
          ... leave
        endif
        ...
      loop
      ... ;

   Reference: *note Calls and returns::, *note Counted Loops::.

3.22 Return Stack
=================

In addition to the data stack Forth also has a second stack, the return
stack; most Forth systems store the return addresses of procedure calls
there (thus its name).  Programmers can also use this stack:

     : foo ( n1 n2 -- )
      .s
      >r .s
      r@ .
      >r .s
      r@ .
      r> .
      r@ .
      r> . ;
     1 2 foo

   '>r' takes an element from the data stack and pushes it onto the
return stack; conversely, 'r>' moves an element from the return to the
data stack; 'r@' pushes a copy of the top of the return stack on the
data stack.

   Forth programmers usually use the return stack for storing data
temporarily, if using the data stack alone would be too complex, and
factoring and locals are not an option:

     : 2swap ( x1 x2 x3 x4 -- x3 x4 x1 x2 )
      rot >r rot r> ;

   The return address of the definition and the loop control parameters
of counted loops usually reside on the return stack, so you have to take
all items, that you have pushed on the return stack in a colon
definition or counted loop, from the return stack before the definition
or loop ends.  You cannot access items that you pushed on the return
stack outside some definition or loop within the definition of loop.

   If you miscount the return stack items, this usually ends in a crash:

     : crash ( n -- )
       >r ;
     5 crash

   You cannot mix using locals and using the return stack (according to
the standard; Gforth has no problem).  However, they solve the same
problems, so this shouldn't be an issue.

     Assignment: Can you rewrite any of the definitions you wrote until
     now in a better way using the return stack?

   Reference: *note Return stack::.

3.23 Memory
===========

You can create a global variable 'v' with

     variable v ( -- addr )

   'v' pushes the address of a cell in memory on the stack.  This cell
was reserved by 'variable'.  You can use '!' (store) to store values
from the stack into this cell and '@' (fetch) to load the value from
memory onto the stack:

     v .
     5 v ! .s
     v @ .

   You can see a raw dump of memory with 'dump':

     v 1 cells .s dump

   'Cells ( n1 -- n2 )' gives you the number of bytes (or, more
generally, address units (aus)) that 'n1 cells' occupy.  You can also
reserve more memory:

     create v2 20 cells allot
     v2 20 cells dump

   creates a variable-like word 'v2' and reserves 20 uninitialized
cells; the address pushed by 'v2' points to the start of these 20 cells
(*note CREATE::).  You can use address arithmetic to access these cells:

     3 v2 5 cells + !
     v2 20 cells dump

   You can reserve and initialize memory with ',':

     create v3
       5 , 4 , 3 , 2 , 1 ,
     v3 @ .
     v3 cell+ @ .
     v3 2 cells + @ .
     v3 5 cells dump

     Assignment: Write a definition 'vsum ( addr u -- n )' that computes
     the sum of 'u' cells, with the first of these cells at 'addr', the
     next one at 'addr cell+' etc.

   The difference between 'variable' and 'create' is that 'variable'
allots a cell, and that you cannot allot additional memory to a variable
in standard Forth.

   You can also reserve memory without creating a new word:

     here 10 cells allot .
     here .

   The first 'here' pushes the start address of the memory area, the
second 'here' the address after the dictionary area.  You should store
the start address somewhere, or you will have a hard time finding the
memory area again.

   'Allot' manages dictionary memory.  The dictionary memory contains
the system's data structures for words etc.  on Gforth and most other
Forth systems.  It is managed like a stack: You can free the memory that
you have just 'allot'ed with

     -10 cells allot
     here .

   Note that you cannot do this if you have created a new word in the
meantime (because then your 'allot'ed memory is no longer on the top of
the dictionary "stack").

   Alternatively, you can use 'allocate' and 'free' which allow freeing
memory in any order:

     10 cells allocate throw .s
     20 cells allocate throw .s
     swap
     free throw
     free throw

   The 'throw's deal with errors (e.g., out of memory).

   And there is also a garbage collector
(https://www.complang.tuwien.ac.at/forth/garbage-collection.zip), which
eliminates the need to 'free' memory explicitly.

   Reference: *note Memory::.

3.24 Characters and Strings
===========================

On the stack characters take up a cell, like numbers.  In memory they
have their own size (one 8-bit byte on most systems), and therefore
require their own words for memory access:

     create v4
       104 c, 97 c, 108 c, 108 c, 111 c,
     v4 4 chars + c@ .
     v4 5 chars dump

   The preferred representation of strings on the stack is 'addr
u-count', where 'addr' is the address of the first character and
'u-count' is the number of characters in the string.

     v4 5 type

   You get a string constant with

     s" hello, world" .s
     type

   Make sure you have a space between 's"' and the string; 's"' is a
normal Forth word and must be delimited with white space (try what
happens when you remove the space).

   However, this interpretive use of 's"' is quite restricted: the
string exists only until the next call of 's"' (some Forth systems keep
more than one of these strings, but usually they still have a limited
lifetime).

     s" hello," s" world" .s
     type
     type

   You can also use 's"' in a definition, and the resulting strings then
live forever (well, for as long as the definition):

     : foo s" hello," s" world" ;
     foo .s
     type
     type

     Assignment: 'Emit ( c -- )' types 'c' as character (not a number).
     Implement 'type ( addr u -- )'.

   Reference: *note Memory Blocks::.

3.25 Alignment
==============

On many processors cells have to be aligned in memory, if you want to
access them with '@' and '!' (and even if the processor does not require
alignment, access to aligned cells is faster).

   'Create' aligns 'here' (i.e., the place where the next allocation
will occur, and that the 'create'd word points to).  Likewise, the
memory produced by 'allocate' starts at an aligned address.  Adding a
number of 'cells' to an aligned address produces another aligned
address.

   However, address arithmetic involving 'char+' and 'chars' can create
an address that is not cell-aligned.  'Aligned ( addr -- a-addr )'
produces the next aligned address:

     v3 char+ aligned .s @ .
     v3 char+ .s @ .

   Similarly, 'align' advances 'here' to the next aligned address:

     create v5 97 c,
     here .
     align here .
     1000 ,

   Note that you should use aligned addresses even if your processor
does not require them, if you want your program to be portable.

   Reference: *note Address arithmetic::.

3.26 Floating Point
===================

Floating-point (FP) numbers and arithmetic in Forth works mostly as one
might expect, but there are a few things worth noting:

   The first point is not specific to Forth, but so important and yet
not universally known that I mention it here: FP numbers are not reals.
Many properties (e.g., arithmetic laws) that reals have and that one
expects of all kinds of numbers do not hold for FP numbers.  If you want
to use FP computations, you should learn about their problems and how to
avoid them; a good starting point is 'David Goldberg, What Every
Computer Scientist Should Know About Floating-Point Arithmetic
(https://docs.oracle.com/cd/E19957-01/806-3568/ncg_goldberg.html), ACM
Computing Surveys 23(1):5-48, March 1991'.

   In Forth source code literal FP numbers need an exponent, e.g.,
'1e0'; this can also be written shorter as '1e', longer as '+1.0e+0',
and many variations in between.  The reason for this is that, for
historical reasons, Forth interprets a decimal point alone (e.g., '1.')
as indicating a double-cell integer.  Examples:

     2e 2e f+ f.

   Another requirement for literal FP numbers is that the current base
is decimal; with a hex base '1e' is interpreted as an integer.

   Forth has a separate stack for FP numbers in conformance with
Forth-2012.  One advantage of this model is that cells are not in the
way when accessing FP values, and vice versa.  Forth has a set of words
for manipulating the FP stack: 'fdup fswap fdrop fover frot' and
(non-standard) 'fnip ftuck fpick'.

   FP arithmetic words are prefixed with 'F'.  There is the usual set
'f+ f- f* f/ f** fnegate' as well as a number of words for other
functions, e.g., 'fsqrt fsin fln fmin'.  One word that you might expect
is 'f='; but 'f=' is non-standard, because FP computation results are
usually inaccurate, so exact comparison is usually a mistake, and one
should use approximate comparison.  Unfortunately, 'f~', the standard
word for that purpose, is not well designed, so Gforth provides 'f~abs'
and 'f~rel' as well.

   And of course there are words for accessing FP numbers in memory ('f@
f!'), and for address arithmetic ('floats float+ faligned').  There are
also variants of these words with an 'sf' and 'df' prefix for accessing
IEEE format single-precision and double-precision numbers in memory;
their main purpose is for accessing external FP data (e.g., that has
been read from or will be written to a file).

   Here is an example of a dot-product word and its use:

     : v* ( f_addr1 nstride1 f_addr2 nstride2 ucount -- r )
       >r swap 2swap swap 0e r> 0 ?DO
         dup f@ over + 2swap dup f@ f* f+ over + 2swap
       LOOP
       2drop 2drop ;

     create v 1.23e f, 4.56e f, 7.89e f,

     v 1 floats  v 1 floats  3  v* f.

     Assignment: Write a program to solve a quadratic equation.  Then
     read 'Henry G. Baker, You Could Learn a Lot from a Quadratic
     (https://citeseerx.ist.psu.edu/viewdoc/download?doi=10.1.1.111.4448&rep=rep1&type=pdf),
     ACM SIGPLAN Notices, 33(1):30-39, January 1998', and see if you can
     improve your program.  Finally, find a test case where the original
     and the improved version produce different results.

   Reference: *note Floating Point::; *note Floating point stack::;
*note Number Conversion::; *note Memory Access::; *note Address
arithmetic::.

3.27 Files
==========

This section gives a short introduction into how to use files inside
Forth.  It's broken up into five easy steps:

  1. Open an ASCII text file for input
  2. Open a file for output
  3. Read input file until string matches (or some other condition is
     met)
  4. Write some lines from input (modified or not) to output
  5. Close the files.

   Reference: *note General files::.

3.27.1 Open file for input
--------------------------

     s" foo.in"  r/o open-file throw Value fd-in

3.27.2 Create file for output
-----------------------------

     s" foo.out" w/o create-file throw Value fd-out

   The available file modes are r/o for read-only access, r/w for
read-write access, and w/o for write-only access.  You could open both
files with r/w, too, if you like.  All file words return error codes;
for most applications, it's best to pass there error codes with 'throw'
to the outer error handler.

   If you want words for opening and assigning, define them as follows:

     0 Value fd-in
     0 Value fd-out
     : open-input ( addr u -- )  r/o open-file throw to fd-in ;
     : open-output ( addr u -- )  w/o create-file throw to fd-out ;

   Usage example:

     s" foo.in" open-input
     s" foo.out" open-output

3.27.3 Scan file for a particular line
--------------------------------------

     256 Constant max-line
     Create line-buffer  max-line 2 + allot

     : scan-file ( addr u -- )
       begin
           line-buffer max-line fd-in read-line throw
       while
              >r 2dup line-buffer r> compare 0=
          until
       else
          drop
       then
       2drop ;

   'read-line ( addr u1 fd -- u2 flag ior )' reads up to u1 bytes into
the buffer at addr, and returns the number of bytes read, a flag that is
false when the end of file is reached, and an error code.

   'compare ( addr1 u1 addr2 u2 -- n )' compares two strings and returns
zero if both strings are equal.  It returns a positive number if the
first string is lexically greater, a negative if the second string is
lexically greater.

   We haven't seen this loop here; it has two exits.  Since the 'while'
exits with the number of bytes read on the stack, we have to clean up
that separately; that's after the 'else'.

   Usage example:

     s" The text I search is here" scan-file

3.27.4 Copy input to output
---------------------------

     : copy-file ( -- )
       begin
           line-buffer max-line fd-in read-line throw
       while
           line-buffer swap fd-out write-line throw
       repeat
       drop ;

3.27.5 Close files
------------------

     fd-in close-file throw
     fd-out close-file throw

   Likewise, you can put that into definitions, too:

     : close-input ( -- )  fd-in close-file throw ;
     : close-output ( -- )  fd-out close-file throw ;

     Assignment: How could you modify 'copy-file' so that it copies
     until a second line is matched?  Can you write a program that
     extracts a section of a text file, given the line that starts and
     the line that terminates that section?

3.28 Interpretation and Compilation Semantics and Immediacy
===========================================================

When a word is compiled, it behaves differently from being interpreted.
E.g., consider '+':

     1 2 + .
     : foo + ;

   These two behaviours are known as compilation and interpretation
semantics.  For normal words (e.g., '+'), the compilation semantics is
to append the interpretation semantics to the currently defined word
('foo' in the example above).  I.e., when 'foo' is executed later, the
interpretation semantics of '+' (i.e., adding two numbers) will be
performed.

   However, there are words with non-default compilation semantics,
e.g., the control-flow words like 'if'.  You can use 'immediate' to
change the compilation semantics of the last defined word to be equal to
the interpretation semantics:

     : [FOO] ( -- )
      5 . ; immediate

     [FOO]
     : bar ( -- )
       [FOO] ;
     bar
     see bar

   Two conventions to mark words with non-default compilation semantics
are names with brackets (more frequently used) and to write them all in
upper case (less frequently used).

   For some words, such as 'if', using their interpretation semantics is
usually a mistake, so we mark them as 'compile-only', and you get a
warning when you interpret them.

     : flip ( -- )
      6 . ; compile-only \ but not immediate
     flip

     : flop ( -- )
      flip ;
     flop

   In this example, first the interpretation semantics of 'flip' is used
(and you get a warning); the second use of 'flip' uses the compilation
semantics (and you get no warning).  You can also see in this example
that compile-only is a property that is evaluated at text interpretation
time, not at run-time.

   The text interpreter has two states: in interpret state, it performs
the interpretation semantics of words it encounters; in compile state,
it performs the compilation semantics of these words.

   Among other things, ':' switches into compile state, and ';' switches
back to interpret state.  They contain the factors ']' (switch to
compile state) and '[' (switch to interpret state), that do nothing but
switch the state.

     : xxx ( -- )
       [ 5 . ]
     ;

     xxx
     see xxx

   These brackets are also the source of the naming convention mentioned
above.

   Reference: *note Interpretation and Compilation Semantics::.

3.29 Execution Tokens
=====================

'' word' gives you the execution token (XT) of a word.  The XT is a cell
representing the interpretation semantics of a word.  You can execute
this semantics with 'execute':

     ' + .s
     1 2 rot execute .

   The XT is similar to a function pointer in C. However, parameter
passing through the stack makes it a little more flexible:

     : map-array ( ... addr u xt -- ... )
     \ executes xt ( ... x -- ... ) for every element of the array starting
     \ at addr and containing u elements
       { xt }
       cells over + swap ?do
         i @ xt execute
       1 cells +loop ;

     create a 3 , 4 , 2 , -1 , 4 ,
     a 5 ' . map-array .s
     0 a 5 ' + map-array .
     s" max-n" environment? drop .s
     a 5 ' min map-array .

   You can use map-array with the XTs of words that consume one element
more than they produce.  In theory you can also use it with other XTs,
but the stack effect then depends on the size of the array, which is
hard to understand.

   Since XTs are cell-sized, you can store them in memory and manipulate
them on the stack like other cells.  You can also compile the XT into a
word with 'compile,':

     : foo1 ( n1 n2 -- n )
        [ ' + compile, ] ;
     see foo1

   This is non-standard, because 'compile,' has no compilation semantics
in the standard, but it works in good Forth systems.  For the broken
ones, use

     : [compile,] compile, ; immediate

     : foo1 ( n1 n2 -- n )
        [ ' + ] [compile,] ;
     see foo1

   ''' is a word with default compilation semantics; it parses the next
word when its interpretation semantics are executed, not during
compilation:

     : foo ( -- xt )
       ' ;
     see foo
     : bar ( ... "word" -- ... )
       ' execute ;
     see bar
     1 2 bar + .

   You often want to parse a word during compilation and compile its XT
so it will be pushed on the stack at run-time.  '[']' does this:

     : xt-+ ( -- xt )
       ['] + ;
     see xt-+
     1 2 xt-+ execute .

   Many programmers tend to see ''' and the word it parses as one unit,
and expect it to behave like '[']' when compiled, and are confused by
the actual behaviour.  If you are, just remember that the Forth system
just takes ''' as one unit and has no idea that it is a parsing word
(attempts to convenience programmers in this issue have usually resulted
in even worse pitfalls, see 'State'-smartness---Why it is evil and How to
Exorcise it (https://www.complang.tuwien.ac.at/papers/ertl98.ps.gz)).

   Note that the state of the interpreter does not come into play when
creating and executing XTs.  I.e., even when you execute ''' in compile
state, it still gives you the interpretation semantics.  And whatever
that state is, 'execute' performs the semantics represented by the XT
(i.e., for XTs produced with ''' the interpretation semantics).

   Reference: *note Tokens for Words::.

3.30 Exceptions
===============

'throw ( n -- )' causes an exception unless n is zero.

     100 throw .s
     0 throw .s

   'catch ( ... xt -- ... n )' behaves similar to 'execute', but it
catches exceptions and pushes the number of the exception on the stack
(or 0, if the xt executed without exception).  If there was an
exception, the stacks have the same depth as when entering 'catch':

     .s
     3 0 ' / catch .s
     3 2 ' / catch .s

     Assignment: Try the same with 'execute' instead of 'catch'.

   'Throw' always jumps to the dynamically next enclosing 'catch', even
if it has to leave several call levels to achieve this:

     : foo 100 throw ;
     : foo1 foo ." after foo" ;
     : bar ['] foo1 catch ;
     bar .

   It is often important to restore a value upon leaving a definition,
even if the definition is left through an exception.  You can ensure
this like this:

     : ...
        save-x
        ['] word-changing-x catch ( ... n )
        restore-x
        ( ... n ) throw ;

   However, this is still not safe against, e.g., the user pressing
'Ctrl-C' when execution is between the 'catch' and 'restore-x'.

   Gforth provides an alternative exception handling syntax that is safe
against such cases: 'try ... restore ... endtry'.  If the code between
'try' and 'endtry' has an exception, the stack depths are restored, the
exception number is pushed on the stack, and the execution continues
right after 'restore'.

   The safer equivalent to the restoration code above is

     : ...
       save-x
       try
         word-changing-x 0
       restore
         restore-x
       endtry
       throw ;

   Reference: *note Exception Handling::.

3.31 Defining Words
===================

':', 'create', and 'variable' are definition words: They define other
words.  'Constant' is another definition word:

     5 constant foo
     foo .

   You can also use the prefixes '2' (double-cell) and 'f' (floating
point) with 'variable' and 'constant'.

   You can also define your own defining words.  E.g.:

     : variable ( "name" -- )
       create 0 , ;

   You can also define defining words that create words that do
something other than just producing their address:

     : constant ( n "name" -- )
       create ,
     does> ( -- n )
       ( addr ) @ ;

     5 constant foo
     foo .

   The definition of 'constant' above ends at the 'does>'; i.e., 'does>'
replaces ';', but it also does something else: It changes the last
defined word such that it pushes the address of the body of the word and
then performs the code after the 'does>' whenever it is called.

   In the example above, 'constant' uses ',' to store 5 into the body of
'foo'.  When 'foo' executes, it pushes the address of the body onto the
stack, then (in the code after the 'does>') fetches the 5 from there.

   The stack comment near the 'does>' reflects the stack effect of the
defined word, not the stack effect of the code after the 'does>' (the
difference is that the code expects the address of the body that the
stack comment does not show).

   You can use these definition words to do factoring in cases that
involve (other) definition words.  E.g., a field offset is always added
to an address.  Instead of defining

     2 cells constant offset-field1

   and using this like

     ( addr ) offset-field1 +

   you can define a definition word

     : simple-field ( n "name" -- )
       create ,
     does> ( n1 -- n1+n )
       ( addr ) @ + ;

   Definition and use of field offsets now look like this:

     2 cells simple-field field1
     create mystruct 4 cells allot
     mystruct .s field1 .s drop

   If you want to do something with the word without performing the code
after the 'does>', you can access the body of a 'create'd word with
'>body ( xt -- addr )':

     : value ( n "name" -- )
       create ,
     does> ( -- n1 )
       @ ;
     : to ( n "name" -- )
       ' >body ! ;

     5 value foo
     foo .
     7 to foo
     foo .

     Assignment: Define 'defer ( "name" -- )', which creates a word that
     stores an XT (at the start the XT of 'abort'), and upon execution
     'execute's the XT. Define 'is ( xt "name" -- )' that stores 'xt'
     into 'name', a word defined with 'defer'.  Indirect recursion is
     one application of 'defer'.

   Reference: *note User-defined Defining Words::.

3.32 Arrays and Records
=======================

Forth has no standard words for defining arrays, but you can build them
yourself based on address arithmetic.  You can also define words for
defining arrays and records (*note Defining Words: Defining Words
Tutorial.).

   One of the first projects a Forth newcomer sets out upon when
learning about defining words is an array defining word (possibly for
n-dimensional arrays).  Go ahead and do it, I did it, too; you will
learn something from it.  However, don't be disappointed when you later
learn that you have little use for these words (inappropriate use would
be even worse).  I have not found a set of useful array words yet; the
needs are just too diverse, and named, global arrays (the result of
naive use of defining words) are often not flexible enough (e.g.,
consider how to pass them as parameters).  Another such project is a set
of words to help dealing with strings.

   On the other hand, there is a useful set of record words, and it has
been defined in 'compat/struct.fs'; these words are predefined in
Gforth.  They are explained in depth elsewhere in this manual (see *note
Structures::).  The 'simple-field' example above is simplified variant
of fields in this package.

3.33 'POSTPONE'
===============

You can compile the compilation semantics (instead of compiling the
interpretation semantics) of a word with 'POSTPONE':

     : MY-+ ( Compilation: -- ; Run-time of compiled code: n1 n2 -- n )
      POSTPONE + ; immediate
     : foo ( n1 n2 -- n )
      MY-+ ;
     1 2 foo .
     see foo

   During the definition of 'foo' the text interpreter performs the
compilation semantics of 'MY-+', which performs the compilation
semantics of '+', i.e., it compiles '+' into 'foo'.

   This example also displays separate stack comments for the
compilation semantics and for the stack effect of the compiled code.
For words with default compilation semantics these stack effects are
usually not displayed; the stack effect of the compilation semantics is
always '( -- )' for these words, the stack effect for the compiled code
is the stack effect of the interpretation semantics.

   Note that the state of the interpreter does not come into play when
performing the compilation semantics in this way.  You can also perform
it interpretively, e.g.:

     : foo2 ( n1 n2 -- n )
      [ MY-+ ] ;
     1 2 foo .
     see foo

   However, there are some broken Forth systems where this does not
always work, and therefore this practice was been declared non-standard
in 1999.

   Here is another example for using 'POSTPONE':

     : MY-- ( Compilation: -- ; Run-time of compiled code: n1 n2 -- n )
      POSTPONE negate POSTPONE + ; immediate compile-only
     : bar ( n1 n2 -- n )
       MY-- ;
     2 1 bar .
     see bar

   You can define 'ENDIF' in this way:

     : ENDIF ( Compilation: orig -- )
       POSTPONE then ; immediate

     Assignment: Write 'MY-2DUP' that has compilation semantics
     equivalent to '2dup', but compiles 'over over'.

3.34 'Literal'
==============

You cannot 'POSTPONE' numbers:

     : [FOO] POSTPONE 500 ; immediate

   Instead, you can use 'LITERAL (compilation: n --; run-time: -- n )':

     : [FOO] ( compilation: --; run-time: -- n )
       500 POSTPONE literal ; immediate

     : flip [FOO] ;
     flip .
     see flip

   'LITERAL' consumes a number at compile-time (when it's compilation
semantics are executed) and pushes it at run-time (when the code it
compiled is executed).  A frequent use of 'LITERAL' is to compile a
number computed at compile time into the current word:

     : bar ( -- n )
       [ 2 2 + ] literal ;
     see bar

     Assignment: Write ']L' which allows writing the example above as ':
     bar ( -- n ) [ 2 2 + ]L ;'

3.35 Advanced macros
====================

Reconsider 'map-array' from *note Execution Tokens: Execution Tokens
Tutorial.  It frequently performs 'execute', a relatively expensive
operation in some Forth implementations.  You can use 'compile,' and
'POSTPONE' to eliminate these 'execute's and produce a word that
contains the word to be performed directly:

     : compile-map-array ( compilation: xt -- ; run-time: ... addr u -- ... )
     \ at run-time, execute xt ( ... x -- ... ) for each element of the
     \ array beginning at addr and containing u elements
       { xt }
       POSTPONE cells POSTPONE over POSTPONE + POSTPONE swap POSTPONE ?do
         POSTPONE i POSTPONE @ xt compile,
       1 cells POSTPONE literal POSTPONE +loop ;

     : sum-array ( addr u -- n )
      0 rot rot [ ' + compile-map-array ] ;
     see sum-array
     a 5 sum-array .

   You can use the full power of Forth for generating the code; here's
an example where the code is generated in a loop:

     : compile-vmul-step ( compilation: n --; run-time: n1 addr1 -- n2 addr2 )
     \ n2=n1+(addr1)*n, addr2=addr1+cell
       POSTPONE tuck POSTPONE @
       POSTPONE literal POSTPONE * POSTPONE +
       POSTPONE swap POSTPONE cell+ ;

     : compile-vmul ( compilation: addr1 u -- ; run-time: addr2 -- n )
     \ n=v1*v2 (inner product), where the v_i are represented as addr_i u
       0 postpone literal postpone swap
       [ ' compile-vmul-step compile-map-array ]
       postpone drop ;
     see compile-vmul

     : a-vmul ( addr -- n )
     \ n=a*v, where v is a vector that's as long as a and starts at addr
      [ a 5 compile-vmul ] ;
     see a-vmul
     a a-vmul .

   This example uses 'compile-map-array' to show off, but you could also
use 'map-array' instead (try it now!).

   You can use this technique for efficient multiplication of large
matrices.  In matrix multiplication, you multiply every row of one
matrix with every column of the other matrix.  You can generate the code
for one row once, and use it for every column.  The only downside of
this technique is that it is cumbersome to recover the memory consumed
by the generated code when you are done (and in more complicated cases
it is not possible portably).

3.36 Compilation Tokens
=======================

This section is Gforth-specific.  You can skip it.

   '' word compile,' compiles the interpretation semantics.  For words
with default compilation semantics this is the same as performing the
compilation semantics.  To represent the compilation semantics of other
words (e.g., words like 'if' that have no interpretation semantics),
Gforth has the concept of a compilation token (CT, consisting of two
cells), and words 'comp'' and '[comp']'.  You can perform the
compilation semantics represented by a CT with 'execute':

     : foo2 ( n1 n2 -- n )
        [ comp' + execute ] ;
     see foo

   You can compile the compilation semantics represented by a CT with
'postpone,':

     : foo3 ( -- )
       [ comp' + postpone, ] ;
     see foo3

   '[ comp' word postpone, ]' is equivalent to 'POSTPONE word'.  'comp''
is particularly useful for words that have no interpretation semantics:

     ' if
     comp' if .s 2drop

   Reference: *note Tokens for Words::.

3.37 Wordlists and Search Order
===============================

The dictionary is not just a memory area that allows you to allocate
memory with 'allot', it also contains the Forth words, arranged in
several wordlists.  When searching for a word in a wordlist,
conceptually you start searching at the youngest and proceed towards
older words (in reality most systems nowadays use hash-tables); i.e., if
you define a word with the same name as an older word, the new word
shadows the older word.

   Which wordlists are searched in which order is determined by the
search order.  You can display the search order with 'order'.  It
displays first the search order, starting with the wordlist searched
first, then it displays the wordlist that will contain newly defined
words.

   You can create a new, empty wordlist with 'wordlist ( -- wid )':

     wordlist constant mywords

   'Set-current ( wid -- )' sets the wordlist that will contain newly
defined words (the _current_ wordlist):

     mywords set-current
     order

   Gforth does not display a name for the wordlist in 'mywords' because
this wordlist was created anonymously with 'wordlist'.

   You can get the current wordlist with 'get-current ( -- wid)'.  If
you want to put something into a specific wordlist without overall
effect on the current wordlist, this typically looks like this:

     get-current mywords set-current ( wid )
     create someword
     ( wid ) set-current

   You can write the search order with 'set-order ( wid1 .. widn n -- )'
and read it with 'get-order ( -- wid1 .. widn n )'.  The first searched
wordlist is topmost.

     get-order mywords swap 1+ set-order
     order

   Yes, the order of wordlists in the output of 'order' is reversed from
stack comments and the output of '.s' and thus unintuitive.

     Assignment: Define '>order ( wid -- )' which adds 'wid' as first
     searched wordlist to the search order.  Define 'previous ( -- )',
     which removes the first searched wordlist from the search order.
     Experiment with boundary conditions (you will see some crashes or
     situations that are hard or impossible to leave).

   The search order is a powerful foundation for providing features
similar to Modula-2 modules and C++ namespaces.  However, trying to
modularize programs in this way has disadvantages for debugging and
reuse/factoring that overcome the advantages in my experience (I don't
do huge projects, though).  These disadvantages are not so clear in
other languages/programming environments, because these languages are
not so strong in debugging and reuse.

   Reference: *note Word Lists::.

4 An Introduction to Standard Forth
***********************************

The difference of this chapter from the Tutorial (*note Tutorial::) is
that it is slower-paced in its examples, but uses them to dive deep into
explaining Forth internals (not covered by the Tutorial).  Apart from
that, this chapter covers far less material.  It is suitable for reading
without using a computer.

   The primary purpose of this manual is to document Gforth.  However,
since Forth is not a widely-known language and there is a lack of
up-to-date teaching material, it seems worthwhile to provide some
introductory material.  For other sources of Forth-related information,
see *note Forth-related information::.

   The examples in this section should work on any Standard Forth; the
output shown was produced using Gforth.  Each example attempts to
reproduce the exact output that Gforth produces.  If you try out the
examples (and you should), what you should type is shown 'like this' and
Gforth's response is shown 'like this'.  The single exception is that,
where the example shows <RET> it means that you should press the
"carriage return" key.  Unfortunately, some output formats for this
manual cannot show the difference between 'this' and 'this' which will
make trying out the examples harder (but not impossible).

   Forth is an unusual language.  It provides an interactive development
environment which includes both an interpreter and compiler.  Forth
programming style encourages you to break a problem down into many small
fragments ("factoring"), and then to develop and test each fragment
interactively.  Forth advocates assert that breaking the
edit-compile-test cycle used by conventional programming languages can
lead to great productivity improvements.

4.1 Introducing the Text Interpreter
====================================

When you invoke the Forth image, you will see a startup banner printed
and nothing else (if you have Gforth installed on your system, try
invoking it now, by typing 'gforth<RET>').  Forth is now running its
command line interpreter, which is called the "Text Interpreter" (also
known as the "Outer Interpreter").  (You will learn a lot about the text
interpreter as you read through this chapter, for more detail *note The
Text Interpreter::).

   Although it's not obvious, Forth is actually waiting for your input.
Type a number and press the <RET> key:

     45<RET>  ok

   Rather than give you a prompt to invite you to input something, the
text interpreter prints a status message after it has processed a line
of input.  The status message in this case ("' ok'" followed by
carriage-return) indicates that the text interpreter was able to process
all of your input successfully.  Now type something illegal:

     qwer341<RET>
     *the terminal*:2: Undefined word
     >>>qwer341<<<
     Backtrace:
     $2A95B42A20 throw
     $2A95B57FB8 no.extensions

   The exact text, other than the "Undefined word" may differ slightly
on your system, but the effect is the same; when the text interpreter
detects an error, it discards any remaining text on a line, resets
certain internal state and prints an error message.  For a detailed
description of error messages see *note Error messages::.

   The text interpreter waits for you to press carriage-return, and then
processes your input line.  Starting at the beginning of the line, it
breaks the line into groups of characters separated by spaces.  For each
group of characters in turn, it makes two attempts to do something:

   * It tries to treat it as a command.  It does this by searching a
     "name dictionary".  If the group of characters matches an entry in
     the name dictionary, the name dictionary provides the text
     interpreter with information that allows the text interpreter to
     perform some actions.  In Forth jargon, we say that the group of
     characters names a "word", that the dictionary search returns an
     "execution token (xt)" corresponding to the "definition" of the
     word, and that the text interpreter executes the xt.  Often, the
     terms "word" and "definition" are used interchangeably.
   * If the text interpreter fails to find a match in the name
     dictionary, it tries to treat the group of characters as a number
     in the current number base (when you start up Forth, the current
     number base is base 10).  If the group of characters legitimately
     represents a number, the text interpreter pushes the number onto a
     stack (we'll learn more about that in the next section).

   If the text interpreter is unable to do either of these things with
any group of characters, it discards the group of characters and the
rest of the line, then prints an error message.  If the text interpreter
reaches the end of the line without error, it prints the status message
"' ok'" followed by carriage-return.

   This is the simplest command we can give to the text interpreter:

     <RET>  ok

   The text interpreter did everything we asked it to do (nothing)
without an error, so it said that everything is "' ok'".  Try a slightly
longer command:

     12 dup fred dup<RET>
     *the terminal*:3: Undefined word
     12 dup >>>fred<<< dup
     Backtrace:
     $2A95B42A20 throw
     $2A95B57FB8 no.extensions

   When you press the carriage-return key, the text interpreter starts
to work its way along the line:

   * When it gets to the space after the '2', it takes the group of
     characters '12' and looks them up in the name dictionary(1).  There
     is no match for this group of characters in the name dictionary, so
     it tries to treat them as a number.  It is able to do this
     successfully, so it puts the number, 12, "on the stack" (whatever
     that means).
   * The text interpreter resumes scanning the line and gets the next
     group of characters, 'dup'.  It looks it up in the name dictionary
     and (you'll have to take my word for this) finds it, and executes
     the word 'dup' (whatever that means).
   * Once again, the text interpreter resumes scanning the line and gets
     the group of characters 'fred'.  It looks them up in the name
     dictionary, but can't find them.  It tries to treat them as a
     number, but they don't represent any legal number.

   At this point, the text interpreter gives up and prints an error
message.  The error message shows exactly how far the text interpreter
got in processing the line.  In particular, it shows that the text
interpreter made no attempt to do anything with the final character
group, 'dup', even though we have good reason to believe that the text
interpreter would have no problem looking that word up and executing it
a second time.

   ---------- Footnotes ----------

   (1) We can't tell if it found them or not, but assume for now that it
did not

4.2 Stacks, postfix notation and parameter passing
==================================================

In procedural programming languages (like C and Pascal), the
building-block of programs is the "function" or "procedure".  These
functions or procedures are called with "explicit parameters".  For
example, in C we might write:

     total = total + new_volume(length,height,depth);

where new_volume is a function-call to another piece of code, and total,
length, height and depth are all variables.  length, height and depth
are parameters to the function-call.

   In Forth, the equivalent of the function or procedure is the
"definition" and parameters are implicitly passed between definitions
using a shared stack that is visible to the programmer.  Although Forth
does support variables, the existence of the stack means that they are
used far less often than in most other programming languages.  When the
text interpreter encounters a number, it will place ("push") it on the
stack.  There are several stacks (the actual number is
implementation-dependent ...)  and the particular stack used for any
operation is implied unambiguously by the operation being performed.
The stack used for all integer operations is called the "data stack"
and, since this is the stack used most commonly, references to "the data
stack" are often abbreviated to "the stack".

   The stacks have a last-in, first-out (LIFO) organisation.  If you
type:

     1 2 3<RET>  ok

   Then this instructs the text interpreter to placed three numbers on
the (data) stack.  An analogy for the behaviour of the stack is to take
a pack of playing cards and deal out the ace (1), 2 and 3 into a pile on
the table.  The 3 was the last card onto the pile ("last-in") and if you
take a card off the pile then, unless you're prepared to fiddle a bit,
the card that you take off will be the 3 ("first-out").  The number that
will be first-out of the stack is called the "top of stack", which is
often abbreviated to "TOS".

   To understand how parameters are passed in Forth, consider the
behaviour of the definition '+' (pronounced "plus").  You will not be
surprised to learn that this definition performs addition.  More
precisely, it adds two numbers together and produces a result.  Where
does it get the two numbers from?  It takes the top two numbers off the
stack.  Where does it place the result?  On the stack.  You can act out
the behaviour of '+' with your playing cards like this:

   * Pick up two cards from the stack on the table
   * Stare at them intently and ask yourself "what is the sum of these
     two numbers"
   * Decide that the answer is 5
   * Shuffle the two cards back into the pack and find a 5
   * Put a 5 on the remaining ace that's on the table.

   If you don't have a pack of cards handy but you do have Forth
running, you can use the definition '.s' to show the current state of
the stack, without affecting the stack.  Type:

     clearstacks 1 2 3<RET> ok
     .s<RET> <3> 1 2 3  ok

   The text interpreter looks up the word 'clearstacks' and executes it;
it tidies up the stacks (data and floating point stack) and removes any
entries that may have been left on them by earlier examples.  The text
interpreter pushes each of the three numbers in turn onto the stack.
Finally, the text interpreter looks up the word '.s' and executes it.
The effect of executing '.s' is to print the "<3>" (the total number of
items on the stack) followed by a list of all the items on the stack;
the item on the far right-hand side is the TOS.

   You can now type:

     + .s<RET> <2> 1 5  ok

which is correct; there are now 2 items on the stack and the result of
the addition is 5.

   If you're playing with cards, try doing a second addition: pick up
the two cards, work out that their sum is 6, shuffle them into the pack,
look for a 6 and place that on the table.  You now have just one item on
the stack.  What happens if you try to do a third addition?  Pick up the
first card, pick up the second card -- ah!  There is no second card.
This is called a "stack underflow" and consitutes an error.  If you try
to do the same thing with Forth it often reports an error (probably a
Stack Underflow or an Invalid Memory Address error).

   The opposite situation to a stack underflow is a "stack overflow",
which simply accepts that there is a finite amount of storage space
reserved for the stack.  To stretch the playing card analogy, if you had
enough packs of cards and you piled the cards up on the table, you would
eventually be unable to add another card; you'd hit the ceiling.  Gforth
allows you to set the maximum size of the stacks.  In general, the only
time that you will get a stack overflow is because a definition has a
bug in it and is generating data on the stack uncontrollably.

   There's one final use for the playing card analogy.  If you model
your stack using a pack of playing cards, the maximum number of items on
your stack will be 52 (I assume you didn't use the Joker).  The maximum
value of any item on the stack is 13 (the King).  In fact, the only
possible numbers are positive integer numbers 1 through 13; you can't
have (for example) 0 or 27 or 3.52 or -2.  If you change the way you
think about some of the cards, you can accommodate different numbers.
For example, you could think of the Jack as representing 0, the Queen as
representing -1 and the King as representing -2.  Your range remains
unchanged (you can still only represent a total of 13 numbers) but the
numbers that you can represent are -2 through 10.

   In that analogy, the limit was the amount of information that a
single stack entry could hold, and Forth has a similar limit.  In Forth,
the size of a stack entry is called a "cell".  The actual size of a cell
is implementation dependent and affects the maximum value that a stack
entry can hold.  A Standard Forth provides a cell size of at least
16-bits, and most desktop systems use a cell size of 32-bits.

   Forth does not do any type checking for you, so you are free to
manipulate and combine stack items in any way you wish.  A convenient
way of treating stack items is as 2's complement signed integers, and
that is what Standard words like '+' do.  Therefore you can type:

     -5 12 + .s<RET> <1> 7  ok

   If you use numbers and definitions like '+' in order to turn Forth
into a great big pocket calculator, you will realise that it's rather
different from a normal calculator.  Rather than typing 2 + 3 = you had
to type 2 3 + (ignore the fact that you had to use '.s' to see the
result).  The terminology used to describe this difference is to say
that your calculator uses "Infix Notation" (parameters and operators are
mixed) whilst Forth uses "Postfix Notation" (parameters and operators
are separate), also called "Reverse Polish Notation".

   Whilst postfix notation might look confusing to begin with, it has
several important advantages:

   * it is unambiguous
   * it is more concise
   * it fits naturally with a stack-based system

   To examine these claims in more detail, consider these sums:

     6 + 5 * 4 =
     4 * 5 + 6 =

   If you're just learning maths or your maths is very rusty, you will
probably come up with the answer 44 for the first and 26 for the second.
If you are a bit of a whizz at maths you will remember the convention
that multiplication takes precendence over addition, and you'd come up
with the answer 26 both times.  To explain the answer 26 to someone who
got the answer 44, you'd probably rewrite the first sum like this:

     6 + (5 * 4) =

   If what you really wanted was to perform the addition before the
multiplication, you would have to use parentheses to force it.

   If you did the first two sums on a pocket calculator you would
probably get the right answers, unless you were very cautious and
entered them using these keystroke sequences:

   6 + 5 = * 4 = 4 * 5 = + 6 =

   Postfix notation is unambiguous because the order that the operators
are applied is always explicit; that also means that parentheses are
never required.  The operators are active (the act of quoting the
operator makes the operation occur) which removes the need for "=".

   The sum 6 + 5 * 4 can be written (in postfix notation) in two
equivalent ways:

     6 5 4 * +      or:
     5 4 * 6 +

   An important thing that you should notice about this notation is that
the order of the numbers does not change; if you want to subtract 2 from
10 you type '10 2 -'.

   The reason that Forth uses postfix notation is very simple to
explain: it makes the implementation extremely simple, and it follows
naturally from using the stack as a mechanism for passing parameters.
Another way of thinking about this is to realise that all Forth
definitions are active; they execute as they are encountered by the text
interpreter.  The result of this is that the syntax of Forth is
trivially simple.

4.3 Your first Forth definition
===============================

Until now, the examples we've seen have been trivial; we've just been
using Forth as a bigger-than-pocket calculator.  Also, each calculation
we've shown has been a "one-off" -- to repeat it we'd need to type it in
again(1) In this section we'll see how to add new words to Forth's
vocabulary.

   The easiest way to create a new word is to use a "colon definition".
We'll define a few and try them out before worrying too much about how
they work.  Try typing in these examples; be careful to copy the spaces
accurately:

     : add-two 2 + . ;
     : greet ." Hello and welcome" ;
     : demo 5 add-two ;

Now try them out:

     greet<RET> Hello and welcome  ok
     greet greet<RET> Hello and welcomeHello and welcome  ok
     4 add-two<RET> 6  ok
     demo<RET> 7  ok
     9 greet demo add-two<RET> Hello and welcome7 11  ok

   The first new thing that we've introduced here is the pair of words
':' and ';'.  These are used to start and terminate a new definition,
respectively.  The first word after the ':' is the name for the new
definition.

   As you can see from the examples, a definition is built up of words
that have already been defined; Forth makes no distinction between
definitions that existed when you started the system up, and those that
you define yourself.

   The examples also introduce the words '.' (dot), '."' (dot-quote) and
'dup' (dewp).  Dot takes the value from the top of the stack and
displays it.  It's like '.s' except that it only displays the top item
of the stack and it is destructive; after it has executed, the number is
no longer on the stack.  There is always one space printed after the
number, and no spaces before it.  Dot-quote defines a string (a sequence
of characters) that will be printed when the word is executed.  The
string can contain any printable characters except '"'.  A '"' has a
special function; it is not a Forth word but it acts as a delimiter (the
way that delimiters work is described in the next section).  Finally,
'dup' duplicates the value at the top of the stack.  Try typing '5 dup
.s' to see what it does.

   We already know that the text interpreter searches through the
dictionary to locate names.  If you've followed the examples earlier,
you will already have a definition called 'add-two'.  Lets try modifying
it by typing in a new definition:

     : add-two dup . ." + 2 = " 2 + . ;<RET> redefined add-two  ok

   Forth recognised that we were defining a word that already exists,
and printed a message to warn us of that fact.  Let's try out the new
definition:

     9 add-two<RET> 9 + 2 = 11  ok

All that we've actually done here, though, is to create a new
definition, with a particular name.  The fact that there was already a
definition with the same name did not make any difference to the way
that the new definition was created (except that Forth printed a warning
message).  The old definition of add-two still exists (try 'demo' again
to see that this is true).  Any new definition will use the new
definition of 'add-two', but old definitions continue to use the version
that already existed at the time that they were 'compiled'.

   Before you go on to the next section, try defining and redefining
some words of your own.

   ---------- Footnotes ----------

   (1) That's not quite true.  If you press the up-arrow key on your
keyboard you should be able to scroll back to any earlier command, edit
it and re-enter it.

4.4 How does that work?
=======================

Now we're going to take another look at the definition of 'add-two' from
the previous section.  From our knowledge of the way that the text
interpreter works, we would have expected this result when we tried to
define 'add-two':

     : add-two 2 + . ;<RET>
     *the terminal*:4: Undefined word
     : >>>add-two<<< 2 + . ;

   The reason that this didn't happen is bound up in the way that ':'
works.  The word ':' does two special things.  The first special thing
that it does is to prevent the text interpreter from ever seeing the
characters 'add-two'.  The text interpreter uses a variable called '>IN'
(pronounced "to-in") to keep track of where it is in the input line.
When it encounters the word ':' it behaves in exactly the same way as it
does for any other word; it looks it up in the name dictionary, finds
its xt and executes it.  When ':' executes, it looks at the input
buffer, finds the word 'add-two' and advances the value of '>IN' to
point past it.  It then does some other stuff associated with creating
the new definition (including creating an entry for 'add-two' in the
name dictionary).  When the execution of ':' completes, control returns
to the text interpreter, which is oblivious to the fact that it has been
tricked into ignoring part of the input line.

   Words like ':' -- words that advance the value of '>IN' and so prevent
the text interpreter from acting on the whole of the input line -- are
called "parsing words".

   The second special thing that ':' does is change the value of a
variable called 'state', which affects the way that the text interpreter
behaves.  When Gforth starts up, 'state' has the value 0, and the text
interpreter is said to be "interpreting".  During a colon definition
(started with ':'), 'state' is set to -1 and the text interpreter is
said to be "compiling".

   In this example, the text interpreter is compiling when it processes
the string "'2 + . ;'".  It still breaks the string down into character
sequences in the same way.  However, instead of pushing the number '2'
onto the stack, it lays down ("compiles") some magic into the definition
of 'add-two' that will make the number '2' get pushed onto the stack
when 'add-two' is "executed".  Similarly, the behaviours of '+' and '.'
are also compiled into the definition.

   Certain kinds of words do not get compiled.  These so-called
"immediate words" get executed (performed now) regardless of whether the
text interpreter is interpreting or compiling.  The word ';' is an
immediate word.  Rather than being compiled into the definition, it
executes.  Its effect is to terminate the current definition, which
includes changing the value of 'state' back to 0.

   When you execute 'add-two', it has a "run-time effect" that is
exactly the same as if you had typed '2 + . <RET>' outside of a
definition.

   In Forth, every word or number can be described in terms of two
properties:

   * Its "interpretation semantics" describe how it will behave when the
     text interpreter encounters it in "interpret" state.  The
     interpretation semantics of a word are represented by its
     "execution token" (*note Execution token::).
   * Its "compilation semantics" describe how it will behave when the
     text interpreter encounters it in "compile" state.  The compilation
     semantics of a word are represented by its "compilation token"
     (*note Compilation token::).

Numbers are always treated in a fixed way:

   * When the number is "interpreted", its behaviour is to push the
     number onto the stack.
   * When the number is "compiled", a piece of code is appended to the
     current definition that pushes the number when it runs.  (In other
     words, the compilation semantics of a number are to postpone its
     interpretation semantics until the run-time of the definition that
     it is being compiled into.)

   Words don't always behave in such a regular way, but most have
default semantics which means that they behave like this:

   * The "interpretation semantics" of the word are to do something
     useful.
   * The "compilation semantics" of the word are to append its
     "interpretation semantics" to the current definition (so that its
     run-time behaviour is to do something useful).

   The actual behaviour of any particular word can be controlled by
using the words 'immediate' and 'compile-only' when the word is defined.
These words set flags in the name dictionary entry of the most recently
defined word, and these flags are retrieved by the text interpreter when
it finds the word in the name dictionary.

   A word that is marked as "immediate" has compilation semantics that
are identical to its interpretation semantics.  In other words, it
behaves like this:

   * The "interpretation semantics" of the word are to do something
     useful.
   * The "compilation semantics" of the word are to do something useful
     (and actually the same thing); i.e., it is executed during
     compilation.

   Marking a word as "compile-only" means that the text interpreter
produces a warning when encountering this word in interpretation state;
ticking the word (with ''' or '[']' also produces a warning.

   It is never necessary to use 'compile-only' (and it is not even part
of Standard Forth, though it is provided by many implementations) but it
is good etiquette to apply it to a word that will not behave correctly
(and might have unexpected side-effects) in interpret state.  For
example, it is only legal to use the conditional word 'IF' within a
definition.  If you forget this and try to use it elsewhere, the fact
that (in Gforth) it is marked as 'compile-only' allows the text
interpreter to generate a helpful warning.

   This example shows the difference between an immediate and a
non-immediate word:

     : show-state state @ . ;
     : show-state-now show-state ; immediate
     : word1 show-state ;
     : word2 show-state-now ;

   The word 'immediate' after the definition of 'show-state-now' makes
that word an immediate word.  These definitions introduce a new word:
'@' (pronounced "fetch").  This word fetches the value of a variable,
and leaves it on the stack.  Therefore, the behaviour of 'show-state' is
to print a number that represents the current value of 'state'.

   When you execute 'word1', it prints the number 0, indicating that the
system is interpreting.  When the text interpreter compiled the
definition of 'word1', it encountered 'show-state' whose compilation
semantics are to append its interpretation semantics to the current
definition.  When you execute 'word1', it performs the interpretation
semantics of 'show-state'.  At the time that 'word1' (and therefore
'show-state') is executed, the system is interpreting.

   When you pressed <RET> after entering the definition of 'word2', you
should have seen the number -1 printed, followed by "' ok'".  When the
text interpreter compiled the definition of 'word2', it encountered
'show-state-now', an immediate word, whose compilation semantics are
therefore to perform its interpretation semantics.  It is executed
straight away (even before the text interpreter has moved on to process
another group of characters; the ';' in this example).  The effect of
executing it is to display the value of 'state' at the time that the
definition of 'word2' is being defined.  Printing -1 demonstrates that
the system is compiling at this time.  If you execute 'word2' it does
nothing at all.

   Before leaving the subject of immediate words, consider the behaviour
of '."' in the definition of 'greet', in the previous section.  This
word is both a parsing word and an immediate word.  Notice that there is
a space between '."' and the start of the text 'Hello and welcome', but
that there is no space between the last letter of 'welcome' and the '"'
character.  The reason for this is that '."' is a Forth word; it must
have a space after it so that the text interpreter can identify it.  The
'"' is not a Forth word; it is a "delimiter".  The examples earlier show
that, when the string is displayed, there is neither a space before the
'H' nor after the 'e'.  Since '."' is an immediate word, it executes at
the time that 'greet' is defined.  When it executes, its behaviour is to
search forward in the input line looking for the delimiter.  When it
finds the delimiter, it updates '>IN' to point past the delimiter.  It
also compiles some magic code into the definition of 'greet'; the xt of
a run-time routine that prints a text string.  It compiles the string
'Hello and welcome' into memory so that it is available to be printed
later.  When the text interpreter gains control, the next word it finds
in the input stream is ';' and so it terminates the definition of
'greet'.

4.5 Forth is written in Forth
=============================

When you start up a Forth compiler, a large number of definitions
already exist.  In Forth, you develop a new application using bottom-up
programming techniques to create new definitions that are defined in
terms of existing definitions.  As you create each definition you can
test and debug it interactively.

   If you have tried out the examples in this section, you will probably
have typed them in by hand; when you leave Gforth, your definitions will
be lost.  You can avoid this by using a text editor to enter Forth
source code into a file, and then loading code from the file using
'include' (*note Forth source files::).  A Forth source file is
processed by the text interpreter, just as though you had typed it in by
hand(1).

   Gforth also supports the traditional Forth alternative to using text
files for program entry (*note Blocks::).

   In common with many, if not most, Forth compilers, most of Gforth is
actually written in Forth.  All of the '.fs' files in the installation
directory(2) are Forth source files, which you can study to see examples
of Forth programming.

   Gforth maintains a history file that records every line that you type
to the text interpreter.  This file is preserved between sessions, and
is used to provide a command-line recall facility.  If you enter long
definitions by hand, you can use a text editor to paste them out of the
history file into a Forth source file for reuse at a later time (for
more information *note Command-line editing::).

   ---------- Footnotes ----------

   (1) Actually, there are some subtle differences -- see *note The Text
Interpreter::.

   (2) For example, '/usr/local/share/gforth...'

4.6 Review - elements of a Forth system
=======================================

To summarise this chapter:

   * Forth programs use "factoring" to break a problem down into small
     fragments called "words" or "definitions".
   * Forth program development is an interactive process.
   * The main command loop that accepts input, and controls both
     interpretation and compilation, is called the "text interpreter"
     (also known as the "outer interpreter").
   * Forth has a very simple syntax, consisting of words and numbers
     separated by spaces or carriage-return characters.  Any additional
     syntax is imposed by "parsing words".
   * Forth uses a stack to pass parameters between words.  As a result,
     it uses postfix notation.
   * To use a word that has previously been defined, the text
     interpreter searches for the word in the "name dictionary".
   * Words have "interpretation semantics" and "compilation semantics".
   * The text interpreter uses the value of 'state' to select between
     the use of the "interpretation semantics" and the "compilation
     semantics" of a word that it encounters.
   * The relationship between the "interpretation semantics" and
     "compilation semantics" for a word depends upon the way in which
     the word was defined (for example, whether it is an "immediate"
     word).
   * Forth definitions can be implemented in Forth (called "high-level
     definitions") or in some other way (usually a lower-level language
     and as a result often called "low-level definitions", "code
     definitions" or "primitives").
   * Many Forth systems are implemented mainly in Forth.

4.7 Where To Go Next
====================

Amazing as it may seem, if you have read (and understood) this far, you
know almost all the fundamentals about the inner workings of a Forth
system.  You certainly know enough to be able to read and understand the
rest of this manual and the Standard Forth document, to learn more about
the facilities that Forth in general and Gforth in particular provide.
Even scarier, you know almost enough to implement your own Forth system.
However, that's not a good idea just yet...  better to try writing some
programs in Gforth.

   Forth has such a rich vocabulary that it can be hard to know where to
start in learning it.  This section suggests a few sets of words that
are enough to write small but useful programs.  Use the word index in
this document to learn more about each word, then try it out and try to
write small definitions using it.  Start by experimenting with these
words:

   * Arithmetic: '+ - * / /MOD */ ABS INVERT'
   * Comparison: 'MIN MAX ='
   * Logic: 'AND OR XOR NOT'
   * Stack manipulation: 'DUP DROP SWAP OVER'
   * Loops and decisions: 'IF ELSE ENDIF ?DO I LOOP'
   * Input/Output: '. ." EMIT CR KEY'
   * Defining words: ': ; CREATE'
   * Memory allocation words: 'ALLOT ,'
   * Tools: 'SEE WORDS .S MARKER'

   When you have mastered those, go on to:

   * More defining words: 'VARIABLE CONSTANT VALUE TO CREATE DOES>'
   * Memory access: '@ !'

   When you have mastered these, there's nothing for it but to read
through the whole of this manual and find out what you've missed.

4.8 Exercises
=============

TODO: provide a set of programming excercises linked into the stuff done
already and into other sections of the manual.  Provide solutions to all
the exercises in a .fs file in the distribution.

5 Literals in source code
*************************

To push an integer number on the data stack, you write the number in
source code, e.g., '123'.  You can prefix the digits with '-' to
indicate a negative number, e.g.  '-123'.  This works both inside colon
definitions and outside.  The number is interpreted according to the
value of 'base' (*note Number Conversion::).  The digits are '0' to '9'
and 'a' (decimal 10) to 'z' (decimal 35), but only digits smaller than
the base are recognized.  The conversion is case-insensitive, so 'A' and
'a' are the same digit.

   You can make the base explicit for the number by using a prefix:

   * '#' -- decimal
   * '%' -- binary
   * '$' -- hexadecimal
   * '&' -- decimal (non-standard)
   * '0x' -- hexadecimal, if base<33 (non-standard).

   For combinations including base-prefix and sign, the standard order
is to have the base-prefix first (e.g., '#-123'); Gforth supports both
orders.

   You can put a decimal point '.' at the end of a number (or,
non-standardly, anywhere else except before a prefix) to get a
double-cell integer (e.g., '#-123.' or '#-.123' (the same number)).  If
users experienced in another programming language see or write such a
number without base prefix (e.g., '-123.'), they may expect that the
number represents a floating-point value.  To clear up the confusion
early, Gforth warns of such usage; to avoid the warnings, the best
approach is to always write double numbers with a base prefix (e.g.,
'#-123.')

   Here are some examples, with the equivalent decimal number shown
after in braces:

   '$-41' (-65), '%1001101' (205), '%1001.0001' (145 - a
double-precision number), '#905' (905), '$abc' (2478), '$ABC' (2478).

   You can get the numeric value of a (character) code point by
surrounding the character with ''' (e.g., ''a'').  The trailing ''' is
required by the standard, but you can leave it away in Gforth.  Note
that this also works for non-ASCII characters.  For many uses, it is
more useful to have the character as a string rather than as a cell; see
below for the string syntax.

   For floating-point numbers in Forth, you recognize them due to their
exponent.  I.e.  '1.' is a double-cell integer, and '1e0' is a
floating-point number; the latter can be (and usually is) shortened to
'1e'.  Both the significand (the part before the 'e' or 'E') and the
exponent may have signs (including '+'); the significand must contain at
least one digit and may contain a decimal point, the exponent can be
empty.  Floating-point numbers always use decimal base for both
significand and exponent, and are only recognized when the base is
decimal.  Examples are: '1e 1e0 1.e 1.e0 +1e+0' (which all represent the
same number) '+12.E-4'.

   A Gforth extension (since 1.0) is to write a floating-point number in
scaled notation: It can optionally have a sign, then one or more digits,
then use one of the mostly SI-defined scaling symbols (aka metric
prefixes) or '%', and then optionally more digits.  Here's the full list
of scaling symbols that Gforth accepts:

   * 'Q' 'e30' quetta
   * 'R' 'e27' ronna
   * 'Y' 'e24' yotta
   * 'Z' 'e21' zetta
   * 'X' 'e18' exa (not 'E')
   * 'P' 'e15' peta
   * 'T' 'e12' tera
   * 'G' 'e9' giga
   * 'M' 'e6' mega
   * 'k' 'e3' kilo
   * 'h' 'e2' hecto
   * 'd' 'e-1' deci
   * '%' 'e-2' percent (not 'c')
   * 'm' 'e-3' milli
   * 'u' 'e-6' micro (not 'μ')
   * 'n' 'e-9' nano
   * 'p' 'e-12' pico
   * 'f' 'e-15' femto
   * 'a' 'e-18' atto
   * 'z' 'e-21' zepto
   * 'y' 'e-24' yocto
   * 'r' 'e-27' ronto
   * 'q' 'e-30' quecto

   Unlike most of the rest of Gforth, scaling symbols are treated
case-sensitively.  Using the scaled notation is equivalent to using a
decimal point instead of the scaling symbol and appending the
exponential notation at the end.  Examples of scaled notation: '6k5'
(6500e) '23%' (0.23e).

   You can input a string by surrounding it with '"' (e.g.  '"abc"', '"a
b"').  The result is the starting address and byte (=char) count of the
string on the data stack.

   You have to escape any '"' inside the string with '\' (e.g.,
'"double-quote->\"<-"').  In addition, this string syntax supports all
the ways to write control characters that are supported by 's\"' (*note
String and character literals::).  A disadvantage of this string syntax
is that it is non-standard; for standard programs, use 's\"' instead.

   You can input an environment variable by first loading 'rec-env.fs'
and then prefixing the environment variable with '$', e.g., '$HOME'; the
result is a string descriptor on the data stack in the format described
above.  This is equivalent to '"HOME" getenv', i.e., the environment
variable is resolved at run-time.

   You can input an execution token (xt) of a word by prefixing the name
of the word with '`' (e.g., '`dup').  An advantage over using ''' or
'[']' is you do not need to switch between them when copying and pasting
code from inside to outside a colon definition or vice versa.  A
disadvantage is that this syntax is non-standard.

   You can input a name token (nt) of a word by prefixing the name of
the word with '``' (e.g., '``dup').  This syntax is also non-standard.

   You can input a body address of a word by surrounding it with '<' and
'>' (e.g., '<spaces>').  You can also input an address that is at a
positive offset from the body address (typically an address in that
body), by putting '+' and a number (see syntax above) between the word
name and the closing '>' (e.g., '<spaces+$15>', 'spaces+-3').  You will
get the body address plus the number.  This non-standard feature exists
to allow copying and pasting the output of '...' (*note Examining
data::).

6 Forth Words
*************

6.1 Notation
============

The Forth words are described in this section in the glossary notation
that has become a de-facto standard for Forth texts:

word     Stack effect   wordset   pronunciation
   Description

WORD
     The name of the word.

STACK EFFECT
     The stack effect is written in the notation 'before -- after',
     where before and after describe the top of stack entries before and
     after the execution of the word.  The rest of the stack is not
     touched by the word.  The top of stack is rightmost, i.e., a stack
     sequence is written as it is typed in.  Note that Gforth uses a
     separate floating point stack, but a unified stack notation.  Also,
     return stack effects are not shown in stack effect, but in
     Description.  The name of a stack item describes the type and/or
     the function of the item.  See below for a discussion of the types.

     All words have two stack effects: A compile-time stack effect and a
     run-time stack effect.  The compile-time stack-effect of most words
     is -- .  If the compile-time stack-effect of a word deviates from
     this standard behaviour, or the word does other unusual things at
     compile time, both stack effects are shown; otherwise only the
     run-time stack effect is shown.

     Also note that in code templates or examples there can be comments
     in parentheses that display the stack picture at this point; there
     is no '--' in these places, because there is no before-after
     situation.

PRONUNCIATION
     How the word is pronounced.

WORDSET
     The wordset specifies whether a word has been standardized, it is
     an environmental query string, or if it is a Gforth-specific word.
     In the latter case the wordset contains the string 'gforth', other
     wordset names are either 'environment' of refer to standard word
     sets.

     The Forth standard is divided into several word sets.  In theory, a
     standard system need not support all of them, but in practice,
     serious systems on non-tiny machines support almost all
     standardized words (some systems require explicit loading of some
     word sets, however), so it does not increase portability in
     practice to be parsimonious in using word sets.

     For the Gforth-specific words, we have the following categories:

     'gforth'
     'gforth-<version>'
          We intend to permanently support this word in Gforth and it
          has been available since Gforth <version> (possibly not as
          supported word at that time).

     'gforth-experimental'
          This word is available in the present version and may turn
          into a permanent word or may be removed in a future release of
          Gforth.  Feedback welcome.

     'gforth-internal'
          This word is an internal factor, not a supported word, and it
          may be removed in a future release of Gforth.

     'gforth-obsolete'
          This word will be removed in a future release of Gforth.

DESCRIPTION
     A description of the behaviour of the word.

   The type of a stack item is specified by the character(s) the name
starts with:

'f'
     Boolean flags, i.e.  'false' or 'true'.
'c'
     Char
'w'
     Cell, can contain an integer or an address
'n'
     signed integer
'u'
     unsigned integer
'd'
     double sized signed integer
'ud'
     double sized unsigned integer
'r'
     Float (on the FP stack)
'a-'
     Cell-aligned address
'c-'
     Char-aligned address (note that a Char may have two bytes in
     Windows NT)
'f-'
     Float-aligned address
'df-'
     Address aligned for IEEE double precision float
'sf-'
     Address aligned for IEEE single precision float
'xt'
     Execution token, same size as Cell
'wid'
     Word list ID, same size as Cell
'ior, wior'
     I/O result code, cell-sized.  In Gforth, you can 'throw' iors.
'f83name'
     Pointer to a name structure
'"'
     string in the input stream (not on the stack).  The terminating
     character is a blank by default.  If it is not a blank, it is shown
     in '<>' quotes.

6.2 Case insensitivity
======================

Gforth is case-insensitive; you can enter definitions and invoke
Standard words using upper, lower or mixed case (however, *note
Implementation-defined options: core-idef.).

   Standard Forth only requires implementations to recognise Standard
words when they are typed entirely in upper case.  Therefore, a Standard
program must use upper case for all Standard words.  You can use
whatever case you like for words that you define, but in a Standard
program you have to use the words in the same case that you defined
them.

   Gforth supports case sensitivity through 'cs-wordlist's
(case-sensitive wordlists, *note Word Lists::).

   Two people have asked how to convert Gforth to be case-sensitive;
while we think this is a bad idea, you can change all wordlists into
tables like this:

     ' table-find forth-wordlist wordlist-map  !

   Note that you now have to type the predefined words in the same case
that we defined them, which are varying.  You may want to convert them
to your favourite case before doing this operation (I won't explain how,
because if you are even contemplating doing this, you'd better have
enough knowledge of Forth systems to know this already).

6.3 Comments
============

Forth supports two styles of comment; the traditional in-line comment,
'(' and its modern cousin, the comment to end of line; '\'.

'(' ( compilation 'ccc<close-paren>' -- ; run-time --  ) core,file "paren"
   Comment, usually till the next ')': parse and discard all subsequent
characters in the parse area until ")" is encountered.  During
interactive input, an end-of-line also acts as a comment terminator.
For file input, it does not; if the end-of-file is encountered whilst
parsing for the ")" delimiter, Gforth will generate a warning.

'\' ( compilation 'ccc<newline>' -- ; run-time --  ) core-ext,block-ext "backslash"
   Comment until the end of line: parse and discard all remaining
characters in the parse area, except while 'load'ing from a block: while
'load'ing from a block, parse and discard all remaining characters in
the 64-byte line.

'\G' ( compilation 'ccc<newline>' -- ; run-time --  ) gforth-0.2 "backslash-gee"
   Equivalent to '\' but used as a tag to annotate definition comments
into documentation.

6.4 Boolean Flags
=================

A Boolean flag is cell-sized.  A cell with all bits clear represents the
flag 'false' and a flag with all bits set represents the flag 'true'.
Words that check a flag (for example, 'IF') will treat a cell that has
any bit set as 'true'.

'true' ( -- f  ) core-ext "true"
   'Constant' -- f is a cell with all bits set.

'false' ( -- f  ) core-ext "false"
   'Constant' -- f is a cell with all bits clear.

'on' ( a-addr --  ) gforth-0.2 "on"
   Set the (value of the) variable at a-addr to 'true'.

'off' ( a-addr --  ) gforth-0.2 "off"
   Set the (value of the) variable at a-addr to 'false'.

'select' ( u1 u2 f -- u ) gforth-1.0 "select"
   If f is false, u is u2, otherwise u1.

6.5 Arithmetic
==============

Forth arithmetic is not checked, i.e., you will not hear about integer
overflow on addition or multiplication, you may hear about division by
zero if you are lucky.  The operator is written after the operands, but
the operands are still in the original order.  I.e., the infix '2-1'
corresponds to '2 1 -'.  Forth offers a variety of division operators.
If you perform division with potentially negative operands, you do not
want to use '/' or '/mod' with its implementation-defined behaviour,
but, e.g., '/f', '/modf' or 'fm/mod' (*note Integer division::).

6.5.1 Single precision
----------------------

By default, numbers in Forth are single-precision integers that are one
cell in size.  They can be signed or unsigned, depending upon how you
treat them.  For the rules used by the text interpreter for recognising
single-precision integers see *note Number Conversion::.

   These words are all defined for signed operands, but some of them
also work for unsigned numbers: '+', '1+', '-', '1-', '*'.

'+' ( n1 n2 -- n ) core "plus"

'1+' ( n1 -- n2 ) core "one-plus"

'under+' ( n1 n2 n3 -- n n2 ) gforth-0.3 "under-plus"
   add n3 to n1 (giving n)

'-' ( n1 n2 -- n ) core "minus"

'1-' ( n1 -- n2 ) core "one-minus"

'*' ( n1 n2 -- n ) core "star"

'negate' ( n1 -- n2 ) core "negate"

'abs' ( n -- u ) core "abs"

'min' ( n1 n2 -- n ) core "min"

'max' ( n1 n2 -- n ) core "max"

'umin' ( u1 u2 -- u ) gforth-0.5 "umin"

'umax' ( u1 u2 -- u ) gforth-1.0 "umax"

6.5.2 Double precision
----------------------

For the rules used by the text interpreter for recognising
double-precision integers, see *note Number Conversion::.

   A double precision number is represented by a cell pair, with the
most significant cell at the TOS. It is trivial to convert an unsigned
single to a double: simply push a '0' onto the TOS. Since numbers are
represented by Gforth using 2's complement arithmetic, converting a
signed single to a (signed) double requires sign-extension across the
most significant cell.  This can be achieved using 's>d'.  The moral of
the story is that you cannot convert a number without knowing whether it
represents an unsigned or a signed number.

   These words are all defined for signed operands, but some of them
also work for unsigned numbers: 'd+', 'd-'.

's>d' ( n -- d  ) core "s-to-d"

'd>s' ( d -- n  ) double "d-to-s"

'd+' ( ud1 ud2 -- ud ) double "d-plus"

'd-' ( d1 d2 -- d ) double "d-minus"

'dnegate' ( d1 -- d2 ) double "d-negate"

'dabs' ( d -- ud  ) double "d-abs"

'dmin' ( d1 d2 -- d  ) double "d-min"

'dmax' ( d1 d2 -- d  ) double "d-max"

6.5.3 Mixed precision
---------------------

'm+' ( d1 n -- d2 ) double "m-plus"

'm*' ( n1 n2 -- d ) core "m-star"

'um*' ( u1 u2 -- ud ) core "u-m-star"

6.5.4 Integer division
----------------------

Below you find a considerable number of words for dealing with
divisions.  A major difference between them is in dealing with signed
division: Do the words support signed division (those with the 'U'
prefix do not)?

   If they do, do they round towards negative infinity (floored
division, suffix 'F'), or towards 0 (symmetric division, suffix 'S').
The standard leaves the issue implementation-defined for most standard
words ('/ mod /mod */ */mod m*/'), and different systems have made
different choices.  Gforth implements these words as floored (since
Gforth 0.7).  There is only a difference between floored and symmetric
division if the dividend and the divisor have different signs, and the
dividend is not a multiple of the divisor.  The following table
illustrates the results:

                           floored          symmetric
     dividend divisor remainder quotient remainder quotient
         10      7           3   1              3   1
        -10      7           4  -2             -3  -1
         10     -7          -4  -2              3  -1
        -10     -7          -3   1             -3   1

   The common case where floored vs. symmetric makes a difference is
when dividends n1 with varying sign are divided by the same positive
divisor n2; in that case you usually want floored division, because then
the remainder is always positive and does not change sign depending on
the dividend; also, with floored division, the quotient always increases
by 1 when n1 increases by n2, while with symmetric division there is no
increase in the quotient for -n2<n1<n2 (the quotient is 0 in this
range).

   In any case, if you divide numbers where floored vs. symmetric makes
a difference, you should think about which variant is the right one for
you, and then use either the appropriately suffixed Gforth words, or the
standard words 'fm/mod' or 'sm/rem'.

   Single-by-single-cell division:

'/' ( n1 n2 -- n  ) core "slash"
   n=n1/n2

'/s' ( n1 n2 -- n ) gforth-1.0 "slash-s"

'/f' ( n1 n2 -- n ) gforth-1.0 "slash-f"

'u/' ( u1 u2 -- u ) gforth-1.0 "u-slash"

'mod' ( n1 n2 -- n  ) core "mod"
   n is the modulus of n1/n2

'mods' ( n1 n2 -- n ) gforth-1.0 "mod-s"

'modf' ( n1 n2 -- n ) gforth-1.0 "modf"

'umod' ( u1 u2 -- u ) gforth-1.0 "umod"

'/mod' ( n1 n2 -- n3 n4  ) core "slash-mod"
   n1=n2*n4+n3; n3 is the modulus, n4 the quotient.

'/mods' ( n1 n2 -- n3 n4 ) gforth-1.0 "slash-mod-s"
   n3 is the remainder, n4 the quotient

'/modf' ( n1 n2 -- n3 n4 ) gforth-1.0 "slash-mod-f"
   n3 is the modulus, n4 the quotient

'u/mod' ( u1 u2 -- u3 u4 ) gforth-1.0 "u-slash-mod"
   u3 is the modulus, u4 the quotient

   Double-by-single-cell division with single-cell results; these words
are roughly as fast as the words above on some architectures (e.g.,
AMD64), but much slower on others (e.g., an order of magnitude on
various Aarch64 CPUs).

'fm/mod' ( d1 n1 -- n2 n3 ) core "f-m-slash-mod"
   Floored division: d1 = n3*n1+n2, n1>n2>=0 or 0>=n2>n1.

'sm/rem' ( d1 n1 -- n2 n3 ) core "s-m-slash-rem"
   Symmetric division: d1 = n3*n1+n2, sign(n2)=sign(d1) or 0.

'um/mod' ( ud u1 -- u2 u3 ) core "u-m-slash-mod"
   ud=u3*u1+u2, 0<=u2<u1

'du/mod' ( d u -- n u1 ) gforth-1.0 "du-slash-mod"
   d=n*u+u1, 0<=u1<u; PolyForth style mixed division

'*/' ( ( n1 n2 n3 -- n4  ) core "star-slash"
   n4=(n1*n2)/n3, with the intermediate result being double

'*/s' ( n1 n2 n3 -- n4 ) gforth-1.0 "star-slash-s"
   n4=(n1*n2)/n3, with the intermediate result being double

'*/f' ( n1 n2 n3 -- n4 ) gforth-1.0 "star-slash-f"
   n4=(n1*n2)/n3, with the intermediate result being double

'u*/' ( u1 u2 u3 -- u4 ) gforth-1.0 "u-star-slash"
   u4=(u1*u2)/u3, with the intermediate result being double.

'*/mod' ( n1 n2 n3 -- n4 n5  ) core "star-slash-mod"
   n1*n2=n3*n5+n4, with the intermediate result (n1*n2) being double; n4
is the modulus, n5 the quotient.

'*/mods' ( n1 n2 n3 -- n4 n5 ) gforth-1.0 "star-slash-mod-s"
   n1*n2=n3*n5+n4, with the intermediate result (n1*n2) being double; n4
is the remainder, n5 the quotient

'*/modf' ( n1 n2 n3 -- n4 n5 ) gforth-1.0 "star-slash-mod-f"
   n1*n2=n3*n5+n4, with the intermediate result (n1*n2) being double; n4
is the modulus, n5 the quotient

'u*/mod' ( u1 u2 u3 -- u4 u5 ) gforth-1.0 "u-star-slash-mod"
   u1*u2=u3*u5+u4, with the intermediate result (u1*u2) being double.

   Division with double-cell results; these words are much slower than
the words above.

'ud/mod' ( ud1 u2 -- urem udquot  ) gforth-0.2 "ud/mod"
   divide unsigned double ud1 by u2, resulting in a unsigned double
quotient udquot and a single remainder urem.

'm*/' ( d1 n2 u3 -- dquot  ) double "m-star-slash"
   dquot=(d1*n2)/u3, with the intermediate result being
triple-precision.  In ANS Forth u3 can only be a positive signed number.

   You can use the following environmental query 'floored' (*note
Environmental Queries::) to learn whether '/ mod /mod */ */mod m*/' use
floored or symmetric division.

   One other aspect of the integer division words is that most of them
can overflow, and division by zero is mathematically undefined.  What
happens if you hit one of these conditions depends on the engine, the
hardware, and the operating system: The engine 'gforth' tries hard to
throw the appropriate error -10 (Division by zero) or -11 (Result out of
range), but on some platforms throws -55 (Floating-point unidentified
fault).  The engine 'gforth-fast' may produce an inappropriate throw
code (and error message), or may produce no error, just produce a bogus
value.  I.e., you should not bet on such conditions being thrown, but
for quicker debugging 'gforth' catches more and produces more accurate
errors than 'gforth-fast'.

6.5.5 Two-stage integer division
--------------------------------

On most hardware, multiplication is significantly faster than division.
So if you have to divide many numbers by the same divisor, it is usually
faster to determine the reciprocal of the divisor once and multiply the
numbers with the reciprocal.  For integers, this is tricky, so Gforth
packages this work into the words described in this section.

   Let's start with an example: You want to divide all elements of an
array of cells by the same number n.  A straightforward way to implement
this is:

     : array/ ( addr u n -- )
       -rot cells bounds u+do
         i @ over / i !
       1 cells +loop
       drop ;

   A more efficient version looks like this:

     : array/ ( addr u n -- )
       {: | reci[ staged/-size ] :}
       reci[ /f-stage1m
       cells bounds u+do
         i @ reci[ /f-stage2m i !
       1 cells +loop ;

   This example first creates a local buffer 'reci[' with size
'staged/-size' for storing the reciprocal data.  Then '/f-stage1m'
computes the reciprocal of n and stores it in 'reci['.  Finally, inside
the loop '/f-stage2m' uses the data in 'reci[' to compute the quotient.

   There are some limitations: Only positive divisors are supported for
'/f-stage1m'; for 'u/-stage1m' you can use a divisor of 2 or higher.
You get an error if you try to use an unsupported divisor.  You must
initalize the reciprocal buffer for the floored second-stage words with
'/f-stage1m' and for the unsigned second-stage words with 'u/-stage1m'.
You must not modify the reciprocal buffer between the first stage and
the second stage; basically, don't treat it as a memory buffer, but as
something that is only mutable by the first stage; the point of this
rule is that future versions of Gforth will not consider aliasing of
this buffer.

   The words are:

'staged/-size' ( -- u  ) gforth-1.0 "staged-slash-size"
   Size of buffer for 'u/-stage1m' or '/f-stage1m'.

'/f-stage1m' ( n addr-reci --  ) gforth-1.0 "slash-f-stage1m"
   Compute the reciprocal of n and store it in the buffer addr-reci of
size 'staged/-size'.  Throws an error if n<1.

'/f-stage2m' ( n1 a-reci -- nquotient ) gforth-1.0 "slash-f-stage2m"
   Nquotient is the result of dividing n1 by the divisor represented by
a-reci, which was computed by '/f-stage1m'.

'modf-stage2m' ( n1 a-reci -- umodulus ) gforth-1.0 "mod-f-stage2m"
   Umodulus is the remainder of dividing n1 by the divisor represented
by a-reci, which was computed by '/f-stage1m'.

'/modf-stage2m' ( n1 a-reci -- umodulus nquotient ) gforth-1.0 "slash-mod-f-stage2m"
   Nquotient is the quotient and umodulus is the remainder of dividing
n1 by the divisor represented by a-reci, which was computed by
'/f-stage1m'.

'u/-stage1m' ( u addr-reci --  ) gforth-1.0 "u-slash-stage1m"
   Compute the reciprocal of u and store it in the buffer addr-reci of
size 'staged/-size'.  Throws an error if u<2.

'u/-stage2m' ( u1 a-reci -- uquotient ) gforth-1.0 "u-slash-stage2m"
   Uquotient is the result of dividing u1 by the divisor represented by
a-reci, which was computed by 'u/-stage1m'.

'umod-stage2m' ( u1 a-reci -- umodulus ) gforth-1.0 "u-mod-stage2m"
   Umodulus is the remainder of dividing u1 by the divisor represented
by a-reci, which was computed by 'u/-stage1m'.

'u/mod-stage2m' ( u1 a-reci -- umodulus uquotient ) gforth-1.0 "u-slash-mod-stage2m"
   Uquotient is the quotient and umodulus is the remainder of dividing
u1 by the divisor represented by a-reci, which was computed by
'u/-stage1m'.

   Gforth currently does not support staged symmetrical division.

   You can recover the divisor from (the address of) a reciprocal with
'staged/-divisor @':

'staged/-divisor' ( addr1 -- addr2  ) gforth-1.0 "staged-slash-divisor"
   Addr1 is the address of a reciprocal, addr2 is the address containing
the divisor from which the reciprocal was computed.

   This can be useful when looking at the decompiler output of Gforth: a
division by a constant is often compiled to a literal containing the
address of a reciprocal followed by a second-stage word.

   The performance impact of using these words strongly depends on the
architecture (does it have hardware division?)  and the specific
implementation (how fast is hardware division?), but just to give you an
idea about the relative performance of these words, here are the cycles
per iteration of a microbenchmark (which performs the mentioned word
once per iteration) on two AMD64 implementations; the norm column shows
the normal division word (e.g., 'u/'), while the stg2 column shows the
corresponding stage2 word (e.g., 'u/-stage2m'):

      Skylake              Zen2
     norm stg2           norm stg2
     41.3 15.8 u/	    35.2 21.4 u/
     39.8 19.7 umod	    36.9 25.8 umod
     44.0 25.3 u/mod	    43.0 33.9 u/mod
     48.7 16.9 /f	    36.2 22.5 /f
     47.9 20.5 modf	    37.9 27.1 modf
     53.0 24.6 /modf	    45.8 35.4 /modf
         227.2 u/stage1      101.9 u/stage1
         159.8 /fstage1       97.7 /fstage1

6.5.6 Bitwise operations
------------------------

'and' ( w1 w2 -- w ) core "and"

'or' ( w1 w2 -- w ) core "or"

'xor' ( w1 w2 -- w ) core "x-or"

'invert' ( w1 -- w2 ) core "invert"

'mux' ( u1 u2 u3 -- u ) gforth-1.0 "mux"
   Multiplex: For every bit in u3: for a 1 bit, select the corresponding
bit from u1, otherwise the corresponding bit from u2.  E.g., '%0011
%1100 %1010 mux' gives '%0110'

'lshift' ( u1 u -- u2 ) core "l-shift"
   Shift u1 left by u bits.

'rshift' ( u1 u -- u2 ) core "r-shift"
   Shift u1 (cell) right by u bits, filling the shifted-in bits with
zero (logical/unsigned shift).

'arshift' ( n1 u -- n2 ) gforth-1.0 "ar-shift"
   Shift n1 (cell) right by u bits, filling the shifted-in bits from the
sign bit of n1 (arithmetic shift).

'dlshift' ( ud1 u -- ud2 ) gforth-1.0 "dlshift"
   Shift ud1 (double-cell) left by u bits.

'drshift' ( ud1 u -- ud2 ) gforth-1.0 "drshift"
   Shift ud1 (double-cell) right by u bits, filling the shifted-in bits
with zero (logical/unsigned shift).

'darshift' ( d1 u -- d2 ) gforth-1.0 "darshift"
   Shift d1 (double-cell) right by u bits, filling the shifted-in bits
from the sign bit of d1 (arithmetic shift).

'2*' ( n1 -- n2 ) core "two-star"
   Shift left by 1; also works on unsigned numbers

'2/' ( n1 -- n2 ) core "two-slash"
   Arithmetic shift right by 1.  For signed numbers this is a floored
division by 2 (note that '/' not necessarily floors).

'd2*' ( d1 -- d2 ) double "d-two-star"
   Shift double-cell left by 1; also works on unsigned numbers

'd2/' ( d1 -- d2 ) double "d-two-slash"
   Arithmetic shift right by 1.  For signed numbers this is a floored
division by 2.

'>pow2' ( u1 -- u2 ) gforth-1.0 "to-pow2"
   u2 is the lowest power-of-2 number with u2>=u1.

'log2' ( u -- n ) gforth-1.0 "log2"
   N is the rounded-down binary logarithm of u, i.e., the index of the
first set bit; if u=0, n=-1.

'pow2?' ( u -- f  ) gforth-1.0 "pow-two-query"
   f is true iff u is a power of two, i.e., there is exactly one bit set
in u.

'ctz' ( x -- u  ) gforth-1.0 "c-t-z"
   count trailing zeros in binary representation of x

   Unlike most other operations, rotation of narrower units cannot
easily be synthesized from rotation of wider units, so using cell-wide
and double-wide rotation operations means that the results depend on the
cell width.  For published algorithms or cell-width-independent results,
you usually need to use a fixed-width rotation operation.

'wrol' ( u1 u -- u2 ) gforth-1.0 "wrol"
   Rotate the least significant 16 bits of u1 left by u bits, set the
other bits to 0.

'wror' ( u1 u -- u2 ) gforth-1.0 "wror"
   Rotate the least significant 16 bits of u1 right by u bits, set the
other bits to 0.

'lrol' ( u1 u -- u2 ) gforth-1.0 "lrol"
   Rotate the least significant 32 bits of u1 left by u bits, set the
other bits to 0.

'lror' ( u1 u -- u2 ) gforth-1.0 "lror"
   Rotate the least significant 32 bits of u1 right by u bits, set the
other bits to 0.

'rol' ( u1 u -- u2 ) gforth-1.0 "rol"
   Rotate all bits of u1 left by u bits.

'ror' ( u1 u -- u2 ) gforth-1.0 "ror"
   Rotate all bits of u1 right by u bits.

'drol' ( ud1 u -- ud2 ) gforth-1.0 "drol"
   Rotate all bits of ud1 (double-cell) left by u bits.

'dror' ( ud1 u -- ud2 ) gforth-1.0 "dror"
   Rotate all bits of ud1 (double-cell) right by u bits.

6.5.7 Numeric comparison
------------------------

Note that the words that compare for equality ('= <> 0= 0<> d= d<> d0=
d0<>') work for for both signed and unsigned numbers.

'<' ( n1 n2 -- f ) core "less-than"

'<=' ( n1 n2 -- f ) gforth-0.2 "less-or-equal"

'<>' ( n1 n2 -- f ) core-ext "not-equals"

'=' ( n1 n2 -- f ) core "equals"

'>' ( n1 n2 -- f ) core "greater-than"

'>=' ( n1 n2 -- f ) gforth-0.2 "greater-or-equal"

'0<' ( n -- f ) core "zero-less-than"

'0<=' ( n -- f ) gforth-0.2 "zero-less-or-equal"

'0<>' ( n -- f ) core-ext "zero-not-equals"

'0=' ( n -- f ) core "zero-equals"

'0>' ( n -- f ) core-ext "zero-greater-than"

'0>=' ( n -- f ) gforth-0.2 "zero-greater-or-equal"

'u<' ( u1 u2 -- f ) core "u-less-than"

'u<=' ( u1 u2 -- f ) gforth-0.2 "u-less-or-equal"

'u>' ( u1 u2 -- f ) core-ext "u-greater-than"

'u>=' ( u1 u2 -- f ) gforth-0.2 "u-greater-or-equal"

'within' ( u1 u2 u3 -- f ) core-ext "within"
   u2<u3 and u1 in [u2,u3) or: u2>=u3 and u1 not in [u3,u2).  This works
for unsigned and signed numbers (but not a mixture).  Another way to
think about this word is to consider the numbers as a circle (wrapping
around from 'max-u' to 0 for unsigned, and from 'max-n' to min-n for
signed numbers); now consider the range from u2 towards increasing
numbers up to and excluding u3 (giving an empty range if u2=u3); if u1
is in this range, 'within' returns true.

'd<' ( d1 d2 -- f ) double "d-less-than"

'd<=' ( d1 d2 -- f ) gforth-0.2 "d-less-or-equal"

'd<>' ( d1 d2 -- f ) gforth-0.2 "d-not-equals"

'd=' ( d1 d2 -- f ) double "d-equals"

'd>' ( d1 d2 -- f ) gforth-0.2 "d-greater-than"

'd>=' ( d1 d2 -- f ) gforth-0.2 "d-greater-or-equal"

'd0<' ( d -- f ) double "d-zero-less-than"

'd0<=' ( d -- f ) gforth-0.2 "d-zero-less-or-equal"

'd0<>' ( d -- f ) gforth-0.2 "d-zero-not-equals"

'd0=' ( d -- f ) double "d-zero-equals"

'd0>' ( d -- f ) gforth-0.2 "d-zero-greater-than"

'd0>=' ( d -- f ) gforth-0.2 "d-zero-greater-or-equal"

'du<' ( ud1 ud2 -- f ) double-ext "d-u-less-than"

'du<=' ( ud1 ud2 -- f ) gforth-0.2 "d-u-less-or-equal"

'du>' ( ud1 ud2 -- f ) gforth-0.2 "d-u-greater-than"

'du>=' ( ud1 ud2 -- f ) gforth-0.2 "d-u-greater-or-equal"

6.5.8 Floating Point
--------------------

For the rules used by the text interpreter for recognising
floating-point numbers see *note Number Conversion::.

   Gforth has a separate floating point stack, but the documentation
uses the unified notation.(1)

   Floating point numbers have a number of unpleasant surprises for the
unwary (e.g., floating point addition is not associative) and even a few
for the wary.  You should not use them unless you know what you are
doing or you don't care that the results you get are totally bogus.  If
you want to learn about the problems of floating point numbers (and how
to avoid them), you might start with 'David Goldberg, What Every
Computer Scientist Should Know About Floating-Point Arithmetic
(https://docs.oracle.com/cd/E19957-01/806-3568/ncg_goldberg.html), ACM
Computing Surveys 23(1):5-48, March 1991'.

   Conversion between integers and floating-point:

's>f' ( n -- r ) floating-ext "s-to-f"

'd>f' ( d -- r ) floating "d-to-f"

'f>s' ( r -- n ) floating-ext "f-to-s"

'f>d' ( r -- d ) floating "f-to-d"

   Arithmetics:

'f+' ( r1 r2 -- r3 ) floating "f-plus"

'f-' ( r1 r2 -- r3 ) floating "f-minus"

'f*' ( r1 r2 -- r3 ) floating "f-star"

'f/' ( r1 r2 -- r3 ) floating "f-slash"

'fnegate' ( r1 -- r2 ) floating "f-negate"

'fabs' ( r1 -- r2 ) floating-ext "f-abs"

'fcopysign' ( r1 r2 -- r3  ) gforth-1.0 "fcopysign"
   r3 takes its absolute value from r1 and its sign from r2

'fmax' ( r1 r2 -- r3 ) floating "f-max"

'fmin' ( r1 r2 -- r3 ) floating "f-min"

'floor' ( r1 -- r2 ) floating "floor"
   Round towards the next smaller integral value, i.e., round toward
negative infinity.

'fround' ( r1 -- r2 ) floating "f-round"
   Round to the nearest integral value.

'ftrunc' ( r1 -- r2  ) floating-ext "f-trunc"
   round towards 0

'f**' ( r1 r2 -- r3 ) floating-ext "f-star-star"
   r3 is r1 raised to the r2th power.

'fsqrt' ( r1 -- r2 ) floating-ext "f-square-root"

'fexp' ( r1 -- r2 ) floating-ext "f-e-x-p"

'fexpm1' ( r1 -- r2 ) floating-ext "f-e-x-p-m-one"
   r2=e**r1-1

'fln' ( r1 -- r2 ) floating-ext "f-l-n"

'flnp1' ( r1 -- r2 ) floating-ext "f-l-n-p-one"
   r2=ln(r1+1)

'flog' ( r1 -- r2 ) floating-ext "f-log"
   The decimal logarithm.

'falog' ( r1 -- r2 ) floating-ext "f-a-log"
   r2=10**r1

'f2*' ( r1 -- r2  ) gforth-0.2 "f2*"
   Multiply r1 by 2.0e0

'f2/' ( r1 -- r2  ) gforth-0.2 "f2/"
   Multiply r1 by 0.5e0

'1/f' ( r1 -- r2  ) gforth-0.2 "1/f"
   Divide 1.0e0 by r1.

   Vector arithmetics:

'v*' ( f-addr1 nstride1 f-addr2 nstride2 ucount -- r ) gforth-0.5 "v-star"
   dot-product: r=v1*v2.  The first element of v1 is at f_addr1, the
next at f_addr1+nstride1 and so on (similar for v2).  Both vectors have
ucount elements.

'faxpy' ( ra f-x nstridex f-y nstridey ucount -- ) gforth-0.5 "faxpy"
   vy=ra*vx+vy

   Angles in floating point operations are given in radians (a full
circle has 2 pi radians).

'fsin' ( r1 -- r2 ) floating-ext "f-sine"

'fcos' ( r1 -- r2 ) floating-ext "f-cos"

'fsincos' ( r1 -- r2 r3 ) floating-ext "f-sine-cos"
   r2=sin(r1), r3=cos(r1)

'ftan' ( r1 -- r2 ) floating-ext "f-tan"

'fasin' ( r1 -- r2 ) floating-ext "f-a-sine"

'facos' ( r1 -- r2 ) floating-ext "f-a-cos"

'fatan' ( r1 -- r2 ) floating-ext "f-a-tan"

'fatan2' ( r1 r2 -- r3 ) floating-ext "f-a-tan-two"
   r1/r2=tan(r3).  ANS Forth does not require, but probably intends this
to be the inverse of 'fsincos'.  In gforth it is.

'fsinh' ( r1 -- r2 ) floating-ext "f-cinch"

'fcosh' ( r1 -- r2 ) floating-ext "f-cosh"

'ftanh' ( r1 -- r2 ) floating-ext "f-tan-h"

'fasinh' ( r1 -- r2 ) floating-ext "f-a-cinch"

'facosh' ( r1 -- r2 ) floating-ext "f-a-cosh"

'fatanh' ( r1 -- r2 ) floating-ext "f-a-tan-h"

'pi' ( -- r  ) gforth-0.2 "pi"
   'Fconstant' -- r is the value pi; the ratio of a circle's area to its
diameter.

   One particular problem with floating-point arithmetic is that
comparison for equality often fails when you would expect it to succeed.
For this reason approximate equality is often preferred (but you still
have to know what you are doing).  Also note that IEEE NaNs may compare
differently from what you might expect.  The comparison words are:

'f~rel' ( r1 r2 r3 -- flag  ) gforth-0.5 "f~rel"
   Approximate equality with relative error: |r1-r2|<r3*|r1+r2|.

'f~abs' ( r1 r2 r3 -- flag  ) gforth-0.5 "f~abs"
   Approximate equality with absolute error: |r1-r2|<r3.

'f~' ( r1 r2 r3 -- flag  ) floating-ext "f-proximate"
   ANS Forth medley for comparing r1 and r2 for equality: r3>0: 'f~abs';
r3=0: bitwise comparison; r3<0: 'fnegate f~rel'.

'f=' ( r1 r2 -- f ) gforth-0.2 "f-equals"

'f<>' ( r1 r2 -- f ) gforth-0.2 "f-not-equals"

'f<' ( r1 r2 -- f ) floating "f-less-than"

'f<=' ( r1 r2 -- f ) gforth-0.2 "f-less-or-equal"

'f>' ( r1 r2 -- f ) gforth-0.2 "f-greater-than"

'f>=' ( r1 r2 -- f ) gforth-0.2 "f-greater-or-equal"

'f0<' ( r -- f ) floating "f-zero-less-than"

'f0<=' ( r -- f ) gforth-0.2 "f-zero-less-or-equal"

'f0<>' ( r -- f ) gforth-0.2 "f-zero-not-equals"

'f0=' ( r -- f ) floating "f-zero-equals"

'f0>' ( r -- f ) gforth-0.2 "f-zero-greater-than"

'f0>=' ( r -- f ) gforth-0.2 "f-zero-greater-or-equal"

   Special values in IEEE754 can be derived by for example dividing by
zero.  The most common ones are defined as floating point constants for
easy usage.

'infinity' ( -- r  ) gforth-1.0 "infinity"
   floating point infinity

'-infinity' ( -- r  ) gforth-1.0 "-infinity"
   floating point -infinity

'NaN' ( -- r  ) gforth-1.0 "NaN"
   floating point Not a Number

   ---------- Footnotes ----------

   (1) It's easy to generate the separate notation from that by just
separating the floating-point numbers out: e.g.  '( n r1 u r2 -- r3 )'
becomes '( n u -- ) ( F: r1 r2 -- r3 )'.

6.6 Stack Manipulation
======================

Gforth maintains a number of separate stacks:

   * A data stack (also known as the "parameter stack") -- for
     characters, cells, addresses, and double cells.

   * A floating point stack -- for holding floating point (FP) numbers.

   * A return stack -- for holding the return addresses of colon
     definitions and other (non-FP) data.

   * A locals stack -- for holding local variables.

6.6.1 Data stack
----------------

'drop' ( w -- ) core "drop"

'nip' ( w1 w2 -- w2 ) core-ext "nip"

'dup' ( w -- w w ) core "dupe"

'over' ( w1 w2 -- w1 w2 w1 ) core "over"

'third' ( w1 w2 w3 -- w1 w2 w3 w1 ) gforth-1.0 "third"

'fourth' ( w1 w2 w3 w4 -- w1 w2 w3 w4 w1 ) gforth-1.0 "fourth"

'tuck' ( w1 w2 -- w2 w1 w2 ) core-ext "tuck"

'swap' ( w1 w2 -- w2 w1 ) core "swap"

'pick' ( S:... u -- S:... w ) core-ext "pick"
   Actually the stack effect is ' x0 ... xu u -- x0 ... xu x0 '.

'rot' ( w1 w2 w3 -- w2 w3 w1 ) core "rote"

'-rot' ( w1 w2 w3 -- w3 w1 w2 ) gforth-0.2 "not-rote"

'?dup' ( w -- S:... w ) core "question-dupe"
   Actually the stack effect is: '( w -- 0 | w w )'.  It performs a
'dup' if w is nonzero.

'roll' ( x0 x1 .. xn n -- x1 .. xn x0  ) core-ext "roll"

'2drop' ( w1 w2 -- ) core "two-drop"

'2nip' ( w1 w2 w3 w4 -- w3 w4 ) gforth-0.2 "two-nip"

'2dup' ( w1 w2 -- w1 w2 w1 w2 ) core "two-dupe"

'2over' ( w1 w2 w3 w4 -- w1 w2 w3 w4 w1 w2 ) core "two-over"

'2tuck' ( w1 w2 w3 w4 -- w3 w4 w1 w2 w3 w4 ) gforth-0.2 "two-tuck"

'2swap' ( w1 w2 w3 w4 -- w3 w4 w1 w2 ) core "two-swap"

'2rot' ( w1 w2 w3 w4 w5 w6 -- w3 w4 w5 w6 w1 w2 ) double-ext "two-rote"

6.6.2 Floating point stack
--------------------------

'fdrop' ( r -- ) floating "f-drop"

'fnip' ( r1 r2 -- r2 ) gforth-0.2 "f-nip"

'fdup' ( r -- r r ) floating "f-dupe"

'fover' ( r1 r2 -- r1 r2 r1 ) floating "f-over"

'fthird' ( r1 r2 r3 -- r1 r2 r3 r1 ) gforth-1.0 "fthird"

'ffourth' ( r1 r2 r3 r4 -- r1 r2 r3 r4 r1 ) gforth-1.0 "ffourth"

'ftuck' ( r1 r2 -- r2 r1 r2 ) gforth-0.2 "f-tuck"

'fswap' ( r1 r2 -- r2 r1 ) floating "f-swap"

'fpick' ( f:... u -- f:... r ) gforth-0.4 "fpick"
   Actually the stack effect is ' r0 ... ru u -- r0 ... ru r0 '.

'frot' ( r1 r2 r3 -- r2 r3 r1 ) floating "f-rote"

'f-rot' ( r1 r2 r3 -- r3 r1 r2 ) floating "f-not-rote"

6.6.3 Return stack
------------------

A Forth system is allowed to keep local variables on the return stack.
This is reasonable, as local variables usually eliminate the need to use
the return stack explicitly.  So, if you want to produce a standard
compliant program and you are using local variables in a word, forget
about return stack manipulations in that word (refer to the standard
document for the exact rules).

'>r' ( w -- R:w ) core "to-r"

'r>' ( R:w -- w ) core "r-from"

'r@' ( -- w ; R: w -- w  ) core "r-fetch"

'rdrop' ( R:w -- ) gforth-0.2 "rdrop"

'2>r' ( w1 w2 -- R:w1 R:w2 ) core-ext "two-to-r"

'2r>' ( R:w1 R:w2 -- w1 w2 ) core-ext "two-r-from"

'2r@' ( R:w1 R:w2 -- R:w1 R:w2 w1 w2 ) core-ext "two-r-fetch"

'2rdrop' ( R:w1 R:w2 -- ) gforth-0.2 "two-r-drop"

'n>r' ( x1 .. xn n -- r:xn..x1 r:n  ) tools-ext "n-to-r"

'nr>' ( r:xn..x1 r:n -- x1 .. xn n  ) tools-ext "n-r-from"

6.6.4 Locals stack
------------------

Gforth uses an extra locals stack.  It is described, along with the
reasons for its existence, in *note Locals implementation::.

6.6.5 Stack pointer manipulation
--------------------------------

'sp0' ( -- a-addr  ) gforth-0.4 "sp0"
   'User' variable -- initial value of the data stack pointer.

'sp@' ( S:... -- a-addr ) gforth-0.2 "sp-fetch"

'sp!' ( a-addr -- S:... ) gforth-0.2 "sp-store"

'fp0' ( -- a-addr  ) gforth-0.4 "fp0"
   'User' variable -- initial value of the floating-point stack pointer.

'fp@' ( f:... -- f-addr ) gforth-0.2 "fp-fetch"

'fp!' ( f-addr -- f:... ) gforth-0.2 "fp-store"

'rp0' ( -- a-addr  ) gforth-0.4 "rp0"
   'User' variable -- initial value of the return stack pointer.

'rp@' ( -- a-addr ) gforth-0.2 "rp-fetch"

'rp!' ( a-addr -- ) gforth-0.2 "rp-store"

'lp0' ( -- a-addr  ) gforth-0.4 "lp0"
   'User' variable -- initial value of the locals stack pointer.

'lp@' ( -- c-addr ) gforth-0.2 "lp-fetch"
   C_addr is the current value of the locals stack pointer.

'lp!' ( c-addr -- ) gforth-internal "lp-store"

6.7 Memory
==========

In addition to the standard Forth memory allocation words, there is also
a garbage collector
(https://www.complang.tuwien.ac.at/forth/garbage-collection.zip).

6.7.1 Memory model
------------------

Standard Forth considers a Forth system as consisting of several address
spaces, of which only "data space" is managed and accessible with the
memory words.  Memory not necessarily in data space includes the stacks,
the code (called code space) and the headers (called name space).  In
Gforth everything is in data space, but the code for the primitives is
usually read-only.

   Data space is divided into a number of areas: The (data space portion
of the) dictionary(1), the heap, and a number of system-allocated
buffers.

   Gforth provides one big address space, and address arithmetic can be
performed between any addresses.  However, in the dictionary headers or
code are interleaved with data, so almost the only contiguous data space
regions there are those described by Standard Forth as contiguous; but
you can be sure that the dictionary is allocated towards increasing
addresses even between contiguous regions.  The memory order of
allocations in the heap is platform-dependent (and possibly different
from one run to the next).

   ---------- Footnotes ----------

   (1) Sometimes, the term "dictionary" is used to refer to the search
data structure embodied in word lists and headers, because it is used
for looking up names, just as you would in a conventional dictionary.

6.7.2 Dictionary allocation
---------------------------

Dictionary allocation is a stack-oriented allocation scheme, i.e., if
you want to deallocate X, you also deallocate everything allocated after
X.

   The allocations using the words below are contiguous and grow the
region towards increasing addresses.  Other words that allocate
dictionary memory of any kind (i.e., defining words including ':noname')
end the contiguous region and start a new one.

   In Standard Forth only 'create'd words are guaranteed to produce an
address that is the start of the following contiguous region.  In
particular, the cell allocated by 'variable' is not guaranteed to be
contiguous with following 'allot'ed memory.

   You can deallocate memory by using 'allot' with a negative argument
(with some restrictions, see 'allot').  For larger deallocations use
'marker'.

'here' ( -- addr  ) core "here"
   Return the address of the next free location in data space.

'unused' ( -- u  ) core-ext "unused"
   Return the amount of free space remaining (in address units) in the
region addressed by 'here'.

'allot' ( n --  ) core "allot"
   Reserve n address units of data space without initialization.  n is a
signed number, passing a negative n releases memory.  In ANS Forth you
can only deallocate memory from the current contiguous region in this
way.  In Gforth you can deallocate anything in this way but named words.
The system does not check this restriction.

'->here' ( addr --  ) gforth-1.0 "to-here"
   Change the value of 'here' to addr.

'c,' ( c --  ) core "c-comma"
   Reserve data space for one char and store c in the space.

'f,' ( f --  ) gforth-0.2 "f,"
   Reserve data space for one floating-point number and store f in the
space.

',' ( w --  ) core "comma"
   Reserve data space for one cell and store w in the space.

'2,' ( w1 w2 --  ) gforth-0.2 "2,"
   Reserve data space for two cells and store the double w1 w2 there, w2
first (lower address).

'w,' ( w --  ) gforth-1.0 "w-comma"

'l,' ( l --  ) gforth-1.0 "l-comma"

'x,' ( x --  ) gforth-1.0 "x-comma"

'xd,' ( xd --  ) gforth-1.0 "x-d-comma"

'A,' ( addr --  ) gforth-0.2 "A,"
   Reserve data space for one cell, and store addr there.  For our
cross-compiler this provides the type information necessary for a
relocatable image; normally, though, this is equivalent to ','.

'mem,' ( addr u --  ) gforth-0.6 "mem,"

   doc-save-mem-dict

   Memory accesses have to be aligned (*note Address arithmetic::).  So
of course you should allocate memory in an aligned way, too.  I.e.,
before allocating allocating a cell, 'here' must be cell-aligned, etc.
The words below align 'here' if it is not already.  Basically it is only
already aligned for a type, if the last allocation was a multiple of the
size of this type and if 'here' was aligned for this type before.

   After freshly 'create'ing a word, 'here' is 'align'ed in Standard
Forth ('maxalign'ed in Gforth).

'align' ( --  ) core "align"
   If the data-space pointer is not aligned, reserve enough space to
align it.

'falign' ( --  ) floating "f-align"
   If the data-space pointer is not float-aligned, reserve enough space
to align it.

'sfalign' ( --  ) floating-ext "s-f-align"
   If the data-space pointer is not single-float-aligned, reserve enough
space to align it.

'dfalign' ( --  ) floating-ext "d-f-align"
   If the data-space pointer is not double-float-aligned, reserve enough
space to align it.

'maxalign' ( --  ) gforth-0.2 "maxalign"
   Align data-space pointer for all alignment requirements.

'cfalign' ( --  ) gforth-0.2 "cfalign"
   Align data-space pointer for code field requirements (i.e., such that
the corresponding body is maxaligned).

6.7.3 Heap allocation
---------------------

Heap allocation supports deallocation of allocated memory in any order.
Dictionary allocation is not affected by it (i.e., it does not end a
contiguous region).  In Gforth, these words are implemented using the
standard C library calls malloc(), free() and realloc().

   The memory region produced by one invocation of 'allocate' or
'resize' is internally contiguous.  There is no contiguity between such
a region and any other region (including others allocated from the
heap).

'allocate' ( u -- a_addr wior  ) memory "allocate"
   Allocate u address units of contiguous data space.  The initial
contents of the data space is undefined.  If the allocation is
successful, a-addr is the start address of the allocated region and wior
is 0.  If the allocation fails, a-addr is undefined and wior is a
non-zero I/O result code.

'free' ( a_addr -- wior  ) memory "free"
   Return the region of data space starting at a-addr to the system.
The region must originally have been obtained using 'allocate' or
'resize'.  If the operational is successful, wior is 0.  If the
operation fails, wior is a non-zero I/O result code.

'resize' ( a_addr1 u -- a_addr2 wior  ) memory "resize"
   Change the size of the allocated area at a-addr1 to u address units,
possibly moving the contents to a different area.  a-addr2 is the
address of the resulting area.  If the operation is successful, wior is
0.  If the operation fails, wior is a non-zero I/O result code.  If
a-addr1 is 0, Gforth's (but not the Standard) 'resize' 'allocate's u
address units.

   The following words are useful for dealing with memory blocks:

'save-mem' ( addr1 u -- addr2 u  ) gforth-0.2 "save-mem"
   Copy a memory block into a newly allocated region in the heap.

'free-mem-var' ( addr --  ) gforth-experimental "free-mem-var"
   Addr is the address of a 2variable containing address and size of a
memory range; frees memory and clears the 2variable.

'extend-mem' ( addr1 u1 u -- addr addr2 u2  ) gforth-experimental "extend-mem"
   Extend memory block addr1 u1 allocated from the heap by u aus.  The
(possibly reallocated) piece is addr2 u2, the extension is at addr.

   The $tring words can also be used for dealing with memory blocks,
*Note $tring words::.

   For growable memory buffers you can use $trings, or the following
words.  Because the allocated memory of a buffer managed with
'adjust-buffer' does not shrink, there is no heap-management overhead
when adjusting the buffer for a size smaller than the largest one seen
yet.

'buffer%' ( u1 u2 --  ) gforth-experimental "buffer%"
   u1 is the alignment and u2 is the size of a buffer descriptor.

'init-buffer' ( addr --  ) gforth-experimental "init-buffer"

'adjust-buffer' ( u addr --  ) gforth-experimental "adjust-buffer"
   Adjust buffer% at addr to length u.  This may grow the allocated
area, but never shrinks it.

   You can get the current address and length of such a buffer with
'2@'.

   Typical usage:

     create mybuf  buffer% %size allot  mybuf init-buffer
     s" frobnicate" mybuf adjust-buffer  mybuf 2@ move
     mybuf 2@ type
     s" foo"        mybuf adjust-buffer  mybuf 2@ move
     mybuf 2@ type

6.7.4 Memory Access
-------------------

'@' ( a-addr -- w ) core "fetch"
   w is the cell stored at a_addr.

'!' ( w a-addr -- ) core "store"
   Store w into the cell at a-addr.

'+!' ( n a-addr -- ) core "plus-store"
   Add n to the cell at a-addr.

'c@' ( c-addr -- c ) core "c-fetch"
   c is the char stored at c_addr.

'c!' ( c c-addr -- ) core "c-store"
   Store c into the char at c-addr.

'2@' ( a-addr -- w1 w2 ) core "two-fetch"
   w2 is the content of the cell stored at a-addr, w1 is the content of
the next cell.

'2!' ( w1 w2 a-addr -- ) core "two-store"
   Store w2 into the cell at c-addr and w1 into the next cell.

'f@' ( f-addr -- r ) floating "f-fetch"
   r is the float at address f-addr.

'f!' ( r f-addr -- ) floating "f-store"
   Store r into the float at address f-addr.

'sf@' ( sf-addr -- r ) floating-ext "s-f-fetch"
   Fetch the single-precision IEEE floating-point value r from the
address sf-addr.

'sf!' ( r sf-addr -- ) floating-ext "s-f-store"
   Store r as single-precision IEEE floating-point value to the address
sf-addr.

'df@' ( df-addr -- r ) floating-ext "d-f-fetch"
   Fetch the double-precision IEEE floating-point value r from the
address df-addr.

'df!' ( r df-addr -- ) floating-ext "d-f-store"
   Store r as double-precision IEEE floating-point value to the address
df-addr.

6.7.5 Special Memory Accesses
-----------------------------

This section is about memory accesses useful for communicating with
other software or other computers.  This means that the accesses are of
a certain bit width (independent of Gforth's cell width), are possibly
not naturally aligned and typically have a certain byte order that may
be different from the native byte order of the system that Gforth runs
on.

   We use the following prefixes:

'c'
     8 bits (character)
'w'
     16 bits
'l'
     32 bits
'x'
     64 bits represented as one cell
'xd'
     64 bits represented as two cells

   The 'x'-prefix words do not work properly on 32-bit systems, so for
code that is intended to be portable to 32-bit systems you should use
'xd'-prefix words.  Note that 'xd'-prefix words work on 64-bit systems:
there the upper cell is just 0 (for unsigned values) or a sign extension
of the lower cell.

   The memory-access words below all work with arbitrarily (un)aligned
addresses (unlike '@', '!', 'f@', 'f!', which require alignment on some
hardware).

'w@' ( c-addr -- u ) gforth-0.5 "w-fetch"
   u is the zero-extended 16-bit value stored at c_addr.

'w!' ( w c-addr -- ) gforth-0.7 "w-store"
   Store the bottom 16 bits of w at c_addr.

'l@' ( c-addr -- u ) gforth-0.7 "l-fetch"
   u is the zero-extended 32-bit value stored at c_addr.

'l!' ( w c-addr -- ) gforth-0.7 "l-store"
   Store the bottom 32 bits of w at c_addr.

'x@' ( c-addr -- u ) gforth-1.0 "x-fetch"
   u is the zero-extended 64-bit value stored at c_addr.

'x!' ( w c-addr -- ) gforth-1.0 "x-store"
   Store the bottom 64 bits of w at c_addr.

'xd@' ( c-addr -- ud ) gforth-1.0 "x-d-fetch"
   ud is the zero-extended 64-bit value stored at c_addr.

'xd!' ( ud c-addr -- ) gforth-1.0 "x-d-store"
   Store the bottom 64 bits of ud at c_addr.

   For accesses with a specific byte order, you have to perform
byte-order adjustment immediately after a fetch (before the
sign-extension), or immediately before the store.  The results of these
byte-order adjustment words are always zero-extended.

'wbe' ( u1 -- u2  ) gforth-1.0 "wbe"
   Convert 16-bit value in u1 from native byte order to big-endian or
from big-endian to native byte order (the same operation)

'wle' ( u1 -- u2  ) gforth-1.0 "wle"
   Convert 16-bit value in u1 from native byte order to little-endian or
from little-endian to native byte order (the same operation)

'lbe' ( u1 -- u2  ) gforth-1.0 "lbe"
   Convert 32-bit value in u1 from native byte order to big-endian or
from big-endian to native byte order (the same operation)

'lle' ( u1 -- u2  ) gforth-1.0 "lle"
   Convert 32-bit value in u1 from native byte order to little-endian or
from little-endian to native byte order (the same operation)

'xbe' ( u1 -- u2  ) gforth-1.0 "xbe"
   Convert 64-bit value in u1 from native byte order to big-endian or
from big-endian to native byte order (the same operation)

'xle' ( u1 -- u2  ) gforth-1.0 "xle"
   Convert 64-bit value in u1 from native byte order to little-endian or
from little-endian to native byte order (the same operation)

'xdbe' ( ud1 -- ud2  ) gforth-1.0 "xdbe"
   Convert 64-bit value in ud1 from native byte order to big-endian or
from big-endian to native byte order (the same operation)

'xdle' ( ud1 -- ud2  ) gforth-1.0 "xdle"
   Convert 64-bit value in ud1 from native byte order to little-endian
or from little-endian to native byte order (the same operation)

   For signed fetches with a specific byte order, you have to perform a
sign-extension word after an unsigned fetch and a byte-order correction:

'c>s' ( x -- n ) gforth-1.0 "c-to-s"
   Sign-extend the 8-bit value in x to cell n.

'w>s' ( x -- n ) gforth-1.0 "w-to-s"
   Sign-extend the 16-bit value in x to cell n.

'l>s' ( x -- n ) gforth-1.0 "l-to-s"
   Sign-extend the 32-bit value in x to cell n.

'x>s' ( x -- n  ) gforth-1.0 "x>s"
   Sign-extend the 64-bit value in x to cell n.

'xd>s' ( xd -- d  ) gforth-1.0 "xd>s"
   Sign-extend the 64-bit value in XD to double-ceel D.

   Overall, this leads to sequences like

     w@ wbe w>s   \ 16-bit unaligned signed big-endian fetch
     >r lle r> l! \ 32-bit unaligned little-endian store

6.7.6 Address arithmetic
------------------------

Address arithmetic is the foundation on which you can build data
structures like arrays, records (*note Structures::) and objects (*note
Object-oriented Forth::).

   Standard Forth does not specify the sizes of the data types.
Instead, it offers a number of words for computing sizes and doing
address arithmetic.  Address arithmetic is performed in terms of address
units (aus); on most systems the address unit is one byte.  Note that a
character may have more than one au, so 'chars' is no noop (on platforms
where it is a noop, it compiles to nothing).

   The basic address arithmetic words are '+' and '-'.  E.g., if you
have the address of a cell, perform '1 cells +', and you will have the
address of the next cell.

   Standard Forth also defines words for aligning addresses for specific
types.  Many computers require that accesses to specific data types must
only occur at specific addresses; e.g., that cells may only be accessed
at addresses divisible by 4.  Even if a machine allows unaligned
accesses, it can usually perform aligned accesses faster.

   For the performance-conscious: alignment operations are usually only
necessary during the definition of a data structure, not during the
(more frequent) accesses to it.

   Standard Forth defines no words for character-aligning addresses; in
Forth-2012 all addresses are character-aligned.

   Standard Forth guarantees that addresses returned by 'CREATE'd words
are cell-aligned; in addition, Gforth guarantees that these addresses
are aligned for all purposes.

   Note that the Standard Forth word 'char' has nothing to do with
address arithmetic.

'chars' ( n1 -- n2  ) core "chars"
   n2 is the number of address units of n1 chars.""

'char+' ( c-addr1 -- c-addr2 ) core "char-plus"
   '1 chars +'.

'char-' ( c-addr1 -- c-addr2  ) gforth-0.7 "char-minus"

'cells' ( n1 -- n2 ) core "cells"
   n2 is the number of address units of n1 cells.

'cell+' ( a-addr1 -- a-addr2 ) core "cell-plus"
   '1 cells +'

'cell-' ( a-addr1 -- a-addr2 ) core "cell-minus"
   '1 cells -'

'cell/' ( n1 -- n2 ) gforth-1.0 "cell-divide"
   n2 is the number of cells that fit into n1

'cell' ( -- u  ) gforth-0.2 "cell"
   'Constant' -- '1 cells'

'aligned' ( c-addr -- a-addr ) core "aligned"
   a-addr is the first aligned address greater than or equal to c-addr.

'floats' ( n1 -- n2 ) floating "floats"
   n2 is the number of address units of n1 floats.

'float+' ( f-addr1 -- f-addr2 ) floating "float-plus"
   '1 floats +'.

'float' ( -- u  ) gforth-0.3 "float"
   'Constant' -- the number of address units corresponding to a
floating-point number.

'float/' ( n1 -- n2 ) gforth-1.0 "float-divide"

'faligned' ( c-addr -- f-addr ) floating "f-aligned"
   f-addr is the first float-aligned address greater than or equal to
c-addr.

'sfloats' ( n1 -- n2 ) floating-ext "s-floats"
   n2 is the number of address units of n1 single-precision IEEE
floating-point numbers.

'sfloat+' ( sf-addr1 -- sf-addr2  ) floating-ext "s-float-plus"
   '1 sfloats +'.

'sfloat/' ( n1 -- n2 ) gforth-1.0 "dfloat-divide"

'sfaligned' ( c-addr -- sf-addr ) floating-ext "s-f-aligned"
   sf-addr is the first single-float-aligned address greater than or
equal to c-addr.

'dfloats' ( n1 -- n2 ) floating-ext "d-floats"
   n2 is the number of address units of n1 double-precision IEEE
floating-point numbers.

'dfloat+' ( df-addr1 -- df-addr2  ) floating-ext "d-float-plus"
   '1 dfloats +'.

'dfloat/' ( n1 -- n2 ) gforth-1.0 "sfloat-divide"

'dfaligned' ( c-addr -- df-addr ) floating-ext "d-f-aligned"
   df-addr is the first double-float-aligned address greater than or
equal to c-addr.

'maxaligned' ( addr1 -- addr2  ) gforth-0.2 "maxaligned"
   addr2 is the first address after addr1 that satisfies all alignment
restrictions.  maxaligned"

'cfaligned' ( addr1 -- addr2  ) gforth-0.2 "cfaligned"
   addr2 is the first address after addr1 that is aligned for a code
field (i.e., such that the corresponding body is maxaligned).

'*aligned' ( addr1 n -- addr2  ) gforth-1.0 "*aligned"
   ADDR2 is the aligned version of ADDR1 with respect to the alignment
N.

'*align' ( n --  ) gforth-1.0 "*align"
   Align 'here' with respect to the alignment N.

'waligned' ( addr -- addr'  ) gforth-1.0 "waligned"
   Addr' is the next even address >= addr.

'walign' ( --  ) gforth-1.0 "walign"
   Align 'here' to even.

'laligned' ( addr -- addr'  ) gforth-1.0 "laligned"
   Addr' is the next address >= addr divisible by 4.

'lalign' ( --  ) gforth-1.0 "lalign"
   Align 'here' to be divisible by 4.

'xaligned' ( addr -- addr'  ) gforth-1.0 "xaligned"
   Addr' is the next address >= addr divisible by 8.

'xalign' ( --  ) gforth-1.0 "xalign"
   Align 'here' to be divisible by 8.

   The environmental query 'address-unit-bits' (*note Environmental
Queries::) and the following words may be useful to those who want to
write software portable to non-byte-addressed machines.

'/w' ( -- u  ) gforth-0.7 "slash-w"
   address units for a 16-bit value

'/l' ( -- u  ) gforth-0.7 "slash-l"
   address units for a 32-bit value

'/x' ( -- u  ) gforth-1.0 "slash-x"
   address units for a 64-bit value

6.7.7 Memory Blocks
-------------------

Memory blocks often represent character strings; For ways of storing
character strings in memory see *note String representations::.  For
other string-processing words see *note Displaying characters and
strings::.

   A few of these words work on address unit blocks.  In that case, you
usually have to insert 'CHARS' before the word when working on character
strings.  Most words work on character blocks, and expect a char-aligned
address.

   When copying characters between overlapping memory regions, use
'move'.  'Cmove' and 'cmove>' tend to be slower than a well-implemented
'move'.

'move' ( c-from c-to ucount -- ) core "move"
   Copy the contents of ucount aus at c-from to c-to.  'move' works
correctly even if the two areas overlap.

'cmove' ( c-from c-to u -- ) string "c-move"
   Copy the contents of ucount characters from data space at c-from to
c-to.  The copy proceeds 'char'-by-'char' from low address to high
address; i.e., for overlapping areas it is safe if c-to<=c-from.

'cmove>' ( c-from c-to u -- ) string "c-move-up"
   Copy the contents of ucount characters from data space at c-from to
c-to.  The copy proceeds 'char'-by-'char' from high address to low
address; i.e., for overlapping areas it is safe if c-to>=c-from.

'fill' ( c-addr u c -- ) core "fill"
   Store c in u chars starting at c-addr.

'erase' ( addr u --  ) core-ext "erase"
   Clear all bits in u aus starting at addr.

'blank' ( c-addr u --  ) string "blank"
   Store the space character into u chars starting at c-addr.

'insert' ( string length buffer size --  ) gforth-0.7 "insert"
   inserts a string at the front of a buffer.  The remaining bytes are
moved on.

'delete' ( buffer size u --  ) gforth-0.7 "delete"
   deletes the first U bytes from a buffer and fills the rest at the end
with blanks.

'compare' ( c-addr1 u1 c-addr2 u2 -- n ) string "compare"
   Compare two strings lexicographically, based on the values of the
bytes in the strings (i.e., case-sensitive and without locale-specific
collation order orderings).  If they are equal, n is 0; if the first
string is smaller, n is -1; if the first string is larger, n is 1.

'pad' ( -- c-addr  ) core-ext "pad"
   C-ADDR is the address of a transient region that can be used as
temporary data storage.  At least 84 characters of space is available.

6.8 Strings and Characters
==========================

6.8.1 Characters
----------------

Forth supports chars (aka bytes), used by words such as 'c@'; these can
be used to represent an ASCII character.

   Forth also supports extended characters, which may be represented by
a sequence of several bytes (i.e., several chars).  A common character
encoding is the UTF-8 representation of Unicode.

   In general, most code does not have to worry about extended
characters: In the string representation it does not matter whether a
byte is a part of an extended character, or it is a character by itself,
and words that consume chars (like 'emit') also work when the extended
character is transferred as a sequence of chars.  Forth still provides
words for dealing with extended characters (*note Xchars and Unicode::).

   In Unicode terms, chars are code units, whereas extended characters
are code points.  Note that an Unicode abstract character can consist of
a sequence of code points, but Forth (like other programming languages)
has no data type for individual abstract characters; of course, they can
be represented as strings.

   You can use the usual integer words on chars and Xchars on the stack,
but Gforth also has some words for dealing with chars on the stack:

'toupper' ( c1 -- c2 ) gforth-0.2 "toupper"
   If c1 is a lower-case ASCII character, c2 is the equivalent
upper-case character, otherwise c2 is c1.

6.8.2 String representations
----------------------------

Forth commonly represents strings as cell pair c-addr u on the stack; u
is the length of the string in bytes (aka chars), and c-addr is the
address of the first byte of the string.  Note that a code point may be
represented by a sequence of several chars in the string (and a Unicode
"abstract character" may consist of several code points).  *Note String
words::.

   Another string representation is used with the string library of
words containing '$'.  It represents the string on the stack through the
address of a cell-sized string handle, which can be located in, e.g., a
variable.  *Note $tring words::.

   A legacy string representation are "counted strings", represented on
the stack by c-addr.  The char addressed by c-addr contains a
character-count, n, of the string and the string occupies the subsequent
n char addresses in memory.  Counted strings are limited to 255 bytes in
length.  While counted strings may look attractive due to needing only
one stack item, due to their limitations we recommend avoiding them,
especially as input parameters of words.  *Note Counted string words::.

6.8.3 String and Character literals
-----------------------------------

The nicest way to write a string literal is to write it as '"STRING"'.
You can use the same \-escapes inside as for 's\"'.  However, this way
is non-standard, so you may want to use one of the following words for
improved portability:

's\"' ( compilation 'ccc"' -- ; run-time -- c-addr u  ) core-ext,file-ext "s-backslash-quote"
   Like 'S"', but translates C-like \-escape-sequences, as follows: '\a'
BEL (alert), '\b' BS, '\e' ESC (not in C99), '\f' FF, '\n' newline, '\r'
CR, '\t' HT, '\v' VT, '\"' ", '\\' \, '\'[0-7]{1,3} octal numerical
character value (non-standard), '\x'[0-9a-f]{0,2} hex numerical
character value (standard only with two digits), '\u'[0-9a-f]{4} for
unicode codepoints (auto-merges surrogate pairs), '\U'[0-9a-f]{8} for
extended unicode code points; a '\' before any other character is
reserved.
Note that '\x'XX produces raw bytes, while '\u'XXXX and '\U'XXXXXXXX
produce code points for the current encoding.  E.g., if we use UTF-8
encoding and want to encode ä (code point U+00E4), you can write the
letter ä itself, or write '\xc3\xa4' (the UTF-8 bytes for this code
point), '\u00e4', or '\U000000e4'.
Note that, unlike in C, '\n' produces the preferred newline sequence for
the host OS, which may consist of several chars.  I.e., '"\n"' is
equivalent to 'newline'.

'S"' ( compilation 'ccc"' -- ; run-time -- c-addr u  ) core,file "s-quote"
   Compilation: Parse a string ccc delimited by a '"' (double quote).
At run-time, return the length, u, and the start address, c-addr of the
string.  Interpretation: parse the string as before, and return c-addr,
u.  Gforth 'allocate's the string.  The resulting memory leak is usually
not a problem; the exception is if you create strings containing 'S"'
and 'evaluate' them; then the leak is not bounded by the size of the
interpreted files and you may want to 'free' the strings.  Forth-2012
only guarantees two buffers of 80 characters each, so in standard
programs you should assume that the string lives only until the
next-but-one 's"'.

   Likewise, You can get the code xc of a character C with ''C''.  This
way has been standardized since Forth-2012.  An older way to get it is
to use one of the following words:

'char' ( '<spaces>ccc' -- c  ) core,xchar-ext "char"
   Skip leading spaces.  Parse the string ccc and return c, the display
code representing the first character of ccc.

'[char]' ( compilation '<spaces>ccc' -- ; run-time -- c  ) core,xchar-ext "bracket-char"
   Compilation: skip leading spaces.  Parse the string ccc.  Run-time:
return c, the display code representing the first character of ccc.
Interpretation semantics for this word are undefined.

   You usually use 'char' outside and '[char]' inside colon definitions,
or you just use ''C''.

   Note that, e.g.,

     "C" type

is (slightly) more efficient than

     'C' xemit

because the latter converts the code point into a sequence of bytes and
individually 'emit's them.  Similarly, dealing with general characters
is usually more efficient when representing them as strings rather than
code points.

   There are the following words for producing commonly-used characters
and strings that cannot be produced with 'S"' or ''C'':

'newline' ( -- c-addr u ) gforth-0.5 "newline"
   String containing the newline sequence of the host OS

'bl' ( -- c-char  ) core "b-l"
   c-char is the character value for a space.

'#tab' ( -- c  ) gforth-0.2 "number-tab"

'#lf' ( -- c  ) gforth-0.2 "number-l-f"

'#cr' ( -- c  ) gforth-0.2 "number-c-r"

'#ff' ( -- c  ) gforth-0.2 "number-f-f"

'#bs' ( -- c  ) gforth-0.2 "number-b-s"

'#del' ( -- c  ) gforth-0.2 "number-del"

'#bell' ( -- c  ) gforth-0.2 "number-bell"

'#esc' ( -- c  ) gforth-0.5 "number-esc"

'#eof' ( -- c  ) gforth-0.7 "number-e-o-f"
   actually EOT (ASCII code 4 aka '^D')

6.8.4 String words
------------------

Words that are used for memory blocks are also useful for strings, so
for words that move, copy, compare and search strings, see *note Memory
Blocks::.  For words that display characters and strings, see *note
Displaying characters and strings::.

   The following words work on previously existing strings:

'str=' ( c-addr1 u1 c-addr2 u2 -- f  ) gforth-0.6 "str-equals"

'str<' ( c-addr1 u1 c-addr2 u2 -- f  ) gforth-0.6 "str-less-than"

'string-prefix?' ( c-addr1 u1 c-addr2 u2 -- f  ) gforth-0.6 "string-prefix-question"
   Is C-ADDR2 U2 a prefix of C-ADDR1 U1?

'string-suffix?' ( c-addr1 u1 c-addr2 u2 -- f  ) gforth-1.0 "string-suffix-question"
   Is C-ADDR2 U2 a suffix of C-ADDR1 U1?

'search' ( c-addr1 u1 c-addr2 u2 -- c-addr3 u3 flag  ) string "search"
   Search the string specified by c-addr1, u1 for the string specified
by c-addr2, u2.  If flag is true: match was found at c-addr3 with u3
characters remaining.  If flag is false: no match was found; c-addr3, u3
are equal to c-addr1, u1.

'scan' ( c-addr1 u1 c -- c-addr2 u2 ) gforth-0.2 "scan"
   Skip all characters not equal to c.  The result starts with c or is
empty.  'Scan' is limited to single-byte (ASCII) characters.  Use
'search' to search for multi-byte characters.

'scan-back' ( c-addr u1 c -- c-addr u2  ) gforth-0.7 "scan-back"

'skip' ( c-addr1 u1 c -- c-addr2 u2 ) gforth-0.2 "skip"
   Skip all characters equal to c.  The result starts with the first
non-c character, or it is empty.  'Scan' is limited to single-byte
(ASCII) characters.

'-trailing' ( c_addr u1 -- c_addr u2  ) string "dash-trailing"
   Adjust the string specified by c-addr, u1 to remove all trailing
spaces.  u2 is the length of the modified string.

'/string' ( c-addr1 u1 n -- c-addr2 u2 ) string "slash-string"
   Adjust the string specified by c-addr1, u1 to remove n characters
from the start of the string.

'safe/string' ( c-addr1 u1 n -- c-addr2 u2 ) gforth-1.0 "safe-slash-string"
   Adjust the string specified by c-addr1, u1 to remove n characters
from the start of the string.  Unlike '/string', 'safe/string' removes
at least 0 and at most u1 characters.

'cstring>sstring' ( c-addr -- c-addr u  ) gforth-0.2 "cstring-to-sstring"
   C-addr is the start address of a zero-terminated string, u is its
length.

   The following words compare case-insensitively for ASCII characters,
but case-sensitively for non-ASCII characters (like in lookup in
wordlists).

'capscompare' ( c-addr1 u1 c-addr2 u2 -- n ) gforth-0.7 "capscompare"
   Compare two strings lexicographically, based on the values of the
bytes in the strings, but comparing ASCII characters case-insensitively,
and non-ASCII characters case-sensitively and without locale-specific
collation order.  If they are equal, n is 0; if the first string is
smaller, n is -1; if the first string is larger, n is 1.

'capsstring-prefix?' ( c-addr1 u1 c-addr2 u2 -- f  ) gforth-1.0 "capsstring-prefix?"
   Like 'string-prefix?', but case-insensitive for ASCII characters: Is
C-ADDR2 U2 a prefix of C-ADDR1 U1?

'capssearch' ( c-addr1 u1 c-addr2 u2 -- c-addr3 u3 flag  ) gforth-1.0 "capssearch"
   Like 'search', but case-insensitive for ASCII characters: Search for
c-addr2 u2 in c-addr1 u1; flag is true if found.

   The following words create or extend strings on the heap:

's+' ( c-addr1 u1 c-addr2 u2 -- c-addr u  ) gforth-0.7 "s-plus"
   c-addr u is a newly 'allocate'd string that contains the
concatenation of c-addr1 u1 (first) and c-addr2 u2 (second).

'append' ( c-addr1 u1 c-addr2 u2 -- c-addr u  ) gforth-0.7 "append"
   C-addr u is the concatenation of c-addr1 u1 (first) and c-addr2 u2
(second).  c-addr1 u1 is an 'allocate'd string, and 'append' 'resize's
it (possibly moving it to a new address) to accomodate u characters.

'>string-execute' ( ... xt -- ... addr u  ) gforth-1.0 ">string-execute"
   execute xt while the standard output ('type', 'emit', and everything
that uses them) is redirected to a string.  The resulting string is addr
u, which is in 'allocate'd memory; it is the responsibility of the
caller of '>string-execute' to 'free' this string.

   One could define 's+' using '>string-execute', as follows:

   : s+ ( c-addr1 u1 c-addr2 u2 -- c-addr u ) [: 2swap type type ;]
>string-execute ;

   For concatenating just two strings '>string-execute' is inefficient,
but for concatenating many strings '>string-execute' can be more
efficient.

6.8.5 $tring words
------------------

The following string library stores strings in ordinary cell-size
variables (string handles).  These handles contain a pointer to a
cell-counted string allocated from the heap.  The string library
originates from bigFORTH.

   Because there is only one permanent reference to the contents (the
one in the handle), the string can be relocated or deleted without
worrying about dangling references; this requires that the programmer
uses references produced by, e.g., '$@' only for temporary purposes,
i.e., these references are not passed out, e.g., as return values or
stored in global memory, and words that may change the handle are not
called while these references exist.

   This library is complemented by the cell-pair representation: You use
the $tring words for variable strings which are cumbersome with the
c-addr u representation.  You use the cell-pair representation for
processing (e.g., inspecting) strings while they do not change.

'$!' ( addr1 u $addr --  ) gforth-0.7 "string-store"
   stores a newly allocated string buffer at an address, frees the
previous buffer if necessary.

'$@' ( $addr -- addr2 u  ) gforth-0.7 "string-fetch"
   returns the stored string.

'$@len' ( $addr -- u  ) gforth-0.7 "string-fetch-len"
   returns the length of the stored string.

'$!len' ( u $addr --  ) gforth-0.7 "string-store-len"
   changes the length of the stored string.  Therefore we must change
the memory area and adjust address and count cell as well.

'$+!len' ( u $addr -- addr  ) gforth-1.0 "string-plus-store-len"
   make room for u bytes at the end of the memory area referenced by
$addr; addr is the address of the first of these bytes.

'$del' ( addr off u --  ) gforth-0.7 "string-del"
   deletes U bytes from a string with offset OFF.

'$ins' ( addr1 u $addr off --  ) gforth-0.7 "string-ins"
   inserts a string at offset OFF.

'$+!' ( addr1 u $addr --  ) gforth-0.7 "string-plus-store"
   appends a string to another.

'c$+!' ( char $addr --  ) gforth-1.0 "c-string-plus-store"
   append a character to a string.

'$free' ( $addr --  ) gforth-1.0 "string-free"
   free the string pointed to by addr, and set addr to 0

'$init' ( $addr --  ) gforth-1.0 "string-init"
   store an empty string there, regardless of what was in before

'$split' ( addr u char -- addr1 u1 addr2 u2  ) gforth-0.7 "string-split"
   divides a string into two, with one char as separator (e.g.  '?' for
arguments in an HTML query)

'$iter' ( .. $addr char xt -- ..  ) gforth-0.7 "string-iter"
   takes a string apart piece for piece, also with a character as
separator.  For each part a passed token will be called.  With this you
can take apart arguments -- separated with '&' -- at ease.

'$over' ( addr u $addr off --  ) gforth-1.0 "string-over"
   overwrite string at offset off with addr u

'$exec' ( xt addr --  ) gforth-1.0 "string-exec"
   execute xt while the standard output (TYPE, EMIT, and everything that
uses them) is appended to the string variable addr.

'$tmp' ( xt -- addr u  ) gforth-1.0 "string-t-m-p"
   generate a temporary string from the output of a word

'$.' ( addr --  ) gforth-1.0 "string-dot"
   print a string, shortcut

'$slurp' ( fid addr --  ) gforth-1.0 "string-slurp"
   Read the file fid until the end (without closing it) and put the read
data into the string at addr.

'$slurp-file' ( c-addr u addr --  ) gforth-1.0 "string-slurp-file"
   Put all the data in the file named c-addr u into the string at addr.

'$+slurp' ( fid addr --  ) gforth-1.0 "string-plus-slurp"
   Read the file fid until the end (without closing it) and append the
read data to the string at addr.

'$+slurp-file' ( c-addr u addr --  ) gforth-1.0 "string-plus+slurp-file"
   Append all the data in the file named c-addr u to the string at addr.

'$[]' ( u $[]addr -- addr'  ) gforth-1.0 "string-array"
   Addr' is the address of the uth element of the string array $[]addr.
The array is resized if needed.

'$[]!' ( c-addr u n $[]addr --  ) gforth-1.0 "string-array-store"
   Store string c-addr y into the string array $[]addr at index n.  The
array is resized if needed.

'$[]+!' ( c-addr u n $[]addr --  ) gforth-1.0 "string-array-plus-store"
   Append the string c-addr u to the string at index n.  The array is
resized if needed.  Don't confuse this with '$+[]!'.

'$+[]!' ( c-addr u $[]addr --  ) gforth-1.0 "string-append-array"
   Store the string c-addr u as the new last element of string array
$[]addr.  The array is resized if needed.

'$[]@' ( n $[]addr -- addr u  ) gforth-1.0 "string-array-fetch"
   fetch a string from array index n --- return the zero string if empty,
and don't accidentally grow the array.

'$[]#' ( addr -- len  ) gforth-1.0 "string-array-num"
   return the number of elements in an array

'$[]map' ( addr xt --  ) gforth-1.0 "string-array-map"
   execute XT for all elements of the string array ADDR.  xt is ( ADDR U
-- ), getting one string at a time

'$[]slurp' ( fid addr --  ) gforth-1.0 "string-array-slurp"
   slurp a file FID line by line into a string array ADDR

'$[]slurp-file' ( addr u $addr --  ) gforth-1.0 "string-array-slurp-file"
   slurp a named file ADDR U line by line into a string array $ADDR

'$[].' ( addr --  ) gforth-1.0 "string-array-dot"
   print all array entries

'$[]free' ( addr --  ) gforth-1.0 "string-array-free"
   addr contains the address of a cell-counted string that contains the
addresses of a number of cell-counted strings; $[]free frees these
strings, frees the array, and sets addr to 0

'$save' ( $addr --  ) gforth-1.0 "string-save"
   push string to dictionary for savesys

'$[]save' ( addr --  ) gforth-1.0 "string-array-save"
   push string array to dictionary for savesys

'$boot' ( $addr --  ) gforth-1.0 "string-boot"
   take string from dictionary to allocated memory.  clean dictionary
afterwards.

'$[]boot' ( addr --  ) gforth-1.0 "string-array-boot"
   take string array from dictionary to allocated memory

'$saved' ( addr --  ) gforth-1.0 "string-saved"
   mark an address as booted/saved

'$[]saved' ( addr --  ) gforth-1.0 "string-array-saved"
   mark an address as booted/saved

'$Variable' ( --  ) gforth-1.0 "string-variable"
   A string variable which is preserved across savesystem

'$[]Variable' ( --  ) gforth-1.0 "string-array-variable"
   A string variable which is preserved across savesystem

6.8.6 Counted string words
--------------------------

Counted strings store the length as byte at the address pointed to,
followed by the bytes of the string.  Their possible length is severely
limited, and you cannot create a substring in-place without destroying
the input string.  Therefore we recommend against using counted strings.
Nevertheless, if you have to deal with counted strings, here are some
words for that:

'count' ( c-addr1 -- c-addr2 u ) core "count"
   c-addr2 is the first character and u the length of the counted string
at c-addr1.

   The following word has no useful interpretation semantics (unlike
's"') and no interpretive counterpart (unlike '[char]'), so you should
use it only inside colon definitions (if at all):

'C"' ( compilation "ccc<quote>" -- ; run-time  -- c-addr  ) core-ext "c-quote"
   Compilation: parse a string ccc delimited by a '"' (double quote).
At run-time, return c-addr which specifies the counted string ccc.
Interpretation semantics are undefined.

   doc-place
'string,' ( c-addr u --  ) gforth-0.2 "string,"
   puts down string as cstring

6.9 Control Structures
======================

Control structures in Forth cannot be used interpretively, only in a
colon definition(1).  We do not like this limitation, but have not seen
a satisfying way around it yet, although many schemes have been
proposed.

   ---------- Footnotes ----------

   (1) To be precise, they have no interpretation semantics (*note
Interpretation and Compilation Semantics::).

6.9.1 Selection
---------------

     flag
     IF
       code
     ENDIF

   If flag is non-zero (as far as 'IF' etc.  are concerned, a cell with
any bit set represents truth) code is executed.

     flag
     IF
       code1
     ELSE
       code2
     ENDIF

   If FLAG is true, code1 is executed, otherwise code2 is executed.

   You can use 'THEN' instead of 'ENDIF'.  Indeed, 'THEN' is standard,
and 'ENDIF' is not, although it is quite popular.  We recommend using
'ENDIF', because it is less confusing for people who also know other
languages (and is not prone to reinforcing negative prejudices against
Forth in these people).  Adding 'ENDIF' to a system that only supplies
'THEN' is simple:
     : ENDIF   POSTPONE then ; immediate

   [According to 'Webster's New Encyclopedic Dictionary', "then (adv.)"
has the following meanings:
     ...  2b: following next after in order ...  3d: as a necessary
     consequence (if you were there, then you saw them).
   Forth's 'THEN' has the meaning 2b, whereas 'THEN' in Pascal and many
other programming languages has the meaning 3d.]

   Gforth also provides the words '?DUP-IF' and '?DUP-0=-IF', so you can
avoid using '?dup'.  Using these alternatives is also more efficient
than using '?dup'.  Definitions in Standard Forth for 'ENDIF', '?DUP-IF'
and '?DUP-0=-IF' are provided in 'compat/control.fs'.

     x
     CASE
       x1 OF code1 ENDOF
       x2 OF code2 ENDOF
       ...
       ( x ) default-code ( x )
     ENDCASE ( )

   Executes the first codei, where the xi is equal to x.  If no xi
matches, the optional default-code is executed.  The optional default
case can be added by simply writing the code after the last 'ENDOF'.  It
may use x, which is on top of the stack, but must not consume it.  The
value x is consumed by this construction (either by an 'OF' that
matches, or by the 'ENDCASE', if no OF matches).  Example:

     : num-name ( n -- c-addr u )
      case
        0 of s" zero " endof
        1 of s" one "  endof
        2 of s" two "  endof
        \ default case:
        s" other number"
        rot \ get n on top so ENDCASE can drop it
      endcase ;

   You can also use (the non-standard) '?of' to use 'case' as a general
selection structure for more than two alternatives.  '?Of' takes a flag.
Example:

     : sgn ( n1 -- n2 )
         \ sign function
         case
     	dup 0< ?of drop -1 endof
     	dup 0> ?of drop 1 endof
     	dup \ n1=0 -> n2=0; dup an item, to be consumed by ENDCASE
         endcase ;

   Programming style note:

   To keep the code understandable, you should ensure that you change
the stack in the same way (wrt.  number and types of stack items
consumed and pushed) on all paths through a selection structure.

6.9.2 Simple Loops
------------------

     BEGIN
       code1
       flag
     WHILE
       code2
     REPEAT

   code1 is executed and flag is computed.  If it is true, code2 is
executed and the loop is restarted; If flag is false, execution
continues after the 'REPEAT'.

     BEGIN
       code
       flag
     UNTIL

   code is executed.  The loop is restarted if 'flag' is false.

   Programming style note:

   To keep the code understandable, a complete iteration of the loop
should not change the number and types of the items on the stacks.

     BEGIN
       code
     AGAIN

   This is an endless loop.

6.9.3 Counted Loops
-------------------

The basic counted loop is:
     limit start ?DO
       body
     LOOP

   This performs one iteration for every integer, starting from start
and up to, but excluding limit.  The counter, or index, can be accessed
with 'i'.  For example, the loop:
     10 0 ?DO
       i .
     LOOP
prints '0 1 2 3 4 5 6 7 8 9'

   The index of the innermost loop can be accessed with 'i', the index
of the next loop with 'j', and the index of the third loop with 'k'.

   You can access the limit of the innermost loop with 'i'' and 'i''-'i'
with 'delta-i'.  E.g., running

     : foo 7 5 ?do cr i . i' . delta-i . loop ;

   prints

     5 7 2
     6 7 1

   The loop control data are kept on the return stack, so there are some
restrictions on mixing return stack accesses and counted loop words.  In
particuler, if you put values on the return stack outside the loop, you
cannot read them inside the loop(1).  If you put values on the return
stack within a loop, you have to remove them before the end of the loop
and before accessing the index of the loop.

   There are several variations on the counted loop:

   * 'LEAVE' leaves the innermost counted loop immediately; execution
     continues after the associated 'LOOP' or 'NEXT'.  For example:

          10 0 ?DO  i DUP . 3 = IF LEAVE THEN LOOP
     prints '0 1 2 3'

   * 'UNLOOP' prepares for an abnormal loop exit, e.g., via 'EXIT'.
     'UNLOOP' removes the loop control parameters from the return stack
     so 'EXIT' can get to its return address.  For example:

          : demo 10 0 ?DO i DUP . 3 = IF UNLOOP EXIT THEN LOOP ." Done" ;
     prints '0 1 2 3'

   * If start is greater than limit, a '?DO' loop is entered (and 'LOOP'
     iterates until they become equal by wrap-around arithmetic).  This
     behaviour is usually not what you want.  Therefore, Gforth offers
     '+DO' and 'U+DO' (as replacements for '?DO'), which do not enter
     the loop if start is greater than limit; '+DO' is for signed loop
     parameters, 'U+DO' for unsigned loop parameters.

   * '?DO' can be replaced by 'DO'.  'DO' always enters the loop,
     independent of the loop parameters.  Do not use 'DO', even if you
     know that the loop is entered in any case.  Such knowledge tends to
     become invalid during maintenance of a program, and then the 'DO'
     will make trouble.

   * 'LOOP' can be replaced with 'n +LOOP'; this updates the index by n
     instead of by 1.  The loop is terminated when the border between
     limit-1 and limit is crossed.  E.g.:

          4 0 +DO  i .  2 +LOOP
     prints '0 2'

          4 1 +DO  i .  2 +LOOP
     prints '1 3'

   * The behaviour of 'n +LOOP' is peculiar when n is negative:

          -1 0 ?DO  i .  -1 +LOOP
     prints '0 -1'

          0 0 ?DO  i .  -1 +LOOP
     prints nothing.

     We recommend not combining '?DO' with '+LOOP'.  Gforth offers
     several alternatives:

     If you want '-1 +LOOP''s behaviour of including an iteration where
     'I'=limit, start the loop with '-[DO' or 'U-[DO' (where the '[' is
     inspired by the mathematical notation for inclusive ranges, e.g.,
     [1,n]):

          -1 0 -[DO  i .  -1 +LOOP

     prints '0 -1'.

          0 0 -[DO  i .  -1 +LOOP

     prints '0'.

          0 -1 -[DO  i .  -1 +LOOP

     prints nothing.

     If you want to exclude the limit, you instead use '1 -LOOP' (or
     generally 'u -LOOP') and start the loop with '?DO', '-DO' or
     'U-DO'.  '-LOOP' terminates the loop when the border between
     limit+1 and limit is crossed.  E.g.:

          -2 0 -DO  i .  1 -LOOP
     prints '0 -1'

          -1 0 -DO  i .  1 -LOOP
     prints '0'

          0 0 -DO  i .  1 -LOOP
     prints nothing.

     Unfortunately, '+DO', 'U+DO', '-DO', 'U-DO' and '-LOOP' are not
     defined in Standard Forth.  However, an implementation for these
     words that uses only standard words is provided in
     'compat/loops.fs'.

   * A common task is to iterate over the elements of an array, forwards
     or backwards.  Iterating over the addresses of the elements has two
     benefits: It avoids the need to keep the start address of the array
     around, reducing the data stack load; and it avoids the need to
     perform address computations in every iteration.  The disadvantage
     is that, starting with the usual array representations addr uelems
     or addr ubytes, some processing is required to produce a start and
     limit address.  Gforth has 'bounds' for getting there from the addr
     ubytes representation, so you can write a forward loop through a
     cell array 'v' as:

          create v 1 , 3 , 7 ,
          : foo v 3 cells bounds U+DO i  . cell +LOOP ;
          foo

     which prints '1 3 7'.  Preprocessing the inputs for walking
     backwards is more involved, so Gforth provide a loop construct of
     the form 'MEM-DO'...'LOOP' that does it for you: It takes an array
     in addr ubytes representation and the element size, and iterates
     over the addresses of the elements in backwards order:

          create v 1 , 3 , 7 ,
          : foo1 v 3 cell array>mem MEM-DO i  . LOOP ;
          foo1

     This prints '7 3 1'.  'ARRAY>MEM' converts the addr uelems
     uelemsize representation into the addr ubytes uelemsize
     representation expected by 'MEM-DO'.  This loop is finished with
     'LOOP' which decrements by uelemsize when it finishes a 'MEM-DO'.

     Gforth also adds 'MEM+DO' for completeness.  It takes the same
     parameters as 'MEM-DO', but walks forwards through the array:

          create v 1 , 3 , 7 ,
          : foo2 v 3 cell array>mem MEM+DO i  . LOOP ;
          foo2

     prints '1 3 7'.

   * Another counted loop is:
          n
          FOR
            body
          NEXT
     This is the preferred loop of native code compiler writers who are
     too lazy to optimize '?DO' loops properly.  This loop structure is
     not defined in Standard Forth.  In Gforth, this loop iterates n+1
     times; 'i' produces values starting with n and ending with 0.
     Other Forth systems may behave differently, even if they support
     'FOR' loops.  To avoid problems, don't use 'FOR' loops.

   The counted-loop words are:

'?DO' ( compilation -- do-sys ; run-time w1 w2 -- | loop-sys  ) core-ext "question-do"
   *Note Counted Loops::.

'+DO' ( compilation -- do-sys ; run-time n1 n2 -- | loop-sys  ) gforth-0.2 "plus-do"
   *Note Counted Loops::.

'U+DO' ( compilation -- do-sys ; run-time u1 u2 -- | loop-sys  ) gforth-0.2 "u-plus-do"
   *Note Counted Loops::.

'bounds' ( u1 u2 -- u3 u1 ) gforth-0.2 "bounds"
   Given a memory block represented by starting address addr and length
u in aus, produce the end address addr+u and the start address in the
right order for 'u+do' or '?do'.

'-[do' ( compilation -- do-sys ; run-time n1 n2 -- | loop-sys  ) gforth-experimental "minus-bracket-do"
   Start of a counted loop with negative stride; Skips the loop if
n2<n1; such a counted loop ends with '+loop' where the increment is
negative; it runs as long as 'I'>=n1.

'u-[do' ( compilation -- do-sys ; run-time u1 u2 -- | loop-sys  ) gforth-experimental "u-minus-bracket-do"
   Start of a counted loop with negative stride; Skips the loop if
u2<u1; such a counted loop ends with '+loop' where the increment is
negative; it runs as long as 'I'>=u1.

'-DO' ( compilation -- do-sys ; run-time n1 n2 -- | loop-sys  ) gforth-0.2 "minus-do"
   *Note Counted Loops::.

'U-DO' ( compilation -- do-sys ; run-time u1 u2 -- | loop-sys  ) gforth-0.2 "u-minus-do"
   *Note Counted Loops::.

   doc-array>mem
'mem+do' ( compilation -- w xt do-sys; run-time addr ubytes +nstride --  ) gforth-experimental "mem-plus-do"
   Starts a counted loop that starts with 'I' as addr and then steps
upwards through memory with nstride wide steps as long as
'I'<addr+ubytes.  Must be finished with loop.

'mem-do' ( compilation -- w xt do-sys; run-time addr ubytes +nstride --  ) gforth-experimental "mem-minus-do"
   Starts a counted loop that starts with 'I' as addr+ubytes-ustride and
then steps backwards through memory with -nstride wide steps as long as
'I'>=addr.  Must be finished with loop.

'DO' ( compilation -- do-sys ; run-time w1 w2 -- loop-sys  ) core "DO"
   *Note Counted Loops::.

'FOR' ( compilation -- do-sys ; run-time u -- loop-sys  ) gforth-0.2 "FOR"
   *Note Counted Loops::.

'LOOP' ( compilation do-sys -- ; run-time loop-sys1 -- | loop-sys2  ) core "LOOP"
   *Note Counted Loops::.

'+LOOP' ( compilation do-sys -- ; run-time loop-sys1 n -- | loop-sys2  ) core "plus-loop"
   *Note Counted Loops::.

'-LOOP' ( compilation do-sys -- ; run-time loop-sys1 u -- | loop-sys2  ) gforth-0.2 "minus-loop"
   *Note Counted Loops::.

'NEXT' ( compilation do-sys -- ; run-time loop-sys1 -- | loop-sys2  ) gforth-0.2 "NEXT"
   *Note Counted Loops::.

'i' ( R:n -- R:n n ) core "i"
   n is the index of the innermost counted loop.

'j' ( R:n R:w1 R:w2 -- n R:n R:w1 R:w2 ) core "j"
   n is the index of the next-to-innermost counted loop.

'k' ( R:n R:w1 R:w2 R:w3 R:w4 -- n R:n R:w1 R:w2 R:w3 R:w4 ) gforth-0.3 "k"
   n is the index of the third-innermost counted loop.

'i'' ( R:w R:w2 -- R:w R:w2 w ) gforth-0.2 "i-tick"
   The limit of the innermost counted loop

'delta-i' ( r:ulimit r:u -- r:ulimit r:u u2 ) gforth-1.0 "delta-i"
   u2='I''-'I' (difference between limit and index).

'LEAVE' ( compilation -- ; run-time loop-sys --  ) core "LEAVE"
   *Note Counted Loops::.

'?LEAVE' ( compilation -- ; run-time f | f loop-sys --  ) gforth-0.2 "question-leave"
   *Note Counted Loops::.

'unloop' ( R:w1 R:w2 -- ) core "unloop"

'DONE' ( compilation do-sys -- ; run-time --  ) gforth-0.2 "DONE"
   resolves all LEAVEs up to the do-sys

   The standard does not allow using 'CS-PICK' and 'CS-ROLL' on do-sys.
Gforth allows it, except for the do-sys produced by 'MEM+DO' and
'MEM-DO', but it's your job to ensure that for every '?DO' etc.  there
is exactly one 'UNLOOP' on any path through the definition ('LOOP' etc.
compile an 'UNLOOP' on the fall-through path).  Also, you have to ensure
that all 'LEAVE's are resolved (by using one of the loop-ending words or
'DONE').

   ---------- Footnotes ----------

   (1) well, not in a way that is portable.

6.9.4 'Begin' loops with multiple exits
---------------------------------------

For counted loops, you can use 'leave' in several places.  For 'begin'
loops, you have the following options:

   Use 'exit' (possibly several times) in the loop to leave not just the
loop, but the whole colon definition.  E.g.,:

     : foo
       begin
         condition1 while
           condition2 if
             exit-code2 exit then
           condition3 if
             exit-code3 exit then
         ...
       repeat
       exit-code1 ;

   The disadvantage of this approach is that, if you want to have some
common code afterwards, you either have to wrap 'foo' in another word
that contains the common code, or you have to call the common code
several times, from each exit-code.

   Another approach is to use several 'while's in a 'begin' loop.  You
have to append a 'then' behind the loop for every additional 'while'.
E.g.,;

     begin
       condition1 while
         condition2 while
           condition3 while
     again then then then

   Here I used 'again' at the end of the loop so that I would have a
'then' for each 'while'; 'repeat' would result in one less 'then', but
otherwise the same behaviour.  For an explanation of why this works,
*Note Arbitrary control structures::.

   We can have common code afterwards, but, as presented above, we
cannot have different exit-codes for the different exits.  You can have
these different exit-codes, as follows:

     begin
       condition1 while
         condition2 while
           condition3 while
     again then exit-code3
     else exit-code2 then
     else exit-code1 then

   This is relatively hard to comprehend, because the exit-codes are
relatively far from the exit conditions (it does not help that we are
not used to such control structures, either).

6.9.5 General control structures with 'case'
--------------------------------------------

Gforth provides an extended 'case' that solves the problems of the
multi-exit loops discussed above, and offers additional options.  You
can find a portable implementation of this extended 'case' in
'compat/caseext.fs'.

   There are three additional words in the extension.  The first is
'?of' which allows general tests (rather than just testing for equality)
in a 'case'; e.g.,

     : sgn ( n -- -1|0|1 )
       ( n ) case
         dup 0 < ?of drop -1 endof
         dup 0 > ?of drop 1  endof
         \ otherwise leave the 0 on the stack
       0 endcase ;

   Note that 'endcase' drops a value, which works fine much of the time
with 'of', but usually not with '?of', so we leave a 0 on the stack for
'endcase' to drop.  The n that is passed into 'sgn' is also 0 if neither
'?of' triggers, and that is then passed out.

   The second additional word is 'next-case', which allows turning
'case' into a loop.  Our triple-exit loop becomes:

     case
       condition1 ?of exit-code1 endof
       condition2 ?of exit-code2 endof
       condition3 ?of exit-code3 endof
       ...
     next-case
     common code afterwards

   As you can see, this solves both problems of the variants discussed
above (*note BEGIN loops with multiple exits::).  Note that 'next-case'
does not drop a value, unlike 'endcase'.(1)

   The last additional word is 'contof', which is used instead of
'endof' and starts the next iteration instead of leaving the loop.  This
can be used in ways similar to Dijkstra's guarded command do, e.g.:

     : gcd ( n1 n2 -- n )
         case
             2dup > ?of tuck - contof
             2dup < ?of over - contof
         endcase ;

   Here the two '?of's have different ways of continuing the loop; when
neither '?of' triggers, the two numbers are equal and are the gcd.
'Endcase' drops one of them, leaving the other as n.

   You can also combine these words.  Here's an example that uses each
of the 'case' words once, except 'endcase':

     : collatz ( u -- )
         \ print the 3n+1 sequence starting at u until we reach 1
         case
             dup .
             1 of endof
             dup 1 and ?of 3 * 1+ contof
             2/
         next-case ;

   This example keeps the current value of the sequence on the stack.
If it is 1, the 'of' triggers, drops the value, and leaves the 'case'
structure.  For odd numbers, the '?of' triggers, computes 3n+1, and
starts the next iteration with 'contof'.  Otherwise, if the number is
even, it is divided by 2, and the loop is restarted with 'next-case'.

   ---------- Footnotes ----------

   (1) 'Next-case' has a '-', unlike the other 'case' words, because VFX
Forth contains a 'nextcase' that drops a value.

6.9.6 Arbitrary control structures
----------------------------------

Standard Forth permits and supports using control structures in a
non-nested way.  Information about incomplete control structures is
stored on the control-flow stack.  This stack may be implemented on the
Forth data stack, and this is what we have done in Gforth.

   An orig entry represents an unresolved forward branch, a dest entry
represents a backward branch target.  A few words are the basis for
building any control structure possible (except control structures that
need storage, like calls, coroutines, and backtracking).

'IF' ( compilation -- orig ; run-time f --  ) core "IF"
   At run-time, if f=0, execution continues after the 'THEN' (or 'ELSE')
that consumes the orig, otherwise right after the 'IF' (*note
Selection::).

'AHEAD' ( compilation -- orig ; run-time --  ) tools-ext "AHEAD"
   At run-time, execution continues after the 'THEN' that consumes the
orig.

'THEN' ( compilation orig -- ; run-time --  ) core "THEN"
   The 'IF', 'AHEAD', 'ELSE' or 'WHILE' that pushed orig jumps right
after the 'THEN' (*note Selection::).

'BEGIN' ( compilation -- dest ; run-time --  ) core "BEGIN"
   The 'UNTIL', 'AGAIN' or 'REPEAT' that consumes the dest jumps right
behind the 'BEGIN' (*note Simple Loops::).

'UNTIL' ( compilation dest -- ; run-time f --  ) core "UNTIL"
   At run-time, if f=0, execution continues after the 'BEGIN' that
produced dest, otherwise right after the 'UNTIL' (*note Simple Loops::).

'AGAIN' ( compilation dest -- ; run-time --  ) core-ext "AGAIN"
   At run-time, execution continues after the 'BEGIN' that produced the
dest (*note Simple Loops::).

'CS-PICK' ( orig0/dest0 orig1/dest1 ... origu/destu u -- ... orig0/dest0  ) tools-ext "c-s-pick"

'CS-ROLL' ( destu/origu .. dest0/orig0 u -- .. dest0/orig0 destu/origu  ) tools-ext "c-s-roll"

'CS-DROP' ( dest --  ) gforth-1.0 "CS-DROP"

   The Standard words 'CS-PICK' and 'CS-ROLL' allow you to manipulate
the control-flow stack in a portable way.  Without them, you would need
to know how many stack items are occupied by a control-flow entry (many
systems use one cell.  In Gforth they currently take three, but this may
change in the future).

   'CS-PICK' can only pick a dest and 'CS-DROP' can only drop a dest,
because an orig must be resolved exactly once.

   Some standard control structure words are built from these words:

'ELSE' ( compilation orig1 -- orig2 ; run-time --  ) core "ELSE"
   At run-time, execution continues after the 'THEN' that consumes the
orig; the 'IF', 'AHEAD', 'ELSE' or 'WHILE' that pushed orig1 jumps right
after the 'ELSE'.  (*note Selection::).

'WHILE' ( compilation dest -- orig dest ; run-time f --  ) core "WHILE"
   At run-time, if f=0, execution continues after the 'REPEAT' (or
'THEN' or 'ELSE') that consumes the orig, otherwise right after the
'WHILE' (*note Simple Loops::).

'REPEAT' ( compilation orig dest -- ; run-time --  ) core "REPEAT"
   At run-time, execution continues after the 'BEGIN' that produced the
dest; the 'WHILE', 'IF', 'AHEAD' or 'ELSE' that pushed orig jumps right
after the 'REPEAT'.  (*note Simple Loops::).

Gforth adds some more control-structure words:

'ENDIF' ( compilation orig -- ; run-time --  ) gforth-0.2 "ENDIF"
   Same as 'THEN'.

'?dup-IF' ( compilation -- orig ; run-time n -- n|  ) gforth-0.2 "question-dupe-if"
   This is the preferred alternative to the idiom "'?DUP IF'", since it
can be better handled by tools like stack checkers.  Besides, it's
faster.

'?DUP-0=-IF' ( compilation -- orig ; run-time n -- n|  ) gforth-0.2 "question-dupe-zero-equals-if"

Another group of control structure words are:

'case' ( compilation  -- case-sys ; run-time  --  ) core-ext "case"
   Start a 'case' structure.

'endcase' ( compilation case-sys -- ; run-time x --  ) core-ext "end-case"
   Finish the 'case' structure; drop x, and continue behind the
'endcase'.  Dropping x is useful in the original 'case' construct (with
only 'of's), but you may have to supply an x in other cases (especially
when using '?of').

'next-case' ( compilation case-sys -- ; run-time --  ) gforth-1.0 "next-case"
   Restart the 'case' loop by jumping to the matching 'case'.  Note that
'next-case' does not drop a cell, unlike 'endcase'.

'of' ( compilation  -- of-sys ; run-time x1 x2 -- |x1  ) core-ext "of"
   If x1=x2, continue (dropping both); otherwise, leave x1 on the stack
and jump behind 'endof' or 'contof'.

'?of' ( compilation  -- of-sys ; run-time  f --  ) gforth-1.0 "question-of"
   If f is true, continue; otherwise, jump behind 'endof' or 'contof'.

'endof' ( compilation case-sys1 of-sys -- case-sys2 ; run-time  --  ) core-ext "end-of"
   Exit the enclosing 'case' structure by jumping behind
'endcase'/'next-case'.

'contof' ( compilation case-sys1 of-sys -- case-sys2 ; run-time  --  ) gforth-1.0 "cont-of"
   Restart the 'case' loop by jumping to the enclosing 'case'.

   Internally, of-sys is an 'orig'; and case-sys is a cell and some
stack-depth information, 0 or more 'orig's, and a 'dest'.

6.9.6.1 Programming Style
.........................

In order to ensure readability we recommend that you do not create
arbitrary control structures directly, but define new control structure
words for the control structure you want and use these words in your
program.  For example, instead of writing:

     BEGIN
       ...
     IF [ 1 CS-ROLL ]
       ...
     AGAIN THEN

we recommend defining control structure words, e.g.,

     : WHILE ( DEST -- ORIG DEST )
      POSTPONE IF
      1 CS-ROLL ; immediate

     : REPEAT ( orig dest -- )
      POSTPONE AGAIN
      POSTPONE THEN ; immediate

and then using these to create the control structure:

     BEGIN
       ...
     WHILE
       ...
     REPEAT

   That's much easier to read, isn't it?  Of course, 'REPEAT' and
'WHILE' are predefined, so in this example it would not be necessary to
define them.

6.9.7 Calls and returns
-----------------------

A definition can be called simply be writing the name of the definition
to be called.  Normally a definition is invisible during its own
definition.  If you want to write a directly recursive definition, you
can use 'recursive' to make the current definition visible, or 'recurse'
to call the current definition directly.

'recursive' ( compilation -- ; run-time --  ) gforth-0.2 "recursive"
   Make the current definition visible, enabling it to call itself
recursively.

'recurse' ( ... -- ...  ) core "recurse"
   Alias to the current definition.

For examples of using these words, *Note Recursion Tutorial::.

   Programming style note:

   I prefer using 'recursive' to 'recurse', because calling the
definition by name is more descriptive (if the name is well-chosen) than
the somewhat cryptic 'recurse'.  E.g., in a quicksort implementation, it
is much better to read (and think) "now sort the partitions" than to
read "now do a recursive call".

   For mutual recursion, use 'Defer'red words, like this:

     Defer foo

     : bar ( ... -- ... )
      ... foo ... ;

     :noname ( ... -- ... )
      ... bar ... ;
     IS foo

   Deferred words are discussed in more detail in *note Deferred
Words::.

   The current definition returns control to the calling definition when
the end of the definition is reached or 'EXIT' is encountered.

'EXIT' ( compilation -- ; run-time nest-sys --  ) core "EXIT"
   Return to the calling definition; usually used as a way of forcing an
early return from a definition.  Before 'EXIT'ing you must clean up the
return stack and 'UNLOOP' any outstanding '?DO'...'LOOP's.  Use ';s' for
a tickable word that behaves like 'exit' in the absence of locals.

'?EXIT' ( --  ) gforth-0.2 "?EXIT"
   Return to the calling definition if f is true.

';s' ( R:w -- ) gforth-0.2 "semis"
   The primitive compiled by 'EXIT'.

6.9.8 Exception Handling
------------------------

If a word detects an error condition that it cannot handle, it can
'throw' an exception.  In the simplest case, this will terminate your
program, and report an appropriate error.

'throw' ( y1 .. ym nerror -- y1 .. ym / z1 .. zn error  ) exception "throw"
   If nerror is 0, drop it and continue.  Otherwise, transfer control to
the next dynamically enclosing exception handler, reset the stacks
accordingly, and push nerror.

'fast-throw' ( ... wball -- ... wball ) gforth-experimental "fast-throw"
   Lightweight 'throw' variant: only for non-zero balls, and does not
store a backtrace or deal with missing 'catch'.

   'Throw' consumes a cell-sized error number on the stack.  There are
some predefined error numbers in Standard Forth (see 'errors.fs').  In
Gforth (and most other systems) you can use the iors produced by various
words as error numbers (e.g., a typical use of 'allocate' is 'allocate
throw').  Gforth also provides the word 'exception' to define your own
error numbers (with decent error reporting); a Standard Forth version of
this word (but without the error messages) is available in
'compat/except.fs'.  And finally, you can use your own error numbers
(anything outside the range -4095..0), but won't get nice error
messages, only numbers.  For example, try:

     -10 throw                    \ Standard defined
     -267 throw                   \ system defined
     s" my error" exception throw \ user defined
     7 throw                      \ arbitrary number

'exception' ( addr u -- n  ) gforth-0.2 "exception"
   N is a previously unused 'throw' value in the range (-4095...-256).
Consecutive calls to 'exception' return consecutive decreasing numbers.
Gforth uses the string ADDR U as an error message.

   There are also cases where you have a word (typically modeled after
POSIX' 'strerror') for converting an error number into a string.  You
can use the following word to get these strings into Gforth's error
handling:

'exceptions' ( xt n1 -- n2  ) gforth-1.0 "exceptions"
   Xt '( +n -- c-addr u )' converts an error number in the range 0<=n<n1
into an error message.  'Exceptions' reserves n1 error codes in the
range n2-n1<n3<=n2.  When (at some later point in time) the Gforth error
code n3 in that range is thrown, it pushes n2-n3 and then executes xt to
produce the error message.

   As an example, if the 'errno' errors (and the conversion using
'strerror') was not already directly supported by Gforth, you could tie
'strerror' in as follows:

     ' strerror 1536 exceptions constant errno-base
     : errno-ior ( -- n )
     \ n is the Gforth ior corresponding to the value in errno, so
     \ we have to convert between the ranges here.
     \ ERRNO is not a Gforth word, so you  would have to use the
     \ C interface to access it.
       errno errno-base over - swap 0<> and ;

   When you call a C function (with the C interface) and its return
value indictes that an error happened, you can then perform 'errno-ior
throw' to produce an exception with the proper error message (such as
"Permission denied").

   A common idiom to 'THROW' a specific err# if a flag is true is this:

     ( flag ) 0<> err# and throw

   Your program can provide exception handlers to catch exceptions.  An
exception handler can be used to correct the problem, or to clean up
some data structures and just throw the exception to the next exception
handler.  Note that 'throw' jumps to the dynamically innermost exception
handler.  The system's exception handler is outermost, and just prints
an error and restarts command-line interpretation (or, in batch mode
(i.e., while processing the shell command line), leaves Gforth).

   The Standard Forth way to catch exceptions is 'catch':

'catch' ( x1 .. xn xt -- y1 .. ym 0 / z1 .. zn error  ) exception "catch"
   'Executes' xt.  If execution returns normally, 'catch' pushes 0 on
the stack.  If execution returns through 'throw', all the stacks are
reset to the depth on entry to 'catch', and the TOS (the xt position) is
replaced with the throw code.

'nothrow' ( --  ) gforth-0.7 "nothrow"
   Use this (or the standard sequence '['] false catch 2drop') after a
'catch' or 'endtry' that does not rethrow; this ensures that the next
'throw' will record a backtrace.

   The most common use of exception handlers is to clean up the state
when an error happens.  E.g.,

     base @ >r hex \ actually the HEX should be inside foo to protect
                   \ against exceptions between HEX and CATCH
     ['] foo catch ( nerror|0 )
     r> base !
     ( nerror|0 ) throw \ pass it on

   A use of 'catch' for handling the error 'myerror' might look like
this:

     ['] foo catch
     CASE
       myerror OF ... ( do something about it ) nothrow ENDOF
       dup throw \ default: pass other errors on, do nothing on non-errors
     ENDCASE

   Having to wrap the code into a separate word is often cumbersome,
therefore Gforth provides an alternative syntax:

     TRY
       code1
       IFERROR
         code2
       THEN
       code3
     ENDTRY

   This performs code1.  If code1 completes normally, execution
continues with code3.  If there is an exception in code1 or before
'endtry', the stacks are reset to the depth during 'try', the throw
value is pushed on the data stack, and execution continues at code2, and
finally falls through to code3.

'try' ( compilation  -- orig ; run-time  -- R:sys1  ) gforth-0.5 "try"
   Start an exception-catching region.

'endtry' ( compilation  -- ; run-time  R:sys1 --  ) gforth-0.5 "endtry"
   End an exception-catching region.

'iferror' ( compilation  orig1 -- orig2 ; run-time  --  ) gforth-0.7 "iferror"
   Starts the exception handling code (executed if there is an exception
between 'try' and 'endtry').  This part has to be finished with 'then'.

   If you don't need code2, you can write 'restore' instead of 'iferror
then':

     TRY
       code1
     RESTORE
       code3
     ENDTRY

   The cleanup example from above in this syntax:

     base @ { oldbase }
     TRY
       hex foo \ now the hex is placed correctly
       0       \ value for throw
     RESTORE
       oldbase base !
     ENDTRY
     throw

   An additional advantage of this variant is that an exception between
'restore' and 'endtry' (e.g., from the user pressing 'Ctrl-C') restarts
the execution of the code after 'restore', so the base will be restored
under all circumstances.

   However, you have to ensure that this code does not cause an
exception itself, otherwise the 'iferror'/'restore' code will loop.
Moreover, you should also make sure that the stack contents needed by
the 'iferror'/'restore' code exist everywhere between 'try' and
'endtry'; in our example this is achived by putting the data in a local
before the 'try' (you cannot use the return stack because the exception
frame (sys1) is in the way there).

   This kind of usage corresponds to Lisp's 'unwind-protect'.

   If you do not want this exception-restarting behaviour, you achieve
this as follows:

     TRY
       code1
     ENDTRY-IFERROR
       code2
     THEN

   If there is an exception in code1, then code2 is executed, otherwise
execution continues behind the 'then' (or in a possible 'else' branch).
This corresponds to the construct

     TRY
       code1
     RECOVER
       code2
     ENDTRY

   in Gforth before version 0.7.  So you can directly replace
'recover'-using code; however, we recommend that you check if it would
not be better to use one of the other 'try' variants while you are at
it.

   To ease the transition, Gforth provides two compatibility files:
'endtry-iferror.fs' provides the 'try ... endtry-iferror ... then'
syntax (but not 'iferror' or 'restore') for old systems;
'recover-endtry.fs' provides the 'try ... recover ... endtry' syntax on
new systems, so you can use that file as a stopgap to run old programs.
Both files work on any system (they just do nothing if the system
already has the syntax it implements), so you can unconditionally
'require' one of these files, even if you use a mix old and new systems.

'restore' ( compilation  orig1 -- ; run-time  --  ) gforth-0.7 "restore"
   Starts restoring code, that is executed if there is an exception, and
if there is no exception.

'endtry-iferror' ( compilation  orig1 -- orig2 ; run-time  R:sys1 --  ) gforth-0.7 "endtry-iferror"
   End an exception-catching region while starting exception-handling
code outside that region (executed if there is an exception between
'try' and 'endtry-iferror').  This part has to be finished with 'then'
(or 'else'...'then').

   Here's the error handling example:

     TRY
       foo
     ENDTRY-IFERROR
       CASE
         myerror OF ... ( do something about it ) nothrow ENDOF
         throw \ pass other errors on
       ENDCASE
     THEN

   Programming style note:

   As usual, you should ensure that the stack depth is statically known
at the end: either after the 'throw' for passing on errors, or after the
'ENDTRY' (or, if you use 'catch', after the end of the selection
construct for handling the error).

   There are two alternatives to 'throw': 'Abort"' is conditional and
you can provide an error message.  'Abort' just produces an "Aborted"
error.

   The problem with these words is that exception handlers cannot
differentiate between different 'abort"'s; they just look like '-2
throw' to them (the error message cannot be accessed by standard
programs).  Similar 'abort' looks like '-1 throw' to exception handlers.

'ABORT"' ( compilation 'ccc"' -- ; run-time f --  ) core,exception-ext "abort-quote"
   If any bit of f is non-zero, perform the function of '-2 throw',
displaying the string ccc if there is no exception frame on the
exception stack.

'abort' ( ?? -- ??  ) core,exception-ext "abort"
   '-1 throw'.

   For problems that are not that awful that you need to abort
execution, you can just display a warning.  The variable 'warnings'
allows to tune how many warnings you see.

'WARNING"' ( compilation 'ccc"' -- ; run-time f --  ) gforth-1.0 "WARNING""
   if f is non-zero, display the string ccc as warning message.

'warnings' ( -- addr  ) gforth-0.2 "warnings"
   set warnings level to
'0'
     turns warnings off
'-1'
     turns normal warnings on
'-2'
     turns beginner warnings on
'-3'
     pedantic warnings on
'-4'
     turns warnings into errors (including beginner warnings)

6.10 Defining Words
===================

Defining words are used to extend Forth by creating new entries in the
dictionary.

6.10.1 'CREATE'
---------------

Defining words are used to create new entries in the dictionary.  The
simplest defining word is 'CREATE'.  'CREATE' is used like this:

     CREATE new-word1

   'CREATE' is a parsing word, i.e., it takes an argument from the input
stream ('new-word1' in our example).  It generates a dictionary entry
for 'new-word1'.  When 'new-word1' is executed, all that it does is
leave an address on the stack.  The address represents the value of the
data space pointer ('HERE') at the time that 'new-word1' was defined.
Therefore, 'CREATE' is a way of associating a name with the address of a
region of memory.

'Create' ( "name" --  ) core "Create"

   Note that Standard Forth guarantees only for 'create' that its body
is in dictionary data space (i.e., where 'here', 'allot' etc.  work,
*note Dictionary allocation::).  Also, in Standard Forth only 'create'd
words can be modified with 'does>' (*note User-defined Defining
Words::).  And in Standard Forth '>body' can only be applied to
'create'd words.

   By extending this example to reserve some memory in data space, we
end up with something like a variable.  Here are two different ways to
do it:

     CREATE new-word2 1 cells allot  \ reserve 1 cell - initial value undefined
     CREATE new-word3 4 ,            \ reserve 1 cell and initialise it (to 4)

   The variable can be examined and modified using '@' ("fetch") and '!'
("store") like this:

     new-word2 @ .      \ get address, fetch from it and display
     1234 new-word2 !   \ new value, get address, store to it

   A similar mechanism can be used to create arrays.  For example, an
80-character text input buffer:

     CREATE text-buf 80 chars allot

     text-buf 0 chars + c@ \ the 1st character (offset 0)
     text-buf 3 chars + c@ \ the 4th character (offset 3)

   You can build arbitrarily complex data structures by allocating
appropriate areas of memory.  For further discussions of this, and to
learn about some Gforth tools that make it easier, *Note Structures::.

6.10.2 Variables
----------------

The previous section showed how a sequence of commands could be used to
generate a variable.  As a final refinement, the whole code sequence can
be wrapped up in a defining word (pre-empting the subject of the next
section), making it easier to create new variables:

     : myvariableX ( "name" -- a-addr ) CREATE 1 cells allot ;
     : myvariable0 ( "name" -- a-addr ) CREATE 0 , ;

     myvariableX foo \ variable foo starts off with an unknown value
     myvariable0 joe \ whilst joe is initialised to 0

     45 3 * foo !   \ set foo to 135
     1234 joe !     \ set joe to 1234
     3 joe +!       \ increment joe by 3.. to 1237

   Not surprisingly, there is no need to define 'myvariable', since
Forth already has a definition 'Variable'.  Standard Forth does not
guarantee that a 'Variable' is initialised when it is created (i.e., it
may behave like 'myvariableX').  In contrast, Gforth's 'Variable'
initialises the variable to 0 (i.e., it behaves exactly like
'myvariable0').  Forth also provides '2Variable' and 'fvariable' for
double and floating-point variables, respectively -- they are initialised
to 0.  and 0e in Gforth.  If you use a 'Variable' to store a boolean,
you can use 'on' and 'off' to toggle its state.

'Variable' ( "name" --  ) core "Variable"
   Define name and reserve a cell starting at addr.  name run-time: '(
-- addr )'.

'AVariable' ( "name" --  ) gforth-0.2 "AVariable"
   Works like 'variable', but (when used in cross-compiled code) tells
the cross-compiler that the cell stored in the variable is an address.

'2Variable' ( "name" --  ) double "two-variable"

'fvariable' ( "name" --  ) floating "f-variable"

   Finally, for buffers of arbitrary length there is

'buffer:' ( u "name" --  ) core-ext "buffer-colon"
   Define name and reserve u bytes starting at addr.  name run-time: '(
-- addr )'.  Gforth initializes the reserved bytes to 0, but the
standard does not guarantee this.

6.10.3 Constants
----------------

'Constant' allows you to declare a fixed value and refer to it by name.
For example:

     12 Constant INCHES-PER-FOOT
     3E+08 fconstant SPEED-O-LIGHT

   A 'Variable' can be both read and written, so its run-time behaviour
is to supply an address through which its current value can be
manipulated.  In contrast, the value of a 'Constant' cannot be changed
once it has been declared(1) so it's not necessary to supply the address
-- it is more efficient to return the value of the constant directly.
That's exactly what happens; the run-time effect of a constant is to put
its value on the top of the stack (You can find one way of implementing
'Constant' in *note User-defined Defining Words::).

   Forth also provides '2Constant' and 'fconstant' for defining double
and floating-point constants, respectively.

'Constant' ( w "name" --  ) core "Constant"
   Define a constant name with value w.

   name execution: -- w

'AConstant' ( addr "name" --  ) gforth-0.2 "AConstant"
   Like 'constant', but defines a constant for an address (this only
makes a difference in the cross-compiler).

'2Constant' ( w1 w2 "name" --  ) double "two-constant"

'fconstant' ( r "name" --  ) floating "f-constant"

   Constants in Forth behave differently from their equivalents in other
programming languages.  In other languages, a constant (such as an EQU
in assembler or a #define in C) only exists at compile-time; in the
executable program the constant has been translated into an absolute
number and, unless you are using a symbolic debugger, it's impossible to
know what abstract thing that number represents.  In Forth a constant
has an entry in the header space and remains there after the code that
uses it has been defined.  In fact, it must remain in the dictionary
since it has run-time duties to perform.  For example:

     12 Constant INCHES-PER-FOOT
     : FEET-TO-INCHES ( n1 -- n2 ) INCHES-PER-FOOT * ;

   When 'FEET-TO-INCHES' is executed, it will in turn execute the xt
associated with the constant 'INCHES-PER-FOOT'.  If you use 'see' to
decompile the definition of 'FEET-TO-INCHES', you can see that it makes
a call to 'INCHES-PER-FOOT'.  Some Forth compilers attempt to optimise
constants by in-lining them where they are used.  You can force Gforth
to in-line a constant like this:

     : FEET-TO-INCHES ( n1 -- n2 ) [ INCHES-PER-FOOT ] LITERAL * ;

   If you use 'see' to decompile this version of 'FEET-TO-INCHES', you
can see that 'INCHES-PER-FOOT' is no longer present.  To understand how
this works, read *note Interpret/Compile states::, and *note Literals::.

   In-lining constants in this way might improve execution time
fractionally, and can ensure that a constant is now only referenced at
compile-time.  However, the definition of the constant still remains in
the dictionary.  Some Forth compilers provide a mechanism for
controlling a second dictionary for holding transient words such that
this second dictionary can be deleted later in order to recover memory
space.  However, there is no standard way of doing this.

   ---------- Footnotes ----------

   (1) Well, often it can be -- but not in a Standard, portable way.
It's safer to use a 'Value' (read on).

6.10.4 Values
-------------

A 'Value' behaves like a 'Constant', but it can be changed.  'TO' is a
parsing word that changes a 'Values'.  In Gforth (not in Standard Forth)
you can access (and change) a 'value' also with '>body'.

   Here are some examples:

     12 Value APPLES     \ Define APPLES with an initial value of 12
     34 TO APPLES        \ Change the value of APPLES. TO is a parsing word
     1 ' APPLES >body +! \ Increment APPLES.  Non-standard usage.
     APPLES              \ puts 35 on the top of the stack.

'Value' ( w "name" --  ) core-ext "Value"
   Define name with the initial value w; this value can be changed with
'to name' or '->name'.

   name execution: -- w2

'AValue' ( w "name" --  ) gforth-0.6 "AValue"
   Like 'value', but defines a value for an address (this only makes a
difference in the cross-compiler).

'2Value' ( d "name" --  ) double-ext "two-value"

'fvalue' ( r "name" --  ) floating-ext "f-value"
   Define name '( -- r1 )' where r1 initially is r; this value can be
changed with 'to name' or '->name'.

'TO' ( value "name" --  ) core-ext "TO"
   changes the value of NAME to VALUE

'+TO' ( value "name" --  ) gforth-1.0 "+TO"
   increments the value of NAME by VALUE

6.10.5 Varues
-------------

Sometimes you want to take the address of a value-like word.  Because
this has some disadvantages, Gforth asks you to be explicit about it,
and use 'varue' (named that way because it combines characteristics of a
variable and a value) to declare the name.

'Varue' ( w "name" --  ) gforth-1.0 "Varue"
   Like 'value', but you can also use 'addr name'; in the future, varues
may be less efficient than values.

'2varue' ( x1 x2 "name" --  ) gforth-1.0 "2varue"
   Like '2value', but you can also use 'addr name'; in the future,
2varues may be less efficient than 2values.

'fvarue' ( r "name" --  ) gforth-1.0 "fvarue"
   Like 'fvalue', but you can also use 'addr name'; in the future,
fvarues may be less efficient than fvalues.

'addr' ( "name" -- addr  ) gforth-1.0 "addr"
   provides the address ADDR of the varue, 2varue, or fvarue NAME or a
local name defined with one of 'wa: ca: da: fa: xta:'.

6.10.6 Colon Definitions
------------------------

     : name ( ... -- ... )
         word1 word2 word3 ;

Creates a word called 'name' that, upon execution, executes 'word1 word2
word3'.  'name' is a "(colon) definition".

   The explanation above is somewhat superficial.  For simple examples
of colon definitions see *note Your first definition::.  For an in-depth
discussion of some of the issues involved, *Note Interpretation and
Compilation Semantics::.

':' ( "name" -- colon-sys  ) core "colon"

';' ( compilation colon-sys -- ; run-time nest-sys --  ) core "semicolon"

   We plan to to perform automatic inlining eventually, but for now you
can perform inlining with

'inline:' ( "name" -- inline:-sys  ) gforth-experimental "inline-colon"
   Start inline colon definition.  The code between 'inline:' and
';inline' has to compile (not perform) the code to be inlined, but the
resulting definition name is a colon definition that performs the
inlined code.  Note that the compiling code must have the stack effect
'( -- )', otherwise you will get an error when Gforth tries to create
the colon definition for name.

';inline' ( inline:-sys --  ) gforth-experimental "semi-inline"
   end inline definition started with 'inline:'

   As an example, you can define an inlined word and use it with

     inline: my2dup ( a b -- a b a b )
         ]] over over [[ ;inline

     #1. my2dup d. d.
     : foo my2dup ;
     #1. foo d. d.
     see foo

   Inline words are related to macros (*note Macros::); the difference
is that a macro has immediate compilation semantics while an
'inline:'-defined word has default compilation semantics; this means
that you normally use a macro only inside a colon definition, while you
can use an 'inline:' word also interpretively.  But that also means that
you can do some things with macros that you cannot do as an 'inline:'
word.  E.g.,

     \ Doesn't work:
     \   inline: endif ]] then [[ ;inline
     \ Instead, write a macro:
     : endif ]] then [[ ; immediate

   Conversely, for words that would be fine as non-immediate colon
definitions, define them as non-immediate colon definitions or (if
utmost performance is required) as 'inline:' words; don't define them as
macros, because then you cannot properly use them interpretively:

     : another2dup ]] over over [[ ; immediate
     \ Doesn't work:
     \   #1. another2dup d. d.

   You may wonder why you have to write compiling code between 'inline:'
and ';inline'.  That's because the implementation of an inline word like
'my2dup' above works similar to:

     : compile-my2dup ( xt -- )
         drop ]] over over [[ ;

     : my2dup [ 0 compile-my2dup ] ;
     ' compile-my2dup set-optimizer

   The 'DROP' and '0' are there because 'compile-my2dup' is the
implementation of 'compile,' for 'my2dup', and 'compile,' expects an xt
(*note User-defined compile-comma::).

6.10.7 Anonymous Definitions
----------------------------

Sometimes you want to define an "anonymous word"; a word without a name.
You can do this with:

':noname' ( -- xt colon-sys  ) core-ext "colon-no-name"

   This leaves the execution token for the word on the stack after the
closing ';'.  Here's an example in which a deferred word is initialised
with an 'xt' from an anonymous colon definition:

     Defer deferred
     :noname ( ... -- ... )
       ... ;
     IS deferred

Gforth provides an alternative way of doing this, using two separate
words:

'noname' ( --  ) gforth-0.2 "noname"
   The next defined word will be anonymous.  The defining word will
leave the input stream alone.  The xt of the defined word will be given
by 'latestxt'.

'latestxt' ( -- xt  ) gforth-0.6 "latestxt"
   xt is the execution token of the last word defined.

The previous example can be rewritten using 'noname' and 'latestxt':

     Defer deferred
     noname : ( ... -- ... )
       ... ;
     latestxt IS deferred

'noname' works with any defining word, not just ':'.

   'latestxt' also works when the last word was not defined as 'noname'.
It does not work for combined words, though.  It also has the useful
property that is is valid as soon as the header for a definition has
been built.  Thus:

     latestxt . : foo [ latestxt . ] ; ' foo .

prints 3 numbers; the last two are the same.

6.10.8 Quotations
-----------------

A quotation is an anonymous colon definition inside another colon
definition.  Quotations are useful when dealing with words that consume
an execution token, like 'catch' or 'outfile-execute'.  E.g.  consider
the following example of using 'outfile-execute' (*note Redirection::):

     : some-warning ( n -- )
         cr ." warning# " . ;

     : print-some-warning ( n -- )
         ['] some-warning stderr outfile-execute ;

   Here we defined 'some-warning' as a helper word whose xt we could
pass to outfile-execute.  Instead, we can use a quotation to define such
a word anonymously inside 'print-some-warning':

     : print-some-warning ( n -- )
       [: cr ." warning# " . ;] stderr outfile-execute ;

   The quotation is bouded by '[:' and ';]'.  It produces an execution
token at run-time.

'[:' ( compile-time: -- quotation-sys flag colon-sys  ) gforth-1.0 "bracket-colon"
   Starts a quotation

';]' ( compile-time: quotation-sys -- ; run-time: -- xt  ) gforth-1.0 "semi-bracket"
   ends a quotation

6.10.9 Supplying the name of a defined word
-------------------------------------------

By default, a defining word takes the name for the defined word from the
input stream.  Sometimes you want to supply the name from a string.  You
can do this with:

'nextname' ( c-addr u --  ) gforth-0.2 "nextname"
   The next defined word will have the name C-ADDR U; the defining word
will leave the input stream alone.

   For example:

     s" foo" nextname create

is equivalent to:

     create foo

'nextname' works with any defining word.

6.10.10 User-defined Defining Words
-----------------------------------

You can define new defining words in terms of any existing defining
word, but ':' and 'create'...'does>'/'set-does>' are particularly
flexible, whereas the children of, e.g., 'constant' are all just
constants.

6.10.10.1 User-defined defining words with colon definitions
............................................................

You can create a new defining word by wrapping defining-time code around
an existing defining word and putting the sequence in a colon
definition.

   For example, suppose that you have a word 'stats' that gathers
statistics about colon definitions given the xt of the definition, and
you want every colon definition in your application to make a call to
'stats'.  You can define and use a new version of ':' like this:

     : stats
       ( xt -- ) DUP ." (Gathering statistics for " . ." )"
       ... ;  \ other code

     : my: : latestxt postpone literal ['] stats compile, ;

     my: foo + - ;

   When 'foo' is defined using 'my:' these steps occur:

   * 'my:' is executed.
   * The ':' within the definition (the one between 'my:' and
     'latestxt') is executed, and does just what it always does; it
     parses the input stream for a name, builds a dictionary header for
     the name 'foo' and switches 'state' from interpret to compile.
   * The word 'latestxt' is executed.  It puts the xt for the word that
     is being defined -- 'foo' -- onto the stack.
   * The code that was produced by 'postpone literal' is executed; this
     causes the value on the stack to be compiled as a literal in the
     code area of 'foo'.
   * The code '['] stats' compiles a literal into the definition of
     'my:'.  When 'compile,' is executed, that literal -- the execution
     token for 'stats' -- is layed down in the code area of 'foo' ,
     following the literal(1).
   * At this point, the execution of 'my:' is complete, and control
     returns to the text interpreter.  The text interpreter is in
     compile state, so subsequent text '+ -' is compiled into the
     definition of 'foo' and the ';' terminates the definition as
     always.

   You can use 'see' to decompile a word that was defined using 'my:'
and see how it is different from a normal ':' definition.  For example:

     : bar + - ;  \ like foo but using : rather than my:
     see bar
     : bar
       + - ;
     see foo
     : foo
       `foo stats + - ;

   '`foo' is another way of writing '['] foo'.

   ---------- Footnotes ----------

   (1) Strictly speaking, the mechanism that 'compile,' uses to convert
an xt into something in the code area is implementation-dependent.  A
threaded implementation might spit out the execution token directly
whilst another implementation might spit out a native code sequence.

6.10.10.2 User-defined defining words using create
..................................................

If you want the words defined with your defining words to behave
differently from words defined with standard defining words, you can
write your defining word like this:

     : def-word ( "name" -- )
         CREATE code1
     DOES> ( ... -- ... )
         code2 ;

     def-word name

   This fragment defines a "defining word" 'def-word' and then executes
it.  When 'def-word' executes, it 'CREATE's a new word 'name', and
executes the code code1.  The code code2 is not executed at this time.
The word 'name' is sometimes called a "child" of 'def-word'.

   When you execute 'name', the address of the body of 'name' is put on
the data stack and code2 is executed (the address of the body of 'name'
is the address 'HERE' returns immediately after the 'CREATE', i.e., the
address a 'create'd word returns by default).

   You can use 'def-word' to define a set of child words that behave
similarly; they all have a common run-time behaviour determined by
code2.  Typically, the code1 sequence builds a data area in the body of
the child word.  The structure of the data is common to all children of
'def-word', but the data values are specific -- and private -- to each
child word.  When a child word is executed, the address of its private
data area is passed as a parameter on TOS to be used and manipulated(1)
by code2.

   The two fragments of code that make up the defining words act (are
executed) at two completely separate times:

   * At define time, the defining word executes code1 to generate a
     child word
   * At child execution time, when a child word is invoked, code2 is
     executed, using parameters (data) that are private and specific to
     the child word.

   Another way of understanding the behaviour of 'def-word' and 'name'
is to say that, if you make the following definitions:
     : def-word1 ( "name" -- )
         CREATE code1 ;

     : action1 ( ... -- ... )
         code2 ;

     def-word1 name1

Then using 'name1 action1' is equivalent to using 'name'.

   Another way of writing 'def-word' is (*note Quotations::):

     : def-word ( "name" -- ; name execution: ... -- ... )
         create code1
         [: code2 ;] set-does> ;

   Gforth actually compiles the code using 'does>' into code equivalent
to the latter code.  An advantage of the 'set-does>' approach is that
you can put other code behind it and you can use it inside control
structures without needing workarounds.  A disadvantage is that it is
Gforth-specific.

   A classic example is that you can define 'CONSTANT' in this way:

     : CONSTANT ( w "name" -- )
         CREATE ,
     DOES> ( -- w )
         @ ;

or equivalently

     : CONSTANT ( w "name" -- ; name execution: -- w )
         create ,
         ['] @ set-does> ;

   When you create a constant with '5 CONSTANT five', a set of
define-time actions take place; first a new word 'five' is created, then
the value 5 is laid down in the body of 'five' with ','.  When 'five' is
executed, the address of the body is put on the stack, and '@' retrieves
the value 5.  The word 'five' has no code of its own; it simply contains
a data field and the xt of the quotation or of '@'.

   The final example in this section is intended to remind you that
space reserved in 'CREATE'd words is data space and therefore can be
both read and written by a Standard program(2):

     : foo ( "name" -- )
         CREATE -1 ,
     DOES> ( -- )
         @ . ;

     foo first-word
     foo second-word

     123 ' first-word >BODY !

   If 'first-word' had been a 'CREATE'd word, we could simply have
executed it to get the address of its data field.  However, since it was
defined to have 'DOES>' actions, its execution semantics are to perform
those 'DOES>' actions.  To get the address of its data field it's
necessary to use ''' to get its xt, then '>BODY' to translate the xt
into the address of the data field.  When you execute 'first-word', it
will display '123'.  When you execute 'second-word' it will display
'-1'.

   In the examples above the stack comment after the 'DOES>' specifies
the stack effect of the defined words, not the stack effect of the
following code (the following code expects the address of the body on
the top of stack, which is not reflected in the stack comment).  This is
the convention that I use and recommend (it clashes a bit with using
locals declarations for stack effect specification, though).

   ---------- Footnotes ----------

   (1) It is legitimate both to read and write to this data area.

   (2) Exercise: use this example as a starting point for your own
implementation of 'Value' and 'TO' -- if you get stuck, investigate the
behaviour of ''' and '[']'.

6.10.10.3 Applications of 'CREATE..DOES>'
.........................................

You may wonder how to use this feature.  Here are some usage patterns:

   When you see a sequence of code occurring several times, and you can
identify a meaning, you will factor it out as a colon definition.  When
you see similar colon definitions, you can factor them using
'CREATE..DOES>'.  E.g., an assembler usually defines several words that
look very similar:
     : ori, ( reg-target reg-source n -- )
         0 asm-reg-reg-imm ;
     : andi, ( reg-target reg-source n -- )
         1 asm-reg-reg-imm ;

This could be factored with:
     : reg-reg-imm ( op-code -- )
         CREATE ,
     DOES> ( reg-target reg-source n -- )
         @ asm-reg-reg-imm ;

     0 reg-reg-imm ori,
     1 reg-reg-imm andi,

   Another view of 'CREATE..DOES>' is to consider it as a crude way to
supply a part of the parameters for a word (known as "currying" in the
functional language community).  E.g., '+' needs two parameters.
Creating versions of '+' with one parameter fixed can be done like this:

     : curry+ ( n1 "name" -- )
         CREATE ,
     DOES> ( n2 -- n1+n2 )
         @ + ;

      3 curry+ 3+
     -2 curry+ 2-

6.10.10.4 The gory details of 'CREATE..DOES>'
.............................................

'DOES>' ( compilation colon-sys1 -- colon-sys2  ) core "does"

   This means that you need not use 'CREATE' and 'DOES>' in the same
definition; you can put the 'DOES>'-part in a separate definition.  This
allows us to, e.g., select among different 'DOES>'-parts:
     : does1
     DOES> ( ... -- ... )
         code1 ;

     : does2
     DOES> ( ... -- ... )
         code2 ;

     : def-word ( ... -- ... )
         create ...
         IF
            does1
         ELSE
            does2
         ENDIF ;

   In this example, the selection of whether to use 'does1' or 'does2'
is made at definition-time; at the time that the child word is
'CREATE'd.

   Note that the property of 'does>' to end the definition makes it
necessary to introduce extra definitions 'does1' and 'does2'.  You can
avoid that with 'set-does>':

     : def-word ( ... -- ... )
         create ...
         IF
            [: code1 ;] set-does>
         ELSE
            [: code2 ;] set-does>
         ENDIF ;

   In a standard program you can apply a 'DOES>'-part only if the last
word was defined with 'CREATE'.  In Gforth, the 'DOES>'-part will
override the behaviour of the last word defined in any case.  In a
standard program, you can use 'DOES>' only in a colon definition.  In
Gforth, you can also use it in interpretation state, in a kind of
one-shot mode; for example:
     CREATE name ( ... -- ... )
       initialization
     DOES>
       code ;

is equivalent to the standard:
     :noname
     DOES>
         code ;
     CREATE name EXECUTE ( ... -- ... )
         initialization

   Gforth also supports quotations in interpreted code, and quotations
save and restore the current definition, so you can also write the
example above also as:

     CREATE name ( ... -- ... )
       initialization
     [: code ;] set-does>

'set-does>' ( xt --  ) gforth-1.0 "set-does>"
   Changes the current word such that it pushes its body address and
then executes xt.  Also changes the 'compile,' implementation
accordingly.  Call 'set-optimizer' afterwards if you want a more
efficient implementation.

'>body' ( xt -- a_addr  ) core "to-body"
   Get the address of the body of the word represented by xt (the
address of the word's data field).

6.10.10.5 Advanced does> usage example
......................................

The MIPS disassembler ('arch/mips/disasm.fs') contains many words for
disassembling instructions, that follow a very repetetive scheme:

     :noname DISASM-OPERANDS s" INST-NAME" type ;
     ENTRY-NUM cells TABLE + !

   Of course, this inspires the idea to factor out the commonalities to
allow a definition like

     DISASM-OPERANDS ENTRY-NUM TABLE define-inst INST-NAME

   The parameters DISASM-OPERANDS and TABLE are usually correlated.
Moreover, before I wrote the disassembler, there already existed code
that defines instructions like this:

     ENTRY-NUM INST-FORMAT INST-NAME

   This code comes from the assembler and resides in
'arch/mips/insts.fs'.

   So I had to define the INST-FORMAT words that performed the scheme
above when executed.  At first I chose to use run-time code-generation:

     : INST-FORMAT ( entry-num "name" -- ; compiled code: addr w -- )
       :noname Postpone DISASM-OPERANDS
       name Postpone sliteral Postpone type Postpone ;
       swap cells TABLE + ! ;

   Note that this supplies the other two parameters of the scheme above.

   An alternative would have been to write this using 'create'/'does>':

     : INST-FORMAT ( entry-num "name" -- )
       here name string, ( entry-num c-addr ) \ parse and save "name"
       noname create , ( entry-num )
       latestxt swap cells TABLE + !
     does> ( addr w -- )
       \ disassemble instruction w at addr
       @ >r
       DISASM-OPERANDS
       r> count type ;

   Somehow the first solution is simpler, mainly because it's simpler to
shift a string from definition-time to use-time with 'sliteral' than
with 'string,' and friends.

   I wrote a lot of words following this scheme and soon thought about
factoring out the commonalities among them.  Note that this uses a
two-level defining word, i.e., a word that defines ordinary defining
words.

   This time a solution involving 'postpone' and friends seemed more
difficult (try it as an exercise), so I decided to use a
'create'/'does>' word; since I was already at it, I also used
'create'/'does>' for the lower level (try using 'postpone' etc.  as an
exercise), resulting in the following definition:

     : define-format ( disasm-xt table-xt -- )
         \ define an instruction format that uses disasm-xt for
         \ disassembling and enters the defined instructions into table
         \ table-xt
         create 2,
     does> ( u "inst" -- )
         \ defines an anonymous word for disassembling instruction inst,
         \ and enters it as u-th entry into table-xt
         2@ swap here name string, ( u table-xt disasm-xt c-addr ) \ remember string
         noname create 2,      \ define anonymous word
         execute latestxt swap ! \ enter xt of defined word into table-xt
     does> ( addr w -- )
         \ disassemble instruction w at addr
         2@ >r ( addr w disasm-xt R: c-addr )
         execute ( R: c-addr ) \ disassemble operands
         r> count type ; \ print name

   Note that the tables here (in contrast to above) do the 'cells +' by
themselves (that's why you have to pass an xt).  This word is used in
the following way:

     ' DISASM-OPERANDS ' TABLE define-format INST-FORMAT

   As shown above, the defined instruction format is then used like
this:

     ENTRY-NUM INST-FORMAT INST-NAME

   In terms of currying, this kind of two-level defining word provides
the parameters in three stages: first DISASM-OPERANDS and TABLE, then
ENTRY-NUM and INST-NAME, finally 'addr w', i.e., the instruction to be
disassembled.

   Of course this did not quite fit all the instruction format names
used in 'insts.fs', so I had to define a few wrappers that conditioned
the parameters into the right form.

   If you have trouble following this section, don't worry.  First, this
is involved and takes time (and probably some playing around) to
understand; second, this is the first two-level 'create'/'does>' word I
have written in seventeen years of Forth; and if I did not have
'insts.fs' to start with, I may well have elected to use just a
one-level defining word (with some repeating of parameters when using
the defining word).  So it is not necessary to understand this, but it
may improve your understanding of Forth.

6.10.10.6 User-defined 'to' and 'defer@'
........................................

Gforth's values have several operators: 'to' (to which 'is' is an alias,
and 'defer!' takes an xt instead of a name in the input stream), '+to',
'addr', and 'action-of' (where 'defer@' takes an xt instead of a name in
the input stream).

   Gforth allows you to change the '(to)' action of a word.

'(to)' ( val operation xt --  ) gforth-1.0 "paren-to"
   xt is of a value like word name.  Stores val 'to' name.  operation
selects between 'to', '+to', 'addr', and 'action-of'.

'to-table:' ( "name" "xt1" .. "xtn" --  ) gforth-experimental "to-table-colon"
   create a table with entries for 'TO', '+TO', 'ADDR', and 'ACTION-OF'.
Use 'n/a' to mark unsupported operations.

'to-method:' ( xt table "name" --  ) gforth-experimental "to-method-colon"
   create a to-method, where XT computes the address to access the
field, and TABLE contains the operators to store to it.

'set-to' ( to-xt --  ) gforth-1.0 "set-to"
   Sets the implementation of the '(to) ( val xt -- )' method of the
current word to to-xt.

'n/a' ( --  ) gforth-experimental "not-available"
   this word can be ticked, but throws an "Operation not supported"
exception on interpretation and compilation.  Use this for methods and
alike that aren't supported.

   '(to)' is a word used inside 'to': it stores the value at run-time.
The general stack effect of '(to)' method is '( val operation xt -- )',
where xt identifies the word stored into, operation the actual variant
of 'to'-like operations, and val is the value (of appropriate type)
stored there.

   You shall implement the 'to'-method using 'to-table:' to create a
type-specific table of operations (not specified slots at the end of the
table are filled up with 'n/a'), and using 'to-method:' together with
the operation to get from the xt of the value to its data field (usually
'>body' for values in the dictionary, but value-style data can also
reside in structures or user areas).

   E.g., one can implement 'fvalue' as follows:

     to-table: f!-table f! f+!
     ' >body f!-table to-method: fvalue-to

     : fvalue ( r "name" -- ; name: -- r )
       create f,
       ['] f@ set-does>
       ['] fvalue-to set-to ;

     5e fvalue foo
     : bar foo 1e f+ to foo ;
     see bar

6.10.10.7 User-defined 'compile,'
.................................

You can also change the implementation of 'compile,' for a word, with

'set-optimizer' ( xt --  ) gforth-1.0 "set-optimizer"
   Changes the current word such that 'compile,'ing it executes xt (with
the same stack contents as passed to 'compile,').  Note that 'compile,'
must be consistent with 'execute', so you must use 'set-optimizer' only
to install a more efficient implementation of the same behaviour.

'opt:' ( compilation -- colon-sys2 ; run-time -- nest-sys  ) gforth-1.0 "opt:"
   Starts a nameless colon definition; when it is complete, this colon
definition will become the 'compile,' implementation of the latest word
(before the 'opt:').

   Note that the resulting 'compile,' must still be equivalent to
'postpone literal postpone execute', so 'set-optimizer' is useful for
efficiency, not for changing the behaviour.  There is nothing that
prevents you from shooting yourself in the foot, however.  You can check
whether your uses of 'set-optimizer' are correct by comparing the
results when you use it with the results you get when you disable your
uses by first defining

     : set-optimizer drop ;

   As an example of the use of 'set-optimizer', we can enhance one of
the definitions of 'CONSTANT' above as follows.

     : CONSTANT ( n "name" -- ; name: -- n )
       create ,
       ['] @ set-does>
       [: >body @ postpone literal ;] set-optimizer
     ;

   The only change is the addition of the 'set-optimizer' line.  When
you define a constant and compile it:

     5 constant five
     : foo five ;

   the compiled 'five' in 'foo' is now compiled to the literal 5 instead
of a generic invocation of 'five'.  The quotation has the same stack
effect as 'compile,': '( xt -- )'.  The passed xt belongs to the
'compile,'d word, i.e., 'five' in the example.  In the example the xt is
first converted to the body address, then the value 5 at that place is
fetched, and that value is compiled with the 'postpone literal' (*note
Literals::).

   This use of 'set-optimizer' assumes that the user does not change the
value of a constant with, e.g., '6 ' five >body !'.  While 'five' has
been defined with 'create', that is an implementation detail of
'CONSTANT', and if you don't document it, the user must not rely on it.
And if you use 'set-optimizer' in a way that assumes that the body does
not change (like is done here), you must not document that 'create' is
used; and conversely, if you document it, you have to write the
'compile,' implementation such that it can deal with changing bodies.

   Another example is a better-optimized variant of the 'fvalue' example
above:

     : compile-fvalue-to ( xt-value-to -- )
       drop ]] >body f! [[ ;

     : fvalue-to ( r xt -- )
       >body f! ;
     ' compile-fvalue-to set-optimizer

     : fvalue ( r "name" -- ; name: -- r )
       create f,
       ['] f@ set-does>
       [: >body ]] literal f@ [[ ;] set-optimizer
       ['] fvalue-to set-to ;

     5e fvalue foo
     : bar foo 1e f+ to foo ;
     see bar

   Compare the code for 'bar' with the one for the earlier definition.
Here we see the optimization of both the code for reading the fvalue
(coming from the 'set-optimizer' in 'fvalue') and for writing the fvalue
(coming from the 'set-optimizer' applied to 'fvalue-to'.  Because an
fvalue can change (unlike a constant), the reading part (inside
'fvalue') compiles the address and a 'f@' that is performed at run-time.

   For 'fvalue-to', the 'compile,' implementation basically just
compiles the code executed by 'fvalue' inline.  The compilation
semantics of 'to' compiles the address as literal and then the '(to)'
implementation (i.e., 'fvalue-to').  In this process the '>body' is
optimized away.

   In practice Gforth's 'fvalue' includes a few additional twists, e.g.,
to support '+TO'.

   Note that the call to 'set-optimizer' has to be performed after the
call to 'set-does>' (or 'does>', because 'set-does>' overwrites the
'compile,' implementation itself.

   As we can see in the 'fvalue-to' example, we can also apply
'set-optimizer' to individual words rather than inside a defining word
like 'constant' or 'fvalue'.  In this case, the xt of the word passed to
optimizer is usually unnecessary and is 'drop'ped, as in
'compile-fvalue-to'.

   The engine 'gforth-itc' uses ',' for 'compile,' and 'set-optimizer'
has no effect there.

6.10.10.8 Creating from a prototype
...................................

In the above we show how to define a word by first using 'create', and
then modifying it with 'set-does>', 'set-to', 'set-optimizer' etc.

   An alternative way is to create a prototype using these words, and
then create a new word from that prototype.  This kind of copying does
not cover the body, so that has to be allocated and initialized
explicitly.  Taking 'fvalue' above, we could instead define it as:

     create fvalue-prototype ( -- r )
     ['] f@ set-does>
     [: >body ]] literal f@ [[ ;] set-optimizer
     ['] fvalue-to set-to

     : fvalue ( r "name" -- ; name: -- r )
       ``fvalue-prototype create-from f, reveal ;

   An advantage of this approach is that creating 'fvalue' words is now
faster, because it does not need to first duplicate the header methods
of 'create', modify them, and eventually deduplicate them.  But this
advantage is only relevant if the number of words created with this
defining word is huge.

'create-from' ( nt "name" --  ) gforth-1.0 "create-from"
   Create a word name that behaves like nt, but with an empty body.  nt
must be the nt of a named word.  The resulting header is not yet
revealed.  Creating a word with 'create-from' without using any 'set-'
words is faster than if you create a word using 'set-' words,
'immediate', or 'does>'.  You can use 'noname' with 'create-from'.

'reveal' ( --  ) gforth-0.2 "reveal"
   Put the current word in the wordlist current at the time of the
header definition.

   The performance advantage does not extend to using 'noname' with the
defining word.  Therefore we also have

'noname-from' ( xt --  ) gforth-1.0 "noname-from"
   Create a nameless word that behaves like xt, but with an empty body.
xt must be the nt of a nameless word.

   Here's a usage example:

     ``fvalue-prototype noname create-from
     latestnt constant noname-fvalue-prototype

     : noname-fvalue ( r -- xt ; xt execution: -- r )
       noname-fvalue-prototype noname-from f,
       latestxt ;

6.10.10.9 Making a word current
...............................

Many words mentioned above, such as 'immediate' or 'set-optimizer'
change the "current" or "most recently defined" word.  Sometimes you
want to change an earlier word.  You can do this with

'make-latest' ( nt --  ) gforth-1.0 "make-latest"
   Make nt the latest definition, which can be manipulated by
'immediate' and 'set-*' operations.  If you have used (especially
compiled) the word referred to by nt already, do not change the
behaviour of the word (only its implementation), otherwise you may get a
surprising mix of behaviours that is not consistent between Gforth
engines and versions.

6.10.10.10 'Const-does>'
........................

A frequent use of 'create'...'does>' is for transferring some values
from definition-time to run-time.  Gforth supports this use with

'const-does>' ( run-time: w*uw r*ur uw ur "name" --  ) gforth-obsolete "const-does"
   Defines NAME and returns.

   NAME execution: pushes W*UW R*UR, then performs the code following
the 'const-does>'.

   A typical use of this word is:

     : curry+ ( n1 "name" -- )
     1 0 CONST-DOES> ( n2 -- n1+n2 )
         + ;

     3 curry+ 3+

   Here the '1 0' means that 1 cell and 0 floats are transferred from
definition to run-time.

   The advantages of using 'const-does>' are:

   * You don't have to deal with storing and retrieving the values,
     i.e., your program becomes more writable and readable.

   * When using 'does>', you have to introduce a '@' that cannot be
     optimized away (because you could change the data using
     '>body'...'!'); 'const-does>' avoids this problem.

   A Standard Forth implementation of 'const-does>' is available in
'compat/const-does.fs'.

6.10.11 Deferred Words
----------------------

The defining word 'Defer' allows you to define a word by name without
defining its behaviour; the definition of its behaviour is deferred.
Here are two situation where this can be useful:

   * Where you want to allow the behaviour of a word to be altered
     later, and for all precompiled references to the word to change
     when its behaviour is changed.
   * For mutual recursion; *Note Calls and returns::.

   In the following example, 'foo' always invokes the version of 'greet'
that prints "'Good morning'" whilst 'bar' always invokes the version
that prints "'Hello'".  There is no way of getting 'foo' to use the
later version without re-ordering the source code and recompiling it.

     : greet ." Good morning" ;
     : foo ... greet ... ;
     : greet ." Hello" ;
     : bar ... greet ... ;

   This problem can be solved by defining 'greet' as a 'Defer'red word.
The behaviour of a 'Defer'red word can be defined and redefined at any
time by using 'IS' to associate the xt of a previously-defined word with
it.  The previous example becomes:

     Defer greet ( -- )
     : foo ... greet ... ;
     : bar ... greet ... ;
     : greet1 ( -- ) ." Good morning" ;
     : greet2 ( -- ) ." Hello" ;
     ' greet2 IS greet  \ make greet behave like greet2

   Programming style note:

   You should write a stack comment for every deferred word, and put
only XTs into deferred words that conform to this stack effect.
Otherwise it's too difficult to use the deferred word.

   A deferred word can be used to improve the statistics-gathering
example from *note User-defined Defining Words::; rather than edit the
application's source code to change every ':' to a 'my:', do this:

     : real: : ;     \ retain access to the original
     defer :         \ redefine as a deferred word
     ' my: IS :      \ use special version of :
     \
     \ load application here
     \
     ' real: IS :    \ go back to the original

   One thing to note is that 'IS' has special compilation semantics,
such that it parses the name at compile time (like 'TO'):

     : set-greet ( xt -- )
       IS greet ;

     ' greet1 set-greet

   In situations where 'IS' does not fit, use 'defer!' instead.

   A deferred word can only inherit execution semantics from the xt
(because that is all that an xt can represent -- for more discussion of
this *note Tokens for Words::); by default it will have default
interpretation and compilation semantics deriving from this execution
semantics.  However, you can change the interpretation and compilation
semantics of the deferred word in the usual ways:

     : bar .... ; immediate
     Defer fred immediate
     Defer jim

     ' bar IS jim  \ jim has default semantics
     ' bar IS fred \ fred is immediate

'Defer' ( "name" --  ) core-ext "Defer"
   Define a deferred word name; its execution semantics can be set with
'defer!' or 'is' (and they have to, before first executing name.

'defer!' ( xt xt-deferred --  ) core-ext "defer-store"
   Changes the 'defer'red word XT-DEFERRED to execute XT.

'IS' ( value "name" --  ) core-ext "IS"
   changes the 'defer'red word NAME to execute VALUE

'defer@' ( xt-deferred -- xt  ) core-ext "new-defer-fetch"
   xt represents the word currently associated with the deferred word
xt-deferred.

'action-of' ( interpretation "name" -- xt; compilation "name" -- ; run-time -- xt  ) core-ext "action-of"
   Xt is the XT that is currently assigned to name.

   Definitions of these Forth-2012 words in Forth-94 are provided in
'compat/defer.fs'.  In addition, Gforth provides:

'defers' ( compilation "name" -- ; run-time ... -- ...  ) gforth-0.2 "defers"
   Compiles the present contents of the deferred word name into the
current definition.  I.e., this produces static binding as if name was
not deferred.

'wrap-xt' ( xt1 xt2 xt: xt3 -- ...  ) gforth-1.0 "wrap-xt"
   Set deferred word xt2 to xt1 and execute xt3.  Restore afterwards.

'preserve' ( "name" --  ) gforth-1.0 "preserve"
   emit code that reverts a deferred word to the state at compilation

6.10.12 Forward
---------------

The defining word 'Forward' in 'forward.fs' allows you to create forward
references, which are resolved automatically, and do not incur
additional costs like the indirection of 'Defer'.  However, these
forward definitions only work for colon definitions.

'forward' ( "name" --  ) gforth-1.0 "forward"
   Defines a forward reference to a colon definition.  Defining a colon
definition with the same name in the same wordlist resolves the forward
references.  Use '.unresolved' to check whether any forwards are
unresolved.

'.unresolved' ( --  ) gforth-1.0 ".unresolved"
   print all unresolved forward references

6.10.13 Aliases
---------------

The defining word 'synonym' allows you to define a word by name that has
the same behaviour as some other word.  Here are two situation where
this can be useful:

   * When you want access to a word's definition from a different word
     list (for an example of this, see the definition of the 'Root' word
     list in the Gforth source).
   * When you want to create a synonym; a definition that can be known
     by either of two names (for example, 'THEN' and 'ENDIF' are
     synonyms).

'Synonym' ( "name" "oldname" --  ) tools-ext "Synonym"
   Define name to behave the same way as oldname: Same interpretation
semantics, same compilation semantics, same 'to'/'defer!' and 'defer@'
semantics.

   Gforth also offers the non-standard 'alias', that does not inherit
the compilation semantics, 'to'/'defer!' or 'defer@' semantics from its
parent.  You can then change, e.g., the compilation semantics with,
e.g., 'immediate'.

'Alias' ( xt "name" --  ) gforth-0.2 "Alias"
   Define name as a word that performs xt.  Unlike for deferred words,
aliases don't have an indirection overhead when compiled.

   Example:

     : foo ... ; immediate

     ' foo Alias bar1           \ bar1 is not an immediate word
     ' foo Alias bar2 immediate \ bar2 is an immediate word
     synonym bar3 foo           \ bar3 is an immediate word

   Both synonyms and aliases have a different nt than the original, but
ticking it (or using 'name>interpret') produces the same xt as the
original (*note Tokens for Words::).

6.11 Interpretation and Compilation Semantics
=============================================

The "interpretation semantics" of a (named) word are what the text
interpreter does when it encounters the word in interpret state.  It
also appears in some other contexts, e.g., the execution token returned
by '' word' identifies the interpretation semantics of word (in other
words, '' word execute' is equivalent to interpret-state text
interpretation of 'word').

   The "compilation semantics" of a (named) word are what the text
interpreter does when it encounters the word in compile state.  It also
appears in other contexts, e.g, 'POSTPONE word' compiles(1) the
compilation semantics of word.

   Most words have default compilation semantics: compile the execution
semantics (stack effect '( -- )').  But a number of words have other
compilation semantics, documented for the individual word (including its
stack effect).

   The standard also talks about "execution semantics".  In the standard
it never differs from the interpretation semantics if both are defined,
but one or both of them may not be defined.  Gforth makes no difference
between interpretation and execution semantics, so these terms are used
interchangeably.

   In Gforth (since 1.0) all words have defined interpretation/execution
semantics.  For many words that have no defined interpretation nor
execution semantics in the standard (e.g., 'if'), the
interpretation/execution semantics in Gforth are to perform the
compilation semantics.

   In the standard, execution semantics are used to define
interpretation and compilation semantics by default: By default, the
interpretation semantics of a word are to 'execute' its execution
semantics, and the compilation semantics of a word are to 'compile,' its
execution semantics.(2)

   Unnamed words (*note Anonymous Definitions::) cannot be encountered
by the text interpreter, ticked, or 'postpone'd.  Such a word is
represented by its xt (*note Tokens for Words::), and the behaviour when
this xt is 'execute'd is called its execution semantics.

   You can change the semantics of the most-recently defined word:

'immediate' ( --  ) core "immediate"
   Make the compilation semantics of a word be to 'execute' the
execution semantics.

'compile-only' ( --  ) gforth-0.2 "compile-only"
   Mark the last definition as compile-only; as a result, the text
interpreter and ''' will warn when they encounter such a word.

'restrict' ( --  ) gforth-0.2 "restrict"
   A synonym for 'compile-only'

   By convention, words with non-default compilation semantics (e.g.,
immediate words) often have names surrounded with brackets (e.g., '[']',
*note Execution token::).

   Note that ticking (''') a compile-only word gives a warning ("<word>
is compile-only").

   ---------- Footnotes ----------

   (1) In standard terminology, "appends to the current definition".

   (2) In standard terminology: The default interpretation semantics are
its execution semantics; the default compilation semantics are to append
its execution semantics to the execution semantics of the current
definition.

6.11.1 Combined Words
---------------------

Gforth allows you to define "combined words" -- words that have an
arbitrary combination of interpretation and compilation semantics.

'interpret/compile:' ( interp-xt comp-xt "name" --  ) gforth-0.2 "interpret/compile:"

   This feature was introduced for implementing 'TO' and 'S"'.  I
recommend that you do not define such words, as cute as they may be:
they make it hard to get at both parts of the word in some contexts.
E.g., assume you want to get an execution token for the compilation
part.  Instead, define two words, one that embodies the interpretation
part, and one that embodies the compilation part.  Once you have done
that, you can define a combined word with 'interpret/compile:' for the
convenience of your users.

   You might try to use this feature to provide an optimizing
implementation of the default compilation semantics of a word.  For
example, by defining:
     :noname
        foo bar ;
     :noname
        POSTPONE foo POSTPONE bar ;
     interpret/compile: opti-foobar

as an optimizing version of:

     : foobar
         foo bar ;

   Unfortunately, this does not work correctly with '[compile]', because
'[compile]' assumes that the compilation semantics of all
'interpret/compile:' words are non-default.  I.e., '[compile]
opti-foobar' would compile compilation semantics, whereas '[compile]
foobar' would compile interpretation semantics.

   Some people try to use "state-smart" words to emulate the feature
provided by 'interpret/compile:' (words are state-smart if they check
'STATE' during execution).  E.g., they would try to code 'foobar' like
this:

     : foobar
       STATE @
       IF ( compilation state )
         POSTPONE foo POSTPONE bar
       ELSE
         foo bar
       ENDIF ; immediate

   Although this works if 'foobar' is only processed by the text
interpreter, it does not work in other contexts (like ''' or
'POSTPONE').  E.g., '' foobar' will produce an execution token for a
state-smart word, not for the interpretation semantics of the original
'foobar'; when you execute this execution token (directly with 'EXECUTE'
or indirectly through 'COMPILE,') in compile state, the result will not
be what you expected (i.e., it will not perform 'foo bar').  State-smart
words are a bad idea.  Simply don't write them(1)!

   ---------- Footnotes ----------

   (1) For a more detailed discussion of this topic, see M. Anton Ertl,
''State'-smartness---Why it is Evil and How to Exorcise it
(https://www.complang.tuwien.ac.at/papers/ertl98.ps.gz)', EuroForth '98.

6.12 Tokens for Words
=====================

This section describes the creation and use of tokens that represent
words.

6.12.1 Execution token
----------------------

An "execution token" (_xt_) represents some behaviour of a word.  You
can use 'execute' to invoke the behaviour represented by the xt and
'compile,' (*note Macros::) to compile it into the current definition.
Other uses include deferred words (*note Deferred Words::).

   In particular, there is _the_ execution token of a word that
represents its interpretation semantics aka execution semantics.(1)

   For a named word x, you can use '`x' to get its execution token:

     5 `. ( n xt )
     execute ( )      \ execute the xt (i.e., ".")
     : foo `. execute ;
     5 foo

   However, the '`' prefix is a Gforth extension, so you may prefer to
use the standard Forth words:

''' ( "name" -- xt  ) core "tick"
   xt represents name's interpretation semantics.  Perform '-14 throw'
if the word has no interpretation semantics.

'[']' ( compilation. "name" -- ; run-time. -- xt  ) core "bracket-tick"
   xt represents name's interpretation semantics.  Perform '-14 throw'
if the word has no interpretation semantics.

   These are parsing words (whereas '`x' is treated as a literal by a
recognizer), and you may find the behaviour in interpreted and compiled
code unintuitive:

     5 ' .   ( n xt )
     execute ( )      \ execute the xt of .
     \ does not work as intended:
     \ : foo ' . ;
     \ 5 foo execute
     \ instead:
     : foo ['] . ;
     5 foo execute    \ execute the xt of .
     \ Usage of ' in colon definition:
     : bar ' execute ;
     5 bar .          \ execute the xt of .

   ''' parses at run-time, so if you put it in a colon definition, as in
'bar', it does not consume the next word in the colon definition, but
the next word at run-time (i.e., the '.' in the invocation of 'bar').
If you want to put a literal xt in a colon definition without writing
'`x', write '['] x'.

   Gforth's '`x', ''' and '[']' warn when you use them on compile-only
words, because such usage may be non-portable between different Forth
systems.

   You can avoid that warning as well as the portability problems by
defining an immediate variant of the word, e.g.:

     : if postpone if ; immediate
     : test [ ' if execute ] ." test" then ;

   The resulting execution token performs the compilation semantics of
'if' when 'execute'd.

   Another way to get an xt is ':noname' or 'latestxt' (*note Anonymous
Definitions::).  For anonymous words this gives an xt for the only
behaviour the word has (the execution semantics), but you can also use
it after defining a named word to get its xt.

     :noname ." hello" ;
     execute

   An xt occupies one cell and can be manipulated like any other cell.

   In Standard Forth the xt is just an abstract data type (i.e., defined
by the operations that produce or consume it).  The concrete
implementation (since Gforth 1.0) is the body address (for old hands:
PFA) of the word; in Gforth 0.7 and earlier, the xt was implemented as
code field addres (CFA, 2 cells before the PFA).

'execute' ( xt -- ) core "execute"
   Perform the semantics represented by the execution token, xt.

'execute-exit' ( compilation -- ; run-time xt nest-sys --  ) gforth-1.0 "execute-exit"
   Execute 'xt' and return from the current definition, in a
tail-call-optimized way: The return address 'nest-sys' and the locals
are deallocated before executing 'xt'.

'perform' ( a-addr -- ) gforth-0.2 "perform"
   '@ execute'.

   'Noop' is sometimes used to have a placeholder execution token:

'noop' ( -- ) gforth-0.2 "noop"

   ---------- Footnotes ----------

   (1) The Forth standard has words with undefined interpretation
semantics (e.g., 'r@') and words without defined execution semantics
(e.g., 's"') and words with neither (e.g., 'if'), but in cases where
both interpretation and execution semantics are defined, they are the
same; so we treat them as being the same.

6.12.2 Name token
-----------------

Gforth represents named words by the "name token", (nt).  The name token
is a cell-sized abstract data type that occurs as argument or result of
the words below.

   Since Gforth 1.0, for most words the concrete implementation of their
nt is the same address as its xt (this is the primary nt for the xt).
However, synonyms, aliases, and words defined with 'interpret/compile:'
get their xt from another word, but still have an nt of their own (that
is different from the xt).  Therefore, you cannot use xts and nts
interchangeably, even if you are prepared to write code specific to
Gforth 1.0.  You do not get these alternate nts for the xt with '>name'.

   You get the nt of a word x with '``x' (since Gforth 1.0) or with

'find-name' ( c-addr u -- nt | 0  ) gforth-0.2 "find-name"
   Find the name c-addr u in the current search order.  Return its nt,
if found, otherwise 0.

'find-name-in' ( c-addr u wid -- nt | 0  ) gforth-1.0 "find-name-in"
   search the word list identified by wid for the definition named by
the string at c-addr u.  Return its nt, if found, otherwise 0.

'latest' ( -- nt  ) gforth-0.6 "latest"
   NT is the name token of the last word defined; it is 0 if the last
word has no name.

'latestnt' ( -- nt  ) gforth-1.0 "latestnt"
   nt is the name token of the last word defined.

'>name' ( xt -- nt|0  ) gforth-0.2 "to-name"
   The primary name token nt of the word represented by xt.  Returns 0
if xt is not an xt (using a heuristic check that has a small chance of
misidentifying a non-xt as xt), or if the primary nt is of an unnamed
word.  As of Gforth 1.0, every xt has a primary nt, but other named
words may have the same interpretation sematics xt.

'xt>name' ( xt -- nt  ) gforth-1.0 "xt-to-name"
   Produces the primary nt for an xt.  If xt is not an xt, nt is not
guaranteed to be an nt.

   You can get all the nts in a wordlist with

'traverse-wordlist' ( ... xt wid -- ...  ) tools-ext "traverse-wordlist"
   perform xt ( ...  nt -- f ...  )  once for every word nt in the
wordlist wid, until f is false or the wordlist is exhausted.  xt is free
to use the stack underneath.

   You can use the nt to access the interpretation and compilation
semantics of a word, its name, and the next word in the wordlist:

'name>interpret' ( nt -- xt  ) tools-ext "name-to-interpret"
   xt represents the interpretation semantics of the word nt.

'name>compile' ( nt -- w xt  ) tools-ext "name-to-compile"
   w xt is the compilation token for the word nt.

'name>string' ( nt -- addr u  ) tools-ext "name-to-string"
   addr count is the name of the word represented by nt.

'id.' ( nt --  ) gforth-0.6 "i-d-dot"
   Print the name of the word represented by NT.

'.id' ( nt --  ) gforth-0.6 "dot-i-d"
   F83 name for 'id.'.

'name>link' ( nt1 -- nt2 / 0  ) gforth-1.0 "name-to-link"
   For a word nt1, returns the previous word nt2 in the same wordlist,
or 0 if there is no previous word.

   A nameless word usually has no interpretation nor compilation
semantics, no name, and it's not in a wordlist.  But in Gforth (since
1.0) all words are equal, so even nameless words have an nt (but they
are in no wordlist).  You can get that nt with 'latestnt', and the words
above that consume nts do something reasonable for these nts.

   As a usage example, the following code lists all the words in
'forth-wordlist' with non-default compilation semantics:

     : ndcs-words ( wid -- )
       [: dup name>compile ['] compile, <> if over id. then 2drop true ;]
       swap traverse-wordlist ;

     forth-wordlist ndcs-words

   This code assumes that a word has default compilation semantics if
the xt part of its compilation token is the xt of 'compile,'.

   The closest thing to the nt in older Forth systems is the name field
address (NFA), but there are significant differences: in older Forth
systems each word had a unique NFA, LFA, CFA and PFA (in this order, or
LFA, NFA, CFA, PFA) and there were words for getting from one to the
next.  In contrast, in Gforth several nts can get the same xt from
'name>interpret' xt; there is a link field in the structure identified
by the name token, but searching usually uses a hash table external to
these structures; the name in Gforth has a cell-wide count-and-flags
field, and the nt is not implemented as the address of that count field.

6.12.3 Compilation token
------------------------

The compilation semantics of a named word is represented by a
"compilation token" consisting of two cells: w xt.  The top cell xt is
an execution token.  The compilation semantics represented by the
compilation token can be performed with 'execute', which consumes the
whole compilation token, with an additional stack effect determined by
the represented compilation semantics.

   At present, the w part of a compilation token is an execution token,
and the xt part represents either 'execute' or 'compile,'(1).  However,
don't rely on that knowledge, unless necessary; future versions of
Gforth may introduce unusual compilation tokens (e.g., a compilation
token that represents the compilation semantics of a literal).

   You get the compilation token of, e.g., 'if' in a standard way with
'name>compile', e.g., '`if name>compile', but there are also parsing
words to get the compilation token of a word:

'[COMP']' ( compilation "name" -- ; run-time -- w xt  ) gforth-0.2 "bracket-comp-tick"
   Compilation token w xt represents name's compilation semantics.

'COMP'' ( "name" -- w xt  ) gforth-0.2 "comp-tick"
   Compilation token w xt represents name's compilation semantics.

   You can perform the compilation semantics represented by the
compilation token with 'execute'.  You can compile the compilation
semantics with 'postpone,'.  I.e., '``x name>compile postpone,' is
equivalent to 'postpone x'.

'postpone,' ( w xt --  ) gforth-0.2 "postpone-comma"
   Compile the compilation semantics represented by the compilation
token w xt.

   ---------- Footnotes ----------

   (1) Depending upon the compilation semantics of the word.  If the
word has default compilation semantics, the xt will represent
'compile,'.  Otherwise (e.g., for immediate words), the xt will
represent 'execute'.

6.13 Compiling words
====================

In contrast to most other languages, Forth has no strict boundary
between compilation and run-time.  E.g., you can run arbitrary code
between defining words (or for computing data used by defining words
like 'constant').  Moreover, 'Immediate' (*note Interpretation and
Compilation Semantics:: and '['...']'  (see below) allow running
arbitrary code while compiling a colon definition (exception: you must
not allot dictionary space).

6.13.1 Literals
---------------

The simplest and most frequent example is to compute a literal during
compilation.  E.g., the following definition prints an array of strings,
one string per line:

     : .strings ( addr u -- ) \ gforth
         2* cells bounds U+DO
     	cr i 2@ type
         2 cells +LOOP ;

   With a simple-minded compiler like Gforth's, this computes '2 cells'
on every loop iteration.  You can compute this value once and for all at
compile time and compile it into the definition like this:

     : .strings ( addr u -- ) \ gforth
         2* cells bounds U+DO
     	cr i 2@ type
         [ 2 cells ] literal +LOOP ;

   '[' switches the text interpreter to interpret state (you will get an
'ok' prompt if you type this example interactively and insert a newline
between '[' and ']'), so it performs the interpretation semantics of '2
cells'; this computes a number.  ']'  switches the text interpreter back
into compile state.  It then performs 'Literal''s compilation semantics,
which are to compile this number into the current word.  You can
decompile the word with 'see .strings' to see the effect on the compiled
code.

   You can also optimize the '2* cells' into '[ 2 cells ] literal *' in
this way.

'[' ( --  ) core "left-bracket"
   Enter interpretation state.  Immediate word.

']' ( --  ) core "right-bracket"
   Enter compilation state.

'Literal' ( compilation n -- ; run-time -- n  ) core "Literal"
   Compilation semantics: compile the run-time semantics.
Run-time Semantics: push n.
Interpretation semantics: undefined.

'ALiteral' ( compilation addr -- ; run-time -- addr  ) gforth-0.2 "ALiteral"
   Works like 'literal', but (when used in cross-compiled code) tells
the cross-compiler that the literal is an address.

']L' ( compilation: n -- ; run-time: -- n  ) gforth-0.5 "]L"
   equivalent to '] literal'

   There are also words for compiling other data types than single cells
as literals:

'2Literal' ( compilation w1 w2 -- ; run-time  -- w1 w2  ) double "two-literal"
   Compile appropriate code such that, at run-time, w1 w2 are placed on
the stack.  Interpretation semantics are undefined.

'FLiteral' ( compilation r -- ; run-time -- r  ) floating "f-literal"
   Compile appropriate code such that, at run-time, r is placed on the
(floating-point) stack.  Interpretation semantics are undefined.

'SLiteral' ( Compilation c-addr1 u ; run-time -- c-addr2 u  ) string "SLiteral"
   Compilation: compile the string specified by c-addr1, u into the
current definition.  Run-time: return c-addr2 u describing the address
and length of the string.

   You might be tempted to pass data from outside a colon definition to
the inside on the data stack.  This does not work, because ':' puhes a
colon-sys, making stuff below unaccessible.  E.g., this does not work:

     5 : foo literal ; \ error: "unstructured"

   Instead, you have to pass the value in some other way, e.g., through
a variable:

     variable temp
     5 temp !
     : foo [ temp @ ] literal ;

6.13.2 Macros
-------------

'Literal' and friends compile data values into the current definition.
You can also write words that compile other words into the current
definition.  E.g.,

     : compile-+ ( -- ) \ compiled code: ( n1 n2 -- n )
       POSTPONE + ;

     : foo ( n1 n2 -- n )
       [ compile-+ ] ;
     1 2 foo .

   This is equivalent to ': foo + ;' ('see foo' to check this).  What
happens in this example?  'Postpone' compiles the compilation semantics
of '+' into 'compile-+'; later the text interpreter executes 'compile-+'
and thus the compilation semantics of +, which compile (the execution
semantics of) '+' into 'foo'.(1)

'postpone' ( "name" --  ) core "postpone"
   Compiles the compilation semantics of name.

   Compiling words like 'compile-+' are usually immediate (or similar)
so you do not have to switch to interpret state to execute them;
modifying the last example accordingly produces:

     : [compile-+] ( compilation: --; interpretation: -- )
       \ compiled code: ( n1 n2 -- n )
       POSTPONE + ; immediate

     : foo ( n1 n2 -- n )
       [compile-+] ;
     1 2 foo .

   You will occassionally find the need to POSTPONE several words;
putting POSTPONE before each such word is cumbersome, so Gforth provides
a more convenient syntax: ']] ... [['.  This allows us to write
'[compile-+]' as:

     : [compile-+] ( compilation: --; interpretation: -- )
       ]] + [[ ; immediate

']]' ( --  ) gforth-0.6 "right-bracket-bracket"
   Switch into postpone state: All words and recognizers are processed
as if they were preceded by 'postpone'.  Postpone state ends when '[['
is recognized.

   The unusual direction of the brackets indicates their function: ']]'
switches from compilation to postponing (i.e., compilation of
compilation), just like ']' switches from immediate execution
(interpretation) to compilation.  Conversely, '[[' switches from
postponing to compilation, ananlogous to '[' which switches from
compilation to immediate execution.

   The real advantage of ']] '...' [[' becomes apparent when there are
many words to POSTPONE. E.g., the word 'compile-map-array' (*note
Advanced macros Tutorial::) can be written much shorter as follows:

     : compile-map-array ( compilation: xt -- ; run-time: ... addr u -- ... )
     \ at run-time, execute xt ( ... x -- ... ) for each element of the
     \ array beginning at addr and containing u elements
       {: xt: xt :}
       ]] cells over + swap ?do
         i @ xt 1 cells +loop [[ ;

     : sum-array ( addr u -- n )
       0 [ ' + compile-map-array ] ;

   If you then say 'see sum-array', it shows the following code:

     : sum-array
       #0 over + swap ?do
         i  + #8 +LOOP
     ;

   In addition to ']]'...'[[', this example shows off some other
features:

   * It uses a defer-flavoured (defined with 'xt:' local 'xt';
     mentioning the local inside ']]'...'[[' results in 'compile,'ing
     the xt in the local.

   * It uses the literal '1' inside ']]'...'[['.  This results in
     'postpone'ing the '1', i.e.  compiling it when 'compile-map-array'
     is run.

   * When 'compile-map-array' is run, '1 cells' is compiled and
     optimized into '#8' by Gforth's constant folding.

   Note that parsing words such as 's\"' don't parse at postpone time
and therefore not inside ']]'...'[['.  Instead of 's\" mystring\n"' you
can use the string recognizer and write '"mystring\n"', which works
inside ']]'...'[['.  Likewise for the parsing word '[']' and the
recognizer notation starting with '`'.

   But if you prefer to use 's\"' (or have a parsing word that has no
recognizer replacement), you can do it by switching back to compilation:

     ]] ... [[ s\" mystring\n" ]] 2literal ... [[

   Definitions of ']]' and friends in Standard Forth are provided in
'compat/macros.fs'.

   Immediate compiling words are similar to macros in other languages
(in particular, Lisp).  The important differences to macros in, e.g., C
are:

   * You use the same language for defining and processing macros, not a
     separate preprocessing language and processor.

   * Consequently, the full power of Forth is available in macro
     definitions.  E.g., you can perform arbitrarily complex
     computations, or generate different code conditionally or in a loop
     (e.g., *note Advanced macros Tutorial::).  This power is very
     useful when writing a parser generators or other code-generating
     software.

   * Macros defined using 'postpone' etc.  deal with the language at a
     higher level than strings; name binding happens at macro definition
     time, so you can avoid the pitfalls of name collisions that can
     happen in C macros.  Of course, Forth is a liberal language and
     also allows to shoot yourself in the foot with text-interpreted
     macros like

          : [compile-+] s" +" evaluate ; immediate

     Apart from binding the name at macro use time, using 'evaluate'
     also makes your definition 'state'-smart (*note state-smartness::).

   You may want the macro to compile a number into a word.  The word to
do it is 'literal', but you have to 'postpone' it, so its compilation
semantics take effect when the macro is executed, not when it is
compiled:

     : [compile-5] ( -- ) \ compiled code: ( -- n )
       5 POSTPONE literal ; immediate

     : foo [compile-5] ;
     foo .

   You may want to pass parameters to a macro, that the macro should
compile into the current definition.  If the parameter is a number, then
you can use 'postpone literal' (similar for other values).

   If you want to pass a word that is to be compiled, the usual way is
to pass an execution token and 'compile,' it:

     : twice1 ( xt -- ) \ compiled code: ... -- ...
       dup compile, compile, ;

     : 2+ ( n1 -- n2 )
       [ ' 1+ twice1 ] ;

'compile,' ( xt --  ) core-ext "compile-comma"
   Append the semantics represented by xt to the current definition.
When the resulting code fragment is run, it behaves the same as if xt is
'execute'd.

   An alternative available in Gforth, that allows you to pass the
compilation semantics as parameters is to use the compilation token
(*note Compilation token::).  The same example in this technique:

     : twice ( ... ct -- ... ) \ compiled code: ... -- ...
       2dup 2>r execute 2r> execute ;

     : 2+ ( n1 -- n2 )
       [ comp' 1+ twice ] ;

   In the example above '2>r' and '2r>' ensure that 'twice' works even
if the executed compilation semantics has an effect on the data stack.

   You can also define complete definitions with these words; this
provides an alternative to using 'does>' (*note User-defined Defining
Words::).  E.g., instead of

     : curry+ ( n1 "name" -- )
         CREATE ,
     DOES> ( n2 -- n1+n2 )
         @ + ;

   you could define

     : curry+ ( n1 "name" -- )
       \ name execution: ( n2 -- n1+n2 )
       >r : r> POSTPONE literal POSTPONE + POSTPONE ; ;

     -3 curry+ 3-
     see 3-

   The sequence '>r : r>' is necessary, because ':' puts a colon-sys on
the data stack that makes everything below it unaccessible.

   This way of writing defining words is sometimes more, sometimes less
convenient than using 'does>' (*note Advanced does> usage example::).
One advantage of this method is that it can be optimized better, because
the compiler knows that the value compiled with 'literal' is fixed,
whereas the data associated with a 'create'd word can be changed.

'[compile]' ( compilation "name" -- ; run-time ? -- ?  ) core-ext "bracket-compile"
   Legacy word.  Use 'postpone' instead.  Works like 'postpone' if name
has non-default compilation semantics.  If name has default compilation
semantics (i.e., is a normal word), compiling '[compile] name' is
equivalent to compiling name (i.e.  '[compile]' is redundant in this
case.

   ---------- Footnotes ----------

   (1) A recent RFI answer requires that compiling words should only be
executed in compile state, so this example is not guaranteed to work on
all standard systems, but on any decent system it will work.

6.14 The Text Interpreter
=========================

The text interpreter(1) is an endless loop that processes input from the
current input device.  It is also called the outer interpreter, in
contrast to the inner interpreter (*note Engine::) which executes the
compiled Forth code on interpretive implementations.

   The text interpreter operates in one of two states: "interpret state"
and "compile state".  The current state is defined by the aptly-named
variable 'state'.

   This section starts by describing how the text interpreter behaves
when it is in interpret state, processing input from the user input
device -- the keyboard.  This is the mode that a Forth system is in after
it starts up.

   The text interpreter works from an area of memory called the "input
buffer"(2), which stores your keyboard input when you press the <RET>
key.  Starting at the beginning of the input buffer, it skips leading
spaces (called "delimiters") then parses a string (a sequence of
non-space characters) until it reaches either a space character or the
end of the buffer.  Having parsed a string, it makes two attempts to
process it:

   * It looks for the string in a "dictionary" of definitions.  If the
     string is found, the string names a "definition" (also known as a
     "word") and the dictionary search returns information that allows
     the text interpreter to perform the word's "interpretation
     semantics".  In most cases, this simply means that the word will be
     executed.
   * If the string is not found in the dictionary, the text interpreter
     attempts to treat it as a number, using the rules described in
     *note Number Conversion::.  If the string represents a legal number
     in the current radix, the number is pushed onto a parameter stack
     (the data stack for integers, the floating-point stack for
     floating-point numbers).

   If both attempts fail, the text interpreter discards the remainder of
the input buffer, issues an error message and waits for more input.  If
one of the attempts succeeds, the text interpreter repeats the parsing
process until the whole of the input buffer has been processed, at which
point it prints the status message "' ok'" and waits for more input.

   The text interpreter keeps track of its position in the input buffer
by updating a variable called '>IN' (pronounced "to-in").  The value of
'>IN' starts out as 0, indicating an offset of 0 from the start of the
input buffer.  The region from offset '>IN @' to the end of the input
buffer is called the "parse area"(3).  This example shows how '>IN'
changes as the text interpreter parses the input buffer:

     : remaining source >in @ /string
       cr ." ->" type ." <-" ; immediate

     1 2 3 remaining + remaining .

     : foo 1 2 3 remaining swap remaining ;

The result is:

     ->+ remaining .<-
     ->.<-5  ok

     ->SWAP remaining ;-<
     ->;<-  ok

   The value of '>IN' can also be modified by a word in the input buffer
that is executed by the text interpreter.  This means that a word can
"trick" the text interpreter into either skipping a section of the input
buffer(4) or into parsing a section twice.  For example:

     : lat ." <<foo>>" ;
     : flat ." <<bar>>" >IN DUP @ 3 - SWAP ! ;

When 'flat' is executed, this output is produced(5):

     <<bar>><<foo>>

   This technique can be used to work around some of the
interoperability problems of parsing words.  Of course, it's better to
avoid parsing words where possible.

Two important notes about the behaviour of the text interpreter:

   * It processes each input string to completion before parsing
     additional characters from the input buffer.
   * It treats the input buffer as a read-only region (and so must your
     code).

When the text interpreter is in compile state, its behaviour changes in
these ways:

   * If a parsed string is found in the dictionary, the text interpreter
     will perform the word's "compilation semantics".  In most cases,
     this simply means that the execution semantics of the word will be
     appended to the current definition.
   * When a number is encountered, it is compiled into the current
     definition (as a literal) rather than being pushed onto a parameter
     stack.
   * If an error occurs, 'state' is modified to put the text interpreter
     back into interpret state.
   * Each time a line is entered from the keyboard, Gforth prints "'
     compiled'" rather than " 'ok'".

   When the text interpreter is using an input device other than the
keyboard, its behaviour changes in these ways:

   * When the parse area is empty, the text interpreter attempts to
     refill the input buffer from the input source.  When the input
     source is exhausted, the input source is set back to the previous
     input source.
   * It doesn't print out "' ok'" or "' compiled'" messages each time
     the parse area is emptied.
   * If an error occurs, the input source is set back to the user input
     device.

   You can read about this in more detail in *note Input Sources::.

'>in' ( -- addr  ) core "to-in"
   'uvar' variable -- a-addr is the address of a cell containing the char
offset from the start of the input buffer to the start of the parse
area.

'source' ( -- addr u  ) core "source"
   Return address addr and length u of the current input buffer

'tib' ( -- addr  ) core-ext-obsolescent "t-i-b"

'#tib' ( -- addr  ) core-ext-obsolescent "number-t-i-b"
   'uvar' variable -- a-addr is the address of a cell containing the
number of characters in the terminal input buffer.  OBSOLESCENT:
'source' superceeds the function of this word.

'interpret' ( ... -- ...  ) gforth-0.2 "interpret"

   ---------- Footnotes ----------

   (1) This is an expanded version of the material in *note Introducing
the Text Interpreter::.

   (2) When the text interpreter is processing input from the keyboard,
this area of memory is called the "terminal input buffer" (TIB) and is
addressed by the (obsolescent) words 'TIB' and '#TIB'.

   (3) In other words, the text interpreter processes the contents of
the input buffer by parsing strings from the parse area until the parse
area is empty.

   (4) This is how parsing words work.

   (5) Exercise for the reader: what would happen if the '3' were
replaced with '4'?

6.14.1 Input Sources
--------------------

By default, the text interpreter processes input from the user input
device (the keyboard) when Forth starts up.  The text interpreter can
process input from any of these sources:

   * The user input device -- the keyboard.
   * A file, using the words described in *note Forth source files::.
   * A block, using the words described in *note Blocks::.
   * A text string, using 'evaluate'.

   A program can identify the current input device from the values of
'source-id' and 'blk'.

'source-id' ( -- 0 | -1 | fileid  ) core-ext,file "source-i-d"
   Return 0 (the input source is the user input device), -1 (the input
source is a string being processed by 'evaluate') or a fileid (the input
source is the file specified by fileid).

'blk' ( -- addr  ) block "b-l-k"
   'uvar' variable -- This cell contains the current block number (or 0
if the current input source is not a block).

'save-input' ( -- x1 .. xn n  ) core-ext "save-input"
   The n entries xn - x1 describe the current state of the input source
specification, in some platform-dependent way that can be used by
'restore-input'.

'restore-input' ( x1 .. xn n -- flag  ) core-ext "restore-input"
   Attempt to restore the input source specification to the state
described by the n entries xn - x1.  flag is true if the restore fails.
In Gforth with the new input code, it fails only with a flag that can be
used to throw again; it is also possible to save and restore between
different active input streams.  Note that closing the input streams
must happen in the reverse order as they have been opened, but in
between everything is allowed.

'evaluate' ( ... addr u -- ...  ) core,block "evaluate"
   Save the current input source specification.  Store '-1' in
'source-id' and '0' in 'blk'.  Set '>IN' to '0' and make the string
c-addr u the input source and input buffer.  Interpret.  When the parse
area is empty, restore the input source specification.

'query' ( --  ) core-ext-obsolescent "query"
   Make the user input device the input source.  Receive input into the
Terminal Input Buffer.  Set '>IN' to zero.  OBSOLESCENT: superceeded by
'accept'.

6.14.2 Number Conversion
------------------------

You get an overview of how the text interpreter converts its numeric
input in *note Literals in source code::.  This section describes some
related words.

   By default, the number base used for integer number conversion is
given by the contents of the variable 'base'.  Note that a lot of
confusion can result from unexpected values of 'base'.  If you change
'base' anywhere, make sure to save the old value and restore it
afterwards; better yet, use 'base-execute', which does this for you.  In
general I recommend keeping 'base' decimal, and using the prefixes
described in *note Literals in source code:: for the popular non-decimal
bases.

'base-execute' ( i*x xt u -- j*x  ) gforth-0.7 "base-execute"
   execute xt with the content of 'BASE' being u, and restoring the
original 'BASE' afterwards.

'base' ( -- a-addr  ) core "base"
   'User' variable -- a-addr is the address of a cell that stores the
number base used by default for number conversion during input and
output.  Don't store to 'base', use 'base-execute' instead.

'hex' ( --  ) core-ext "hex"
   Set 'base' to &16 (hexadecimal).  Don't use 'hex', use 'base-execute'
instead.

'decimal' ( --  ) core "decimal"
   Set 'base' to &10 (decimal).  Don't use 'decimal', use 'base-execute'
instead.

'dpl' ( -- a-addr  ) gforth-0.2 "Decimal-PLace"
   'User' variable -- a-addr is the address of a cell that stores the
position of the decimal point in the most recent numeric conversion.
Initialised to -1.  After the conversion of a number containing no
decimal point, 'dpl' is -1.  After the conversion of '2.' it holds 0.
After the conversion of 234123.9 it contains 1, and so forth.

Number conversion has a number of traps for the unwary:

   * You cannot determine the current number base using the code
     sequence 'base @ .' -- the number base is always 10 in the current
     number base.  Instead, use something like 'base @ dec.'
   * There is a word 'bin' but it does not set the number base!  (*note
     General files::).
   * Standard Forth requires the '.' of a double-precision number to be
     the final character in the string.  Gforth allows the '.' to be
     anywhere.
   * The number conversion process does not check for overflow.

   You can read numbers into your programs with the words described in
*note Line input and conversion::.

6.14.3 Interpret/Compile states
-------------------------------

A standard program is not permitted to change 'state' explicitly.
However, it can change 'state' implicitly, using the words '[' and ']'.
When '[' is executed it switches 'state' to interpret state, and
therefore the text interpreter starts interpreting.  When ']' is
executed it switches 'state' to compile state and therefore the text
interpreter starts compiling.  The most common usage for these words is
for switching into interpret state and back from within a colon
definition; this technique can be used to compile a literal (for an
example, *note Literals::) or for conditional compilation (for an
example, *note Interpreter Directives::).

6.14.4 Interpreter Directives
-----------------------------

These words are usually used in interpret state; typically to control
which parts of a source file are processed by the text interpreter.
There are only a few Standard Forth Standard words, but Gforth
supplements these with a rich set of immediate control structure words
to compensate for the fact that the non-immediate versions can only be
used in compile state (*note Control Structures::).  Typical usage:

     [undefined] \G [if]
       : \G ... ; immediate
     [endif]

   So if the system does not define '\G', compile some replacement code
(with possibly reduced functionality).

'[IF]' ( flag --  ) tools-ext "bracket-if"
   If flag is 'TRUE' do nothing (and therefore execute subsequent words
as normal).  If flag is 'FALSE', parse and discard words from the parse
area (refilling it if necessary using 'REFILL') including nested
instances of '[IF]'..  '[ELSE]'..  '[THEN]' and '[IF]'..  '[THEN]' until
the balancing '[ELSE]' or '[THEN]' has been parsed and discarded.
Immediate word.

'[ELSE]' ( --  ) tools-ext "bracket-else"
   Parse and discard words from the parse area (refilling it if
necessary using 'REFILL') including nested instances of '[IF]'..
'[ELSE]'..  '[THEN]' and '[IF]'..  '[THEN]' until the balancing '[THEN]'
has been parsed and discarded.  '[ELSE]' only gets executed if the
balancing '[IF]' was 'TRUE'; if it was 'FALSE', '[IF]' would have parsed
and discarded the '[ELSE]', leaving the subsequent words to be executed
as normal.  Immediate word.

'[THEN]' ( --  ) tools-ext "bracket-then"
   Do nothing; used as a marker for other words to parse and discard up
to.  Immediate word.

'[ENDIF]' ( --  ) gforth-0.2 "bracket-end-if"
   Do nothing; synonym for '[THEN]'

'[defined]' ( "<spaces>name" -- flag  ) tools-ext "bracket-defined"
   returns true if name is found in current search order

'[undefined]' ( "<spaces>name" -- flag  ) tools-ext "bracket-undefined"
   returns false if name is found in current search order

'[IFDEF]' ( "<spaces>name" --  ) gforth-0.2 "bracket-if-def"
   If name is found in the current search-order, behave like '[IF]' with
a 'TRUE' flag, otherwise behave like '[IF]' with a 'FALSE' flag.
Immediate word.

'[IFUNDEF]' ( "<spaces>name" --  ) gforth-0.2 "bracket-if-un-def"
   If name is not found in the current search-order, behave like '[IF]'
with a 'TRUE' flag, otherwise behave like '[IF]' with a 'FALSE' flag.
Immediate word.

'[?DO]' ( n-limit n-index --  ) gforth-0.2 "bracket-question-do"

'[DO]' ( n-limit n-index --  ) gforth-0.2 "bracket-do"

'[LOOP]' ( --  ) gforth-0.2 "bracket-loop"

'[+LOOP]' ( n --  ) gforth-0.2 "bracket-question-plus-loop"

'[FOR]' ( n --  ) gforth-0.2 "bracket-for"

'[NEXT]' ( n --  ) gforth-0.2 "bracket-next"

'[I]' ( run-time -- n  ) gforth-0.2 "bracket-i"
   At run-time, '[I]' pushes the loop index of the
text-interpretation-time '[do]' iteration.  If you want to process the
index at interpretation time, interpret '[I]' interpretevely, or use
'INT-[I]'.

'INT-[I]' ( -- n  ) gforth-1.0 "int-bracket-i"
   Push the loop index of the '[do]' iteration at text interpretation
time.

'[BEGIN]' ( --  ) gforth-0.2 "bracket-begin"

'[UNTIL]' ( flag --  ) gforth-0.2 "bracket-until"

'[AGAIN]' ( --  ) gforth-0.2 "bracket-again"

'[WHILE]' ( flag --  ) gforth-0.2 "bracket-while"

'[REPEAT]' ( --  ) gforth-0.2 "bracket-repeat"

   You can use '#line' to change Gforth's idea about the current source
line number and source file.  This is useful in cases where the Forth
file is generated from some other source code file, and you want to get,
e.g.  error messages etc.  that refer to the original source code; then
the Forth-code generator needs to insert '#line' lines in the Forth code
wherever appropriate.

'#line' ( "u" "["file"]" --  ) gforth-1.0 "#line"
   Set the line number to u and (if present) the file name to file.
Consumes the rest of the line.

6.14.5 Recognizers
------------------

When the text interpreter processes source code, it divides the code
into blank-delimited strings, and then calls recognizers to identify
them as words, numbers, etc., until one recognizer identifies
(recognizes) the string; if the string is not recognized, the text
interpreter reports an error ('undefined word').

   The usual way to deal with recognizers is to just write code that one
of them identifies (*note Default Recognizers::); however, you can also
manipulate them (*note Dealing with existing Recognizers::) or even
define new ones (*note Defining Recognizers::).

6.14.5.1 Default Recognizers
............................

The standard Forth text interpreter recognizes words in the search order
('rec-nt'), integer numbers ('rec-num'), and floating point numbers
('rec-float').  By default Gforth also recognizes syntaxes for

   * strings, e.g., '"mystring"', with 'rec-string'

   * complex numbers, e.g., '0e+1ei', with 'rec-complex'

   * storing a value or changing a defered word, e.g., '->myvalue', with
     'rec-to'

   * the xt representing the interpretation semantics of a word, e.g.,
     '`dup', with 'rec-tick'

   * the nt of a word, e.g., '``mysynonym', with 'rec-dtick'

   * an address in the body of a word, e.g., '<myarray+8>', with
     'rec-body'

   * an access to an environment variable of the operating system, e.g.,
     '${HOME}', with 'rec-env'

   * a word in a vocabulary, e.g., 'myvoc1:myvoc2:myword', with
     'rec-scope'

   * using a specific recognizer to recognize something, e.g.,
     'float?1.', , with 'rec-meta'

   You can use 'locate' (*note Locating source code definitions::) to
determine which recognizer recognizes a piece of source code.  E.g.:

     defer mydefer
     locate ->mydefer

   will show that 'rec-to' recognizes '->mydefer'.  However, if the
recognizer recognizes a dictionary word (e.g., the scope recognizer),
locate will show that word.

   You can see which recognizers are used and the order of recognizers
with

'.recognizers' ( --  ) gforth-experimental "dot-recognizers"
   Print the current recognizer order, with the first-searched
recognizer leftmost (unlike .order).  The inverted '~' is displayed
instead of 'rec-', which is the common prefix of all recognizers.

   Recognizers are typically designed to avoid matching the same strings
as other recognizers.  E.g., 'rec-env' (the environment variable
recognizer) requires braces to avoid a conflict with the number
recognizer for input strings like '$ADD'.  There are a few exceptions to
this policy, however:

   * Word names can be anything, so they can conflict with any other
     recognizer (and the search order is searched before other
     recognizers).

     However, they tend not to start with '0' (and if they do, they
     contain special characters), so if your base is 'hex', it is a good
     practice to let your numbers start with '0'.

     In the code bases we have looked at, starting words with ''' (quote
     aka tick) is much more common than starting them with '`'
     (backquote aka backtick), so the recognizers for the xt and the nt
     use '`' to reduce the number of conflicts.

   * Both the integer recognizer 'rec-num' and the floating-point
     recognizer 'rec-float' recognize, e.g., '1.'.  Because 'rec-num' is
     (by default) first, '1.' is recognized as a double-cell integer.
     If you change the recognizer order to use 'rec-float' first, '1.'
     is recognized as a floating-point number, but loading code written
     in standard Forth may behave in a non-standard way.

     In any case, it's a good practice to avoid that conflict in your
     own code as follows: Always write double-cell integers with a
     number prefix, e.g., '#1.'; and always write floating-point numbers
     with an 'e', e.g., '1e'.

   * We have seen a few word names that start with '->'.  You can avoid
     a conflict by using 'to myvalue' or 'to?->myvalue' (the latter
     works with 'postpone').

6.14.5.2 Dealing with existing Recognizers
..........................................

A recognizer is a word to which you pass a string.  If the recognizer
recognizes the string, it typically returns some data and the xt of a
word for processing the data; this word is called the translator.  If
the recognizer does not recognize the string, it returns the xt of
'notfound'.

   All recognizers have the stack effect ( c-addr u -- ...  xt ).

   Recognizers take a string and return some data and a translator for
interpreting that data.  Gforth implements that translator as xt
(executing it will perform the appropriate action to handle the token in
the current state), but other Forth systems may implement it as actual
table, with three xts inside.  The first xt is the
interpretation/run-time xt, it performs the interpretation semantics on
the data (usually, this means it just leaves the data on the stack).
The second xt performs the compilation semantics, it gets the data and
the run-time semantics xt.  The third xt perfoms the postpone semantics,
it also gets the data and the run-time semantics xt.  You can use
'>postpone' to postpone the run-time xt.

   Recognizers are organized as stack, so you can arrange the sequence
of recognizers in the same way as the vocabulary stack.  Recognizer
stacks are themselves recognizers, i.e.  they are executable, take a
string and return a translator.

'notfound' ( state --  ) gforth-experimental "notfound"
   If a recognizer fails, it returns 'notfound'

'rec-nt' ( addr u -- nt translate-nt | notfound  ) gforth-experimental "rec-nt"
   recognize a name token

'rec-num' ( addr u -- n/d table | notfound  ) gforth-experimental "rec-num"
   converts a number to a single/double integer

'rec-float' ( addr u -- r translate-float | notfound  ) gforth-experimental "rec-float"
   recognize floating point numbers

'rec-string' ( addr u -- addr u' r:string | rectype-null  ) gforth-experimental "rec-string"
   Convert strings enclosed in double quotes into string literals,
escapes are treated as in 'S\"'.

'rec-to' ( addr u -- xt n r:to | rectype-null  ) gforth-experimental "rec-to"
   words prefixed with '->' are treated as if preceeded by 'TO', with
'+>' as '+TO', with ''>' as 'ADDR', with '@>' as 'ACTION-OF', and with
'=>' as 'IS'.

'rec-tick' ( addr u -- xt rectype-num | rectype-null  ) gforth-experimental "rec-tick"
   words prefixed with '`' return their xt.  Example: '`dup' gives the
xt of dup

'rec-dtick' ( addr u -- nt rectype-num | rectype-null  ) gforth-experimental "rec-dtick"
   words prefixed with '``' return their nt.  Example: '``S"' gives the
nt of 'S"'

'rec-body' ( addr u -- xt translate-tick | translate-null  ) gforth-experimental "rec-body"
   words bracketed with ''<'' ''>'' return their body.  Example: '<dup>'
gives the body of dup

'get-recognizers' ( -- xt1 .. xtn n  ) gforth-experimental "get-recognizers"
   push the content on the recognizer stack

'set-recognizers' ( xt1 .. xtn n --  ) gforth-experimental "set-recognizers"
   set the recognizer stack from content on the stack

'recognize' ( addr u rec-addr -- ... rectype  ) gforth-experimental "recognize"
   apply a recognizer stack to a string, delivering a token

'recognizer-sequence:' ( xt1 .. xtn n "name" --  ) gforth-experimental "recognizer-sequence:"
   concatenate a stack of recognizers to one recognizer with the name
"name".  xtn is tried first, xt1 last, just like on the recognizer stack

'forth-recognize' ( c-addr u -- ... translate-xt  ) recognizer "forth-recognize"
   The system recognizer

'forth-recognizer' ( -- xt  ) gforth-experimental "forth-recognizer"
   backward compatible to Matthias Trute recognizer API. This construct
turns a deferred word into a value-like word.

'set-forth-recognize' ( xt --  ) recognizer "set-forth-recognize"
   Change the system recognizer

'translate:' ( int-xt comp-xt post-xt "name" --  ) gforth-experimental "translate:"
   create a new recognizer table.  Items are in order of STATE value,
which are 0 or negative.  Up to 7 slots are available for extensions.

'translate-nt' ( i*x nt -- j*x  ) gforth-experimental "translate-nt"
   translate a name token

'translate-num' ( x -- | x  ) gforth-experimental "translate-num"
   translate a number

'translate-dnum' ( dx -- | dx  ) gforth-experimental "translate-dnum"
   translate a double number

   doc-translate-float
'try-recognize' ( addr u xt -- results | false  ) gforth-experimental "try-recognize"
   For nested recognizers: try to recognize ADDR U, and execute XT to
check if the result is desired.  If XT returns false, clean up all side
effects of the recognizer, and return false.  Otherwise return the
results of the call to XT, of which the topmost is non-zero.

'>interpret' ( translator --  ) gforth-experimental ">interpret"
   perform interpreter action of translator

'>compile' ( translator --  ) gforth-experimental ">compile"
   perform compile action of translator

'>postpone' ( translator --  ) gforth-experimental ">postpone"
   perform postpone action of translator

'translate-method:' ( "name" --  ) gforth-experimental "translate-method:"
   create a new translate method, extending the translator table.  You
can assign an xt to an existing rectype by using XT RECTYPE 'to'
TRANSLATOR.

'translate-state' ( xt --  ) gforth-experimental "translate-state"
   change the current state of the system so that executing a translator
matches the translate-method passsed as XT

6.14.5.3 Defining Recognizers
.............................

6.14.6 Text Interpreter Hooks
-----------------------------

'before-line' ( --  ) gforth-1.0 "before-line"
   Deferred word called before the text interpreter parses the next line

'before-word' ( --  ) gforth-0.7 "before-word"
   Deferred word called before the text interpreter parses the next word

'line-end-hook' ( --  ) gforth-0.7 "line-end-hook"
   called at every end-of-line when text-interpreting from a file

6.15 The Input Stream
=====================

The text interpreter reads from the input stream, which can come from
several sources (*note Input Sources::).  Some words, in particular
defining words, but also words like ''', read parameters from the input
stream instead of from the stack.

   Such words are called parsing words, because they parse the input
stream.  Parsing words are hard to use in other words, because it is
hard to pass program-generated parameters through the input stream.
They also usually have an unintuitive combination of interpretation and
compilation semantics when implemented naively, leading to various
approaches that try to produce a more intuitive behaviour (*note
Combined words::).

   It should be obvious by now that parsing words are a bad idea.  If
you want to implement a parsing word for convenience, also provide a
factor of the word that does not parse, but takes the parameters on the
stack.  To implement the parsing word on top if it, you can use the
following words:

'parse' ( xchar "ccc<xchar>" -- c-addr u  ) core-ext,xchar-ext "parse"
   Parse ccc, delimited by xchar, in the parse area.  c-addr u specifies
the parsed string within the parse area.  If the parse area was empty, u
is 0.

'string-parse' ( c-addr1 u1 "ccc<string>" -- c-addr2 u2  ) gforth-1.0 "string-parse"
   Parse ccc, delimited by the string c-addr1 u1, in the parse area.
c-addr2 u2 specifies the parsed string within the parse area.  If the
parse area was empty, u2 is 0.

'parse-name' ( "name" -- c-addr u  ) core-ext "parse-name"
   Get the next word from the input buffer

'parse-word' ( -- c-addr u  ) gforth-obsolete "parse-word"
   old name for 'parse-name'; this word has a conflicting behaviour in
some other systems.

'name' ( -- c-addr u  ) gforth-obsolete "name"
   old name for 'parse-name'

'word' ( char "<chars>ccc<char>-- c-addr  ) core "word"
   Skip leading delimiters.  Parse ccc, delimited by char, in the parse
area.  c-addr is the address of a transient region containing the parsed
string in counted-string format.  If the parse area was empty or
contained no characters other than delimiters, the resulting string has
zero length.  A program may replace characters within the counted
string.  OBSOLESCENT: the counted string has a trailing space that is
not included in its length.

'refill' ( -- flag  ) core-ext,block-ext,file-ext "refill"
   Attempt to fill the input buffer from the input source.  When the
input source is the user input device, attempt to receive input into the
terminal input device.  If successful, make the result the input buffer,
set '>IN' to 0 and return true; otherwise return false.  When the input
source is a block, add 1 to the value of 'BLK' to make the next block
the input source and current input buffer, and set '>IN' to 0; return
true if the new value of 'BLK' is a valid block number, false otherwise.
When the input source is a text file, attempt to read the next line from
the file.  If successful, make the result the current input buffer, set
'>IN' to 0 and return true; otherwise, return false.  A successful
result includes receipt of a line containing 0 characters.

   If you have to deal with a parsing word that does not have a
non-parsing factor, you can use 'execute-parsing' to pass a string to
it:

'execute-parsing' ( ... addr u xt -- ...  ) gforth-0.6 "execute-parsing"
   Make addr u the current input source, execute xt '( ... -- ... )',
then restore the previous input source.

   Example:

     5 s" foo" ' constant execute-parsing
     \ equivalent to
     5 constant foo

   A definition of this word in Standard Forth is provided in
'compat/execute-parsing.fs'.

   If you want to run a parsing word on a file, the following word
should help:

'execute-parsing-file' ( i*x fileid xt -- j*x  ) gforth-0.6 "execute-parsing-file"
   Make fileid the current input source, execute xt '( i*x -- j*x )',
then restore the previous input source.

6.16 Word Lists
===============

A wordlist is a list of named words; you can add new words and look up
words by name (and you can remove words in a restricted way with
markers).  Every named (and 'reveal'ed) word is in one wordlist.

   The text interpreter searches the wordlists present in the search
order (a stack of wordlists), from the top to the bottom.  Within each
wordlist, the search starts conceptually at the newest word; i.e., if
two words in a wordlist have the same name, the newer word is found.

   New words are added to the "compilation wordlist" (aka current
wordlist).

   A word list is identified by a cell-sized word list identifier (wid)
in much the same way as a file is identified by a file handle.  The
numerical value of the wid has no (portable) meaning, and might change
from session to session.

   The Standard Forth "Search order" word set is intended to provide a
set of low-level tools that allow various different schemes to be
implemented.  Gforth also provides 'vocabulary', a traditional Forth
word.  'compat/vocabulary.fs' provides an implementation in Standard
Forth.

'forth-wordlist' ( -- wid  ) search "forth-wordlist"
   'Constant' -- wid identifies the word list that includes all of the
standard words provided by Gforth.  When Gforth is invoked, this word
list is the compilation word list and is at the top of the search order.

'definitions' ( --  ) search "definitions"
   Set the compilation word list to be the same as the word list that is
currently at the top of the search order.

'get-current' ( -- wid  ) search "get-current"
   wid is the identifier of the current compilation word list.

'set-current' ( wid --  ) search "set-current"
   Set the compilation word list to the word list identified by wid.

'get-order' ( -- widn .. wid1 n  ) search "get-order"
   Copy the search order to the data stack.  The current search order
has n entries, of which wid1 represents the wordlist that is searched
first (the word list at the top of the search order) and widn represents
the wordlist that is searched last.

'set-order' ( widn .. wid1 n --  ) search "set-order"
   If N=0, empty the search order.  If N=-1, set the search order to the
implementation-defined minimum search order (for Gforth, this is the
word list 'Root').  Otherwise, replace the existing search order with
the N wid entries such that WID1 represents the word list that will be
searched first and WIDN represents the word list that will be searched
last.

'wordlist' ( -- wid  ) search "wordlist"
   Create a new, empty word list represented by wid.

'table' ( -- wid  ) gforth-0.2 "table"
   Create a lookup table (case-sensitive, no warnings).

'cs-wordlist' ( -- wid  ) gforth-1.0 "cs-wordlist"
   Create a case-sensitive wordlist.

'cs-vocabulary' ( "name" --  ) gforth-1.0 "cs-vocabulary"
   Create a case-sensitive vocabulary

'>order' ( wid --  ) gforth-0.5 "to-order"
   Push WID on the search order.

'previous' ( --  ) search-ext "previous"
   Drop the wordlist at the top of the search order.

'also' ( --  ) search-ext "also"
   Like 'DUP' for the search order.  Usually used before a vocabulary
(e.g., 'also Forth'); the combined effect is to push the wordlist
represented by the vocabulary on the search order.

'Forth' ( --  ) search-ext "Forth"
   Replace the wid at the top of the search order with the wid
associated with the word list 'forth-wordlist'.

'Only' ( --  ) search-ext "Only"
   Set the search order to the implementation-defined minimum search
order (for Gforth, this is the word list 'Root').

'order' ( --  ) search-ext "order"
   Print the search order and the compilation word list.  The word lists
are printed in the order in which they are searched (which is reversed
with respect to the conventional way of displaying stacks).  The
compilation word list is displayed last.

'.voc' ( wid --  ) gforth-0.2 "dot-voc"
   print the name of the wordlist represented by WID.  Can only print
names defined with 'vocabulary' or 'wordlist constant', otherwise prints
'address'.

'find' ( c-addr -- xt +-1 | c-addr 0  ) core,search "find"
   Search all word lists in the current search order for the definition
named by the counted string at c-addr.  If the definition is not found,
return 0.  If the definition is found return 1 (if the definition has
non-default compilation semantics) or -1 (if the definition has default
compilation semantics).  The xt returned in interpret state represents
the interpretation semantics.  The xt returned in compile state
represented either the compilation semantics (for non-default
compilation semantics) or the run-time semantics that the compilation
semantics would 'compile,' (for default compilation semantics).  The ANS
Forth standard does not specify clearly what the returned xt represents
(and also talks about immediacy instead of non-default compilation
semantics), so this word is questionable in portable programs.  If
non-portability is ok, 'find-name' and friends are better (*note Name
token::).

'search-wordlist' ( c-addr count wid -- 0 | xt +-1  ) search "search-wordlist"
   Search the word list identified by wid for the definition named by
the string at c-addr count.  If the definition is not found, return 0.
If the definition is found return 1 (if the definition is immediate) or
-1 (if the definition is not immediate) together with the xt.  In
Gforth, the xt returned represents the interpretation semantics.  ANS
Forth does not specify clearly what xt represents.

'words' ( --  ) tools "words"
   Display a list of all of the definitions in the word list at the top
of the search order.

'vlist' ( --  ) gforth-0.2 "vlist"
   Old (pre-Forth-83) name for 'WORDS'.

'wordlist-words' ( wid --  ) gforth-0.6 "wordlist-words"
   Display the contents of the wordlist wid.

'mwords' ( ["pattern"] --  ) gforth-1.0 "mwords"
   list all words matching the optional parameter PATTERN; if none, all
words match.  Words are listed old to new.  Pattern match like 'search'
(default), you can switch to globbing with '' mword-filename-match is
mword-match'.

'Root' ( --  ) gforth-0.2 "Root"
   Add the root wordlist to the search order stack.  This vocabulary
makes up the minimum search order and contains only a search-order
words.

'Vocabulary' ( "name" --  ) gforth-0.2 "Vocabulary"
   Create a definition "name" and associate a new word list with it.
The run-time effect of "name" is to replace the wid at the top of the
search order with the wid associated with the new word list.

'seal' ( --  ) gforth-0.2 "seal"
   Remove all word lists from the search order stack other than the word
list that is currently on the top of the search order stack.

'vocs' ( --  ) gforth-0.2 "vocs"
   List vocabularies and wordlists defined in the system.

'current' ( -- addr  ) gforth-0.2 "current"
   'Variable' -- holds the wid of the compilation word list.

'context' ( -- addr  ) gforth-0.2 "context"
   'context' '@' is the wid of the word list at the top of the search
order.

'map-vocs' ( ... xt -- ...  ) gforth-1.0 "map-vocs"
   Perform xt ( ...  wid -- ...  )  for all wordlists (including tables
and cs-wordlists) in the system.

6.16.1 Vocabularies
-------------------

Here is an example of creating and using a new wordlist using Standard
Forth words:

     wordlist constant my-new-words-wordlist
     : my-new-words get-order nip my-new-words-wordlist swap set-order ;

     \ add it to the search order
     also my-new-words

     \ alternatively, add it to the search order and make it
     \ the compilation word list
     also my-new-words definitions
     \ type "order" to see the problem

   The problem with this example is that 'order' has no way to associate
the name 'my-new-words' with the wid of the word list (in Gforth,
'order' and 'vocs' will display '???' for a wid that has no associated
name).  There is no Standard way of associating a name with a wid.

   In Gforth, this example can be re-coded using 'vocabulary', which
associates a name with a wid:

     vocabulary my-new-words

     \ add it to the search order
     also my-new-words

     \ alternatively, add it to the search order and make it
     \ the compilation word list
     my-new-words definitions
     \ type "order" to see that the problem is solved

6.16.2 Why use word lists?
--------------------------

Here are some reasons why people use wordlists:

   * To prevent a set of words from being used outside the context in
     which they are valid.  Two classic examples of this are an
     integrated editor (all of the edit commands are defined in a
     separate word list; the search order is set to the editor word list
     when the editor is invoked; the old search order is restored when
     the editor is terminated) and an integrated assembler (the op-codes
     for the machine are defined in a separate word list which is used
     when a 'CODE' word is defined).

   * To organize the words of an application or library into a
     user-visible set (in 'forth-wordlist' or some other common
     wordlist) and a set of helper words used just for the
     implementation (hidden in a separate wordlist).  This keeps
     'words'' output smaller, separates implementation and interface,
     and reduces the chance of name conflicts within the common
     wordlist.

   * To prevent a name-space clash between multiple definitions with the
     same name.  For example, when building a cross-compiler you might
     have a word 'IF' that generates conditional code for your target
     system.  By placing this definition in a different word list you
     can control whether the host system's 'IF' or the target system's
     'IF' get used in any particular context by controlling the order of
     the word lists on the search order stack.

   The downsides of using wordlists are:

   * Debugging becomes more cumbersome.

   * Name conflicts worked around with wordlists are still there, and
     you have to arrange the search order carefully to get the desired
     results; if you forget to do that, you get hard-to-find errors (as
     in any case where you read the code differently from the compiler;
     'see' can help seeing which of several possible words the name
     resolves to in such cases).  'See' displays just the name of the
     words, not what wordlist they belong to, so it might be misleading.
     Using unique names is a better approach to avoid name conflicts.

   * You have to explicitly undo any changes to the search order.  In
     many cases it would be more convenient if this happened implicitly.
     Gforth currently does not provide such a feature, but it may do so
     in the future.

6.16.3 Word list example
------------------------

The following example is from the garbage collector
(https://www.complang.tuwien.ac.at/forth/garbage-collection.zip) and
uses wordlists to separate public words from helper words:

     get-current ( wid )
     vocabulary garbage-collector also garbage-collector definitions
     ... \ define helper words
     ( wid ) set-current \ restore original (i.e., public) compilation wordlist
     ... \ define the public (i.e., API) words
         \ they can refer to the helper words
     previous \ restore original search order (helper words become invisible)

6.17 Environmental Queries
==========================

Forth-94 introduced the idea of "environmental queries" as a way for a
program running on a system to determine certain characteristics of the
system.  The Standard specifies a number of strings that might be
recognised by a system, and a way of querying them:

'environment?' ( c-addr u -- false / ... true  ) core "environment-query"
   c-addr, u specify a counted string.  If the string is not recognised,
return a 'false' flag.  Otherwise return a 'true' flag and some
(string-specific) information about the queried string.

   Note that, whilst the documentation for (e.g.)  'ADDRESS-UNIT-BITS'
shows it returning one cell on the stack, querying it using
'environment?' will return an additional item; the 'true' flag that
shows that the string was recognised; so for querying
'ADDRESS-UNIT-BITS' the stack effect of 'environment?' is '( c-addr u --
n true )'.

   Several environmental queries deal with the system's limits:

'ADDRESS-UNIT-BITS' ( -- n  ) environment "ADDRESS-UNIT-BITS"
   Size of one address unit, in bits.

'MAX-CHAR' ( -- u  ) environment "MAX-CHAR"
   Maximum value of any character in the character set

'/COUNTED-STRING' ( -- n  ) environment "slash-counted-string"
   Maximum size of a counted string, in characters.

'/HOLD' ( -- n  ) environment "slash-hold"
   Size of the pictured numeric string output buffer, in characters.

'/PAD' ( -- n  ) environment "slash-pad"
   Size of the scratch area pointed to by 'PAD', in characters.

'CORE' ( -- f  ) environment "CORE"
   True if the complete core word set is present.  Always true for
Gforth.

'CORE-EXT' ( -- f  ) environment "CORE-EXT"
   True if the complete core extension word set is present.  Always true
for Gforth.

'FLOORED' ( -- f  ) environment "FLOORED"
   True if '/' etc.  perform floored division

'MAX-N' ( -- n  ) environment "MAX-N"
   Largest usable signed integer.

'MAX-U' ( -- u  ) environment "MAX-U"
   Largest usable unsigned integer.

'MAX-D' ( -- d  ) environment "MAX-D"
   Largest usable signed double.

'MAX-UD' ( -- ud  ) environment "MAX-UD"
   Largest usable unsigned double.

'return-stack-cells' ( -- n  ) environment "return-stack-cells"
   Maximum size of the return stack, in cells.

'stack-cells' ( -- n  ) environment "stack-cells"
   Maximum size of the data stack, in cells.

'floating-stack' ( -- n  ) environment "floating-stack"
   N is non-zero, showing that Gforth maintains a separate
floating-point stack of depth N.

'#locals' ( -- n  ) environment "number-locals"
   The maximum number of locals in a definition

'wordlists' ( -- n  ) environment "wordlists"
   the maximum number of wordlists usable in the search order

'max-float' ( -- r  ) environment "max-float"
   The largest usable floating-point number (implemented as largest
finite number in Gforth)

'XCHAR-ENCODING' ( -- addr u  ) environment "XCHAR-ENCODING"
   Returns a printable ASCII string that reperesents the encoding, and
use the preferred MIME name (if any) or the name in
<http://www.iana.org/assignments/character-sets> like "ISO-LATIN-1" or
"UTF-8", with the exception of "ASCII", where we prefer the alias
"ASCII".

'MAX-XCHAR' ( -- xchar  ) environment "MAX-XCHAR"
   Maximal value for xchar.  This depends on the encoding.

'XCHAR-MAXMEM' ( -- u  ) environment "XCHAR-MAXMEM"
   Maximal memory consumed by an xchar in address units

   Several environemtal queries are there for determining the presence
of the Forth-94 version of a wordset; they all have the stack effect '(
-- f )' if the string is present (so the 'environment?' stack effect for
these queries is '( c-addr u -- false / f true )'.

   'block block-ext double double-ext exception exception-ext facility
facility-ext file file-ext floating floating-ext locals locals-ext
memory-alloc memory-alloc-ext tools tools-ext search-order
search-order-ext string string-ext'

   These wordset queries were rarely used and implemented, so Forth-2012
did not introduce a way to query for the Forth-2012 variants of the
wordsets.  Instead, the idea is that you use '[defined]' (*note
Interpreter Directives::) instead.

   Forth-200x (a group that works on the next standard; the documents
that they produce are also called Forth-200x) defines extension queries
for the extension proposals once they finish changing (CfV stage), so
programs using these proposals can check whether a system has them, and
maybe load the reference implementation (if one exists).  If
'environment?' finds such a query, then the corresponding proposal on
<www.forth200x.org> is implemented on the system (but the absence tells
you nothing, as usual with 'environment?').  These queries have the
stack effect '( -- )', which means that for them 'environment?' has the
stack effect '( c-addr u -- false / true )', which is more convenient
than that of wordset queries.  A number of these proposals have been
incorporated into Forth-2012.  The extension queries are also not
particularly popular among Forth system implementors, so going for
'[defined]' may be the better approach.  Anyway, Gforth implements the
following extension queries:

   'X:2value X:buffer X:deferred X:defined X:ekeys X:escaped-strings
X:extension-query X:fp-stack X:ftrunc X:fvalue X:locals X:n-to-r
X:number-prefixes X:parse-name X:required X:s-escape-quote X:s-to-f
X:structures X:synonym X:text-substitution X:throw-iors
X:traverse-wordlist X:xchar'

   In addition, Gforth implements the following Gforth-specific queries:

'gforth' ( -- c-addr u  ) gforth-environment "gforth"
   Counted string representing a version string for this version of
Gforth (for versions>0.3.0).  The version strings of the various
versions are guaranteed to be ordered lexicographically.

'os-class' ( -- c-addr u  ) gforth-environment "os-class"
   Counted string representing a description of the host operating
system.

'os-type' ( -- c-addr u  ) gforth-environment "os-type"
   Counted string equal to "$host_os"

   The Standard requires that the header space used for environmental
queries be distinct from the header space used for definitions.

   Typically, a Forth system supports environmental queries by creating
a set of definitions in a wordlist that is only used for environmental
queries; that is what Gforth does.  There is no Standard way of adding
definitions to the set of recognised environmental queries, but in
Gforth and other systems that use the wordlist mechanism, the wordlist
used to honour environmental queries can be manipulated just like any
other word list.

'environment-wordlist' ( -- wid  ) gforth-0.2 "environment-wordlist"
   wid identifies the word list that is searched by environmental
queries (present in SwiftForth and VFX).

'environment' ( --  ) gforth-0.6 "environment"
   A vocabulary for 'environment-wordlist' (present in Win32Forth and
VFX).

   Here are some examples of using environmental queries:

     s" address-unit-bits" environment? 0=
     [IF]
          cr .( environmental attribute address-units-bits unknown... ) cr
     [ELSE]
          drop \ ensure balanced stack effect
     [THEN]

     \ this might occur in the prelude of a standard program that uses THROW
     s" exception" environment? [IF]
        0= [IF]
           : throw abort" exception thrown" ;
        [THEN]
     [ELSE] \ we don't know, so make sure
        : throw abort" exception thrown" ;
     [THEN]

     s" gforth" environment? [IF] .( Gforth version ) TYPE
                             [ELSE] .( Not Gforth..) [THEN]

     \ a program using v*
     s" gforth" environment? [IF]
       s" 0.5.0" compare 0< [IF] \ v* is a primitive since 0.5.0
        : v* ( f_addr1 nstride1 f_addr2 nstride2 ucount -- r )
          >r swap 2swap swap 0e r> 0 ?DO
            dup f@ over + 2swap dup f@ f* f+ over + 2swap
          LOOP
          2drop 2drop ;
       [THEN]
     [ELSE] \
       : v* ( f_addr1 nstride1 f_addr2 nstride2 ucount -- r )
       ...
     [THEN]

   Here is an example of adding a definition to the environment word
list:

     get-current environment-wordlist set-current
     true constant block
     true constant block-ext
     set-current

   You can see what definitions are in the environment word list like
this:

     environment-wordlist wordlist-words

6.18 Files
==========

Gforth provides facilities for accessing files that are stored in the
host operating system's file-system.  Files that are processed by Gforth
can be divided into two categories:

   * Files that are processed by the Text Interpreter ("Forth source
     files").
   * Files that are processed by some other program ("general files").

6.18.1 Forth source files
-------------------------

The simplest way to interpret the contents of a file is to use one of
these two formats:

     include mysource.fs
     s" mysource.fs" included

   You usually want to include a file only if it is not included already
(by, say, another source file).  In that case, you can use one of these
three formats:

     require mysource.fs
     needs mysource.fs
     s" mysource.fs" required

   It is good practice to write your source files such that interpreting
them does not change the stack.  Source files designed in this way can
be used with 'required' and friends without complications.  For example:

     1024 require foo.fs drop

   Here you want to pass the argument 1024 (e.g., a buffer size) to
'foo.fs'.  Interpreting 'foo.fs' has the stack effect ( n -- n ), which
allows its use with 'require'.  Of course with such parameters to
required files, you have to ensure that the first 'require' fits for all
uses (i.e., 'require' it early in the master load file).

'include-file' ( i*x wfileid -- j*x  ) file "include-file"
   Interpret (process using the text interpreter) the contents of the
file WFILEID.

'included' ( i*x c-addr u -- j*x  ) file "included"
   'include-file' the file whose name is given by the string C-ADDR U.

'included?' ( c-addr u -- f  ) gforth-0.2 "included?"
   True only if the file C-ADDR U is in the list of earlier included
files.  If the file has been loaded, it may have been specified as, say,
'foo.fs' and found somewhere on the Forth search path.  To return 'true'
from 'included?', you must specify the exact path to the file, even if
that is './foo.fs'

'include' ( ... "file" -- ...  ) file-ext "include"
   'include-file' the file FILE.

'required' ( i*x addr u -- i*x  ) file-ext "required"
   'include-file' the file with the name given by ADDR U, if it is not
'included' (or 'required') already.  Currently this works by comparing
the name of the file (with path) against the names of earlier included
files.

'require' ( ... "file" -- ...  ) file-ext "require"
   'include-file' FILE only if it is not included already.

'needs' ( ... "name" -- ...  ) gforth-0.2 "needs"
   An alias for 'require'; exists on other systems (e.g., Win32Forth).

'\\\' ( --  ) gforth-1.0 "\\\"
   skip remaining source file

'.included' ( --  ) gforth-0.5 ".included"
   List the names of the files that have been 'included'.

'sourcefilename' ( -- c-addr u  ) gforth-0.2 "sourcefilename"
   The name of the source file which is currently the input source.  The
result is valid only while the file is being loaded.  If the current
input source is no (stream) file, the result is undefined.  In Gforth,
the result is valid during the whole session (but not across
'savesystem' etc.).

'sourceline#' ( -- u  ) gforth-0.2 "sourceline-number"
   The line number of the line that is currently being interpreted from
a (stream) file.  The first line has the number 1.  If the current input
source is not a (stream) file, the result is undefined.

   A definition in Standard Forth for 'required' is provided in
'compat/required.fs'.

6.18.2 General files
--------------------

Files are opened/created by name and type.  The following file access
methods (FAMs) are recognised:

'r/o' ( -- fam  ) file "r-o"

'r/w' ( -- fam  ) file "r-w"

'w/o' ( -- fam  ) file "w-o"

'bin' ( fam1 -- fam2  ) file "bin"

'+fmode' ( fam1 rwxrwxrwx -- fam2  ) gforth-1.0 "plus-f-mode"
   add file access mode to fam - for create-file only

   When a file is opened/created, it returns a file identifier, wfileid
that is used for all other file commands.  All file commands also return
a status value, wior, that is 0 for a successful operation and an
implementation-defined non-zero value in the case of an error.

'open-file' ( c-addr u wfam -- wfileid wior ) file "open-file"

'create-file' ( c-addr u wfam -- wfileid wior ) file "create-file"

'close-file' ( wfileid -- wior ) file "close-file"

'delete-file' ( c-addr u -- wior ) file "delete-file"

'rename-file' ( c-addr1 u1 c-addr2 u2 -- wior ) file-ext "rename-file"
   Rename file c_addr1 u1 to new name c_addr2 u2

'read-file' ( c-addr u1 wfileid -- u2 wior ) file "read-file"
   Read u1 characters from file wfileid into the buffer at c_addr.  A
non-zero wior indicates an error.  U2 indicates the length of the read
data.  End-of-file is not an error and is indicated by u2$<$u1 and
wior=0.

'read-line' ( c_addr u1 wfileid -- u2 flag wior  ) file "read-line"
   Reads a line from wfileid into the buffer at c_addr u1.  Gforth
supports all three common line terminators: LF, CR and CRLF. A non-zero
wior indicates an error.  A false flag indicates that 'read-line' has
been invoked at the end of the file.  u2 indicates the line length
(without terminator): u2$<$u1 indicates that the line is u2 chars long;
u2=u1 indicates that the line is at least u1 chars long, the u1 chars of
the buffer have been filled with chars from the line, and the next slice
of the line with be read with the next 'read-line'.  If the line is u1
chars long, the first 'read-line' returns u2=u1 and the next read-line
returns u2=0.

'key-file' ( fd -- key  ) gforth-0.4 "key-file"
   Read one character n from wfileid.  This word disables buffering for
wfileid.  If you want to read characters from a terminal in
non-canonical (raw) mode, you have to put the terminal in non-canonical
mode yourself (using the C interface); the exception is 'stdin': Gforth
automatically puts it into non-canonical mode.

'key?-file' ( wfileid -- f ) gforth-0.4 "key-q-file"
   f is true if at least one character can be read from wfileid without
blocking.  If you also want to use 'read-file' or 'read-line' on the
file, you have to call 'key?-file' or 'key-file' first (these two words
disable buffering).

'file-eof?' ( wfileid -- flag ) gforth-0.6 "file-eof-query"
   FLAG is true if the end-of-file indicator for WFILEID is set.

'write-file' ( c-addr u1 wfileid -- wior ) file "write-file"

'write-line' ( c-addr u wfileid -- ior  ) file "write-line"

'emit-file' ( c wfileid -- wior ) gforth-0.2 "emit-file"

'flush-file' ( wfileid -- wior ) file-ext "flush-file"

'file-status' ( c-addr u -- wfam wior ) file-ext "file-status"

'file-position' ( wfileid -- ud wior ) file "file-position"

'reposition-file' ( ud wfileid -- wior ) file "reposition-file"

'file-size' ( wfileid -- ud wior ) file "file-size"

'resize-file' ( ud wfileid -- wior ) file "resize-file"

'slurp-file' ( c-addr1 u1 -- c-addr2 u2  ) gforth-0.6 "slurp-file"
   C-ADDR1 U1 is the filename, C-ADDR2 U2 is the file's contents

'slurp-fid' ( fid -- addr u  ) gforth-0.6 "slurp-fid"
   ADDR U is the content of the file FID

'stdin' ( -- wfileid ) gforth-0.4 "stdin"
   The standard input file of the Gforth process.

'stdout' ( -- wfileid ) gforth-0.2 "stdout"
   The standard output file of the Gforth process.

'stderr' ( -- wfileid ) gforth-0.2 "stderr"
   The standard error output file of the Gforth process.

6.18.3 Redirection
------------------

You can redirect the output of 'type' and 'emit' and all the words that
use them (all output words that don't have an explicit target file) to
an arbitrary file with the 'outfile-execute', used like this:

     : some-warning ( n -- )
         cr ." warning# " . ;

     : print-some-warning ( n -- )
         ['] some-warning stderr outfile-execute ;

   After 'some-warning' is executed, the original output direction is
restored; this construct is safe against exceptions.  Similarly, there
is 'infile-execute' for redirecting the input of 'key' and its users
(any input word that does not take a file explicitly).

'outfile-execute' ( ... xt file-id -- ...  ) gforth-0.7 "outfile-execute"
   execute xt with the output of 'type' etc.  redirected to file-id.

'outfile-id' ( -- file-id  ) gforth-0.2 "outfile-id"
   File-id is used by 'emit', 'type', and any output word that does not
take a file-id as input.  By default 'outfile-id' produces the process's
'stdout', unless changed with 'outfile-execute'.

'infile-execute' ( ... xt file-id -- ...  ) gforth-0.7 "infile-execute"
   execute xt with the input of 'key' etc.  redirected to file-id.

'infile-id' ( -- file-id  ) gforth-0.4 "infile-id"
   File-id is used by 'key', '?key', and anything that refers to the
"user input device".  By default 'infile-id' produces the process's
'stdin', unless changed with 'infile-execute'.

   If you do not want to redirect the input or output to a file, you can
also make use of the fact that 'key', 'emit' and 'type' are deferred
words (*note Deferred Words::).  However, in that case you have to worry
about the restoration and the protection against exceptions yourself;
also, note that for redirecting the output in this way, you have to
redirect both 'emit' and 'type'.

6.18.4 Directories
------------------

You can split a file name into a directory and base component:

'basename' ( c-addr1 u1 -- c-addr2 u2  ) gforth-0.7 "basename"
   Given a file name c-addr1 u1, c-addr2 u2 is the part of it with any
leading directory components removed.

'dirname' ( c-addr1 u1 -- c-addr1 u2  ) gforth-0.7 "dirname"
   C-addr1 u2 is the directory name of the file name c-addr1 u1,
including the final '/'.  If caddr1 u1 does not contain a '/', u2=0.

   You can open and read directories similar to files.  Reading gives
you one directory entry at a time; you can match that to a filename
(with wildcards).

'open-dir' ( c-addr u -- wdirid wior ) gforth-0.5 "open-dir"
   Open the directory specified by c-addr, u and return dir-id for
futher access to it.

'read-dir' ( c-addr u1 wdirid -- u2 flag wior ) gforth-0.5 "read-dir"
   Attempt to read the next entry from the directory specified by dir-id
to the buffer of length u1 at address c-addr.  If the attempt fails
because there is no more entries, ior=0, flag=0, u2=0, and the buffer is
unmodified.  If the attempt to read the next entry fails because of any
other reason, return ior<>0.  If the attempt succeeds, store file name
to the buffer at c-addr and return ior=0, flag=true and u2 equal to the
size of the file name.  If the length of the file name is greater than
u1, store first u1 characters from file name into the buffer and
indicate "name too long" with ior, flag=true, and u2=u1.

'close-dir' ( wdirid -- wior ) gforth-0.5 "close-dir"
   Close the directory specified by dir-id.

'filename-match' ( c-addr1 u1 c-addr2 u2 -- flag ) gforth-0.5 "match-file"
   match the file name C_ADDR1 U1 with the pattern C_ADDR2 U2.  Patterns
match char by char except for the special characters '*' and '?', which
are wildcards for several ('*') or one ('?') character.

'get-dir' ( c-addr1 u1 -- c-addr2 u2 ) gforth-0.7 "get-dir"
   Store the current directory in the buffer specified by c-addr1, u1.
If the buffer size is not sufficient, return 0 0

'set-dir' ( c-addr u -- wior ) gforth-0.7 "set-dir"
   Change the current directory to c-addr, u.  Return an error if this
is not possible

'=mkdir' ( c-addr u wmode -- wior ) gforth-0.7 "equals-mkdir"
   Create directory c-addr u with mode wmode.

'mkdir-parents' ( c-addr u mode -- ior  ) gforth-0.7 "mkdir-parents"
   create the directory c-addr u and all its parents with mode mode
(modified by umask)

6.18.5 Search Paths
-------------------

If you specify an absolute filename (i.e., a filename starting with '/'
or '~', or with ':' in the second position (as in 'C:...')) for
'included' and friends, that file is included just as you would expect.

   If the filename starts with './', this refers to the directory that
the present file was 'included' from.  This allows files to include
other files relative to their own position (irrespective of the current
working directory or the absolute position).  This feature is essential
for libraries consisting of several files, where a file may include
other files from the library.  It corresponds to '#include "..."' in C.
If the current input source is not a file, '.' refers to the directory
of the innermost file being included, or, if there is no file being
included, to the current working directory.

   For relative filenames (not starting with './'), Gforth uses a search
path similar to Forth's search order (*note Word Lists::).  It tries to
find the given filename in the directories present in the path, and
includes the first one it finds.  There are separate search paths for
Forth source files and general files.  If the search path contains the
directory '.', this refers to the directory of the current file, or the
working directory, as if the file had been specified with './'.

   Use '~+' to refer to the current working directory (as in the
'bash').

'absolute-file?' ( addr u -- flag  ) gforth-1.0 "absolute-file?"
   A filename is absolute if it starts with a / or a ~ (~ expansion), or
if it is in the form ./*, extended regexp: ^[/~]|./, or if it has a
colon as second character ("C:...").  Paths simply containing a / are
not absolute!

6.18.5.1 Source Search Paths
............................

The search path is initialized when you start Gforth (*note Invoking
Gforth::).  You can display it and change it using 'fpath' in
combination with the general path handling words.

'fpath' ( -- path-addr  ) gforth-0.4 "fpath"

'.fpath' ( --  ) gforth-0.4 ".fpath"
   Display the contents of the Forth search path.

'file>fpath' ( addr1 u1 -- addr2 u2  ) gforth-1.0 "file>fpath"
   Searches for a file with the name c-addr1 u1 in the 'fpath'.  If
successful, c-addr u2 is the absolute file name or the file name
relative to the current working directory.  Throws an exception if the
file cannot be opened.

Here is an example of using 'fpath' and 'require':

     fpath path= /usr/lib/forth/|./
     require timer.fs

6.18.5.2 General Search Paths
.............................

Your application may need to search files in several directories, like
'included' does.  To facilitate this, Gforth allows you to define and
use your own search paths, by providing generic equivalents of the Forth
search path words:

'open-path-file' ( addr1 u1 path-addr -- wfileid addr2 u2 0 | ior  ) gforth-0.2 "open-path-file"
   Look in path PATH-ADDR for the file specified by ADDR1 U1.  If found,
the resulting path and an (read-only) open file descriptor are returned.
If the file is not found, IOR is what came back from the last attempt at
opening the file (in the current implementation).

'file>path' ( c-addr1 u1 path-addr -- c-addr2 u2  ) gforth-1.0 "file>path"
   Searches for a file with the name c-addr1 u1 in path stored in
path-addr.  If successful, c-addr u2 is the absolute file name or the
file name relative to the current working directory.  Throws an
exception if the file cannot be opened.

'clear-path' ( path-addr --  ) gforth-0.5 "clear-path"
   Set the path path-addr to empty.

'also-path' ( c-addr len path-addr --  ) gforth-0.4 "also-path"
   add the directory c-addr len to path-addr.

'.path' ( path-addr --  ) gforth-0.4 ".path"
   Display the contents of the search path PATH-ADDR.

'path+' ( path-addr  "dir" --  ) gforth-0.4 "path+"
   Add the directory DIR to the search path PATH-ADDR.

'path=' ( path-addr "dir1|dir2|dir3" --  ) gforth-0.4 "path-equals"
   Make a complete new search path; the path separator is |.

   Here's an example of creating a custom search path:
     variable mypath \ no special allocation required, just a variable
     mypath path= /lib|/usr/lib \ assign initial directories
     mypath path+ /usr/local/lib \ append directory
     mypath .path \ output:"/lib /usr/lib /usr/local/lib"

   Search file and show resulting path:
     s" libm.so" mypath open-path-file throw type close-file \ output:"/lib/libm.so"

6.19 Blocks
===========

When you run Gforth on a modern desk-top computer, it runs under the
control of an operating system which provides certain services.  One of
these services is FILE SERVICES, which allows Forth source code and data
to be stored in files and read into Gforth (*note Files::).

   Traditionally, Forth has been an important programming language on
systems where it has interfaced directly to the underlying hardware with
no intervening operating system.  Forth provides a mechanism, called
"blocks", for accessing mass storage on such systems.

   A block is a 1024-byte data area, which can be used to hold data or
Forth source code.  No structure is imposed on the contents of the
block.  A block is identified by its number; blocks are numbered
contiguously from 1 to an implementation-defined maximum.

   A typical system that used blocks but no operating system might use a
single floppy-disk drive for mass storage, with the disks formatted to
provide 256-byte sectors.  Blocks would be implemented by assigning the
first four sectors of the disk to block 1, the second four sectors to
block 2 and so on, up to the limit of the capacity of the disk.  The
disk would not contain any file system information, just the set of
blocks.

   On systems that do provide file services, blocks are typically
implemented by storing a sequence of blocks within a single "blocks
file".  The size of the blocks file will be an exact multiple of 1024
bytes, corresponding to the number of blocks it contains.  This is the
mechanism that Gforth uses.

   Only one blocks file can be open at a time.  If you use block words
without having specified a blocks file, Gforth defaults to the blocks
file 'blocks.fb'.  Gforth uses the Forth search path when attempting to
locate a blocks file (*note Source Search Paths::).

   When you read and write blocks under program control, Gforth uses a
number of "block buffers" as intermediate storage.  These buffers are
not used when you use 'load' to interpret the contents of a block.

   The behaviour of the block buffers is analagous to that of a cache.
Each block buffer has three states:

   * Unassigned
   * Assigned-clean
   * Assigned-dirty

   Initially, all block buffers are unassigned.  In order to access a
block, the block (specified by its block number) must be assigned to a
block buffer.

   The assignment of a block to a block buffer is performed by 'block'
or 'buffer'.  Use 'block' when you wish to modify the existing contents
of a block.  Use 'buffer' when you don't care about the existing
contents of the block(1).

   Once a block has been assigned to a block buffer using 'block' or
'buffer', that block buffer becomes the current block buffer.  Data may
only be manipulated (read or written) within the current block buffer.

   When the contents of the current block buffer has been modified it is
necessary, _before calling 'block' or 'buffer' again_, to either abandon
the changes (by doing nothing) or mark the block as changed
(assigned-dirty), using 'update'.  Using 'update' does not change the
blocks file; it simply changes a block buffer's state to assigned-dirty.
The block will be written implicitly when it's buffer is needed for
another block, or explicitly by 'flush' or 'save-buffers'.

   word 'Flush' writes all assigned-dirty blocks back to the blocks file
on disk.  Leaving Gforth with 'bye' also performs a 'flush'.

   In Gforth, 'block' and 'buffer' use a direct-mapped algorithm to
assign a block buffer to a block.  That means that any particular block
can only be assigned to one specific block buffer, called (for the
particular operation) the victim buffer.  If the victim buffer is
unassigned or assigned-clean it is allocated to the new block
immediately.  If it is assigned-dirty its current contents are written
back to the blocks file on disk before it is allocated to the new block.

   Although no structure is imposed on the contents of a block, it is
traditional to display the contents as 16 lines each of 64 characters.
A block provides a single, continuous stream of input (for example, it
acts as a single parse area) -- there are no end-of-line characters
within a block, and no end-of-file character at the end of a block.
There are two consequences of this:

   * The last character of one line wraps straight into the first
     character of the following line
   * The word '\' -- comment to end of line -- requires special treatment;
     in the context of a block it causes all characters until the end of
     the current 64-character "line" to be ignored.

   In Gforth, when you use 'block' with a non-existent block number, the
current blocks file will be extended to the appropriate size and the
block buffer will be initialised with spaces.

   Gforth includes a simple block editor (type 'use blocked.fb 0 list'
for details) but doesn't encourage the use of blocks; the mechanism is
only provided for backward compatibility.

   Common techniques that are used when working with blocks include:

   * A screen editor that allows you to edit blocks without leaving the
     Forth environment.
   * Shadow screens; where every code block has an associated block
     containing comments (for example: code in odd block numbers,
     comments in even block numbers).  Typically, the block editor
     provides a convenient mechanism to toggle between code and
     comments.
   * Load blocks; a single block (typically block 1) contains a number
     of 'thru' commands which 'load' the whole of the application.

   See Frank Sergeant's Pygmy Forth to see just how well blocks can be
integrated into a Forth programming environment.

'open-blocks' ( c-addr u --  ) gforth-0.2 "open-blocks"
   Use the file, whose name is given by c-addr u, as the blocks file.

'use' ( "file" --  ) gforth-0.2 "use"
   Use file as the blocks file.

'block-offset' ( -- addr  ) gforth-0.5 "block-offset"
   User variable containing the number of the first block (default since
0.5.0: 0).  Block files created with Gforth versions before 0.5.0 have
the offset 1.  If you use these files you can: '1 offset !'; or add 1 to
every block number used; or prepend 1024 characters to the file.

'get-block-fid' ( -- wfileid  ) gforth-0.2 "get-block-fid"
   Return the file-id of the current blocks file.  If no blocks file has
been opened, use 'blocks.fb' as the default blocks file.

'block-position' ( u --  ) block "block-position"
   Position the block file to the start of block u.

'list' ( u --  ) block-ext "list"
   Display block u.  In Gforth, the block is displayed as 16 numbered
lines, each of 64 characters.

'scr' ( -- a-addr  ) block-ext "s-c-r"
   'User' variable containing the block number of the block most
recently processed by 'list'.

'block' ( u -- a-addr  ) block "block"
   If a block buffer is assigned for block u, return its start address,
a-addr.  Otherwise, assign a block buffer for block u (if the assigned
block buffer has been 'update'd, transfer the contents to mass storage),
read the block into the block buffer and return its start address,
a-addr.

'buffer' ( u -- a-addr  ) block "buffer"
   If a block buffer is assigned for block u, return its start address,
a-addr.  Otherwise, assign a block buffer for block u (if the assigned
block buffer has been 'update'd, transfer the contents to mass storage)
and return its start address, a-addr.  The subtle difference between
'buffer' and 'block' mean that you should only use 'buffer' if you don't
care about the previous contents of block u.  In Gforth, this simply
calls 'block'.

'empty-buffers' ( --  ) block-ext "empty-buffers"
   Mark all block buffers as unassigned; if any had been marked as
assigned-dirty (by 'update'), the changes to those blocks will be lost.

'empty-buffer' ( buffer --  ) gforth-0.2 "empty-buffer"

'update' ( --  ) block "update"
   Mark the state of the current block buffer as assigned-dirty.

'updated?' ( n -- f  ) gforth-0.2 "updated?"
   Return true if 'updated' has been used to mark block n as
assigned-dirty.

'save-buffers' ( --  ) block "save-buffers"
   Transfer the contents of each 'update'd block buffer to mass storage,
then mark all block buffers as assigned-clean.

'save-buffer' ( buffer --  ) gforth-0.2 "save-buffer"

'flush' ( --  ) block "flush"
   Perform the functions of 'save-buffers' then 'empty-buffers'.

'load' ( i*x u -- j*x  ) block "load"
   Text-interpret block u.  Block 0 cannot be 'load'ed.

'thru' ( i*x n1 n2 -- j*x  ) block-ext "thru"
   'load' the blocks n1 through n2 in sequence.

'+load' ( i*x n -- j*x  ) gforth-0.2 "+load"
   Used within a block to load the block specified as the current block
+ n.

'+thru' ( i*x n1 n2 -- j*x  ) gforth-0.2 "+thru"
   Used within a block to load the range of blocks specified as the
current block + n1 thru the current block + n2.

'-->' ( --  ) gforth-0.2 "chain"
   If this symbol is encountered whilst loading block n, discard the
remainder of the block and load block n+1.  Used for chaining multiple
blocks together as a single loadable unit.  Not recommended, because it
destroys the independence of loading.  Use 'thru' (which is standard) or
'+thru' instead.

'block-included' ( a-addr u --  ) gforth-0.2 "block-included"
   Use within a block that is to be processed by 'load'.  Save the
current blocks file specification, open the blocks file specified by
a-addr u and 'load' block 1 from that file (which may in turn chain or
load other blocks).  Finally, close the blocks file and restore the
original blocks file.

   ---------- Footnotes ----------

   (1) The Standard Forth definition of 'buffer' is intended not to
cause disk I/O; if the data associated with the particular block is
already stored in a block buffer due to an earlier 'block' command,
'buffer' will return that block buffer and the existing contents of the
block will be available.  Otherwise, 'buffer' will simply assign a new,
empty block buffer for the block.

6.20 Other I/O
==============

6.20.1 Simple numeric output
----------------------------

The simplest output functions are those that display numbers from the
data stack.  Numbers are displayed in the base (aka radix) stored in
'base' (*note Number Conversion::).

'.' ( n --  ) core "dot"
   Display (the signed single number) N in free-format, followed by a
space.

'dec.' ( n --  ) gforth-0.2 "dec."
   Display n as a signed decimal number, followed by a space.

   doc-hex.
'u.' ( u --  ) core "u-dot"
   Display (the unsigned single number) U in free-format, followed by a
space.

'.r' ( n1 n2 --  ) core-ext "dot-r"
   Display N1 right-aligned in a field N2 characters wide.  If more than
N2 characters are needed to display the number, all digits are
displayed.  If appropriate, N2 must include a character for a leading
"-".

'u.r' ( u n --  ) core-ext "u-dot-r"
   Display U right-aligned in a field N characters wide.  If more than N
characters are needed to display the number, all digits are displayed.

'dec.r' ( u n --  ) gforth-0.5 "dec.r"
   Display u as a unsigned decimal number in a field n characters wide.

'd.' ( d --  ) double "d-dot"
   Display (the signed double number) D in free-format.  followed by a
space.

'ud.' ( ud --  ) gforth-0.2 "u-d-dot"
   Display (the signed double number) UD in free-format, followed by a
space.

'd.r' ( d n --  ) double "d-dot-r"
   Display D right-aligned in a field N characters wide.  If more than N
characters are needed to display the number, all digits are displayed.
If appropriate, N must include a character for a leading "-".

'ud.r' ( ud n --  ) gforth-0.2 "u-d-dot-r"
   Display UD right-aligned in a field N characters wide.  If more than
N characters are needed to display the number, all digits are displayed.

6.20.2 Formatted numeric output
-------------------------------

Forth traditionally uses a technique called "pictured numeric output"
for formatted printing of integers.  In this technique, digits are
extracted from the number (using the current output radix defined by
'base', *note Number Conversion::), converted to ASCII codes and
prepended to a string that is built in a scratch-pad area of memory
(*note Implementation-defined options: core-idef.).  Arbitrary
characters can be prepended to the string during the extraction process.
The completed string is specified by an address and length and can be
manipulated ('TYPE'ed, copied, modified) under program control.

   All of the integer output words described in the previous section
(*note Simple numeric output::) are implemented in Gforth using pictured
numeric output.

   Three important things to remember about pictured numeric output:

   * It always operates on double-precision numbers; to display a
     single-precision number, convert it first (for ways of doing this
     *note Double precision::).
   * It always treats the double-precision number as though it were
     unsigned.  The examples below show ways of printing signed numbers.
   * The string is built up from right to left; least significant digit
     first.

   Standard Forth supports a single output buffer (aka hold area) that
you empty and initialize with '<#' and for which you get the result
string with '#>'.

   Gforth additionally supports nested usage of this buffer, allowing,
e.g., to nest output from the debugging tracer '~~' inside code dealing
with the hold area: '<<#' starts a new nest, '#>' produces the result
string, and '#>>' unnests: the hold area for the nest is reclaimed, and
'#>' now produces the string for the next-outer nest.  All of Gforth's
higher-level numeric output words use '<<#' ...  '#>' ...  '#>>' and can
be nested inside other users of the hold area.

'<#' ( --  ) core "less-number-sign"
   Initialise/clear the pictured numeric output string.

'<<#' ( --  ) gforth-0.5 "less-less-number-sign"
   Start a hold area that ends with '#>>'.  Can be nested in each other
and in '<#'.  Note: if you do not match up the '<<#'s with '#>>'s, you
will eventually run out of hold area; you can reset the hold area to
empty with '<#'.

'#' ( ud1 -- ud2  ) core "number-sign"
   Used between '<<#' and '#>'.  Prepend the least-significant digit
(according to 'base') of UD1 to the pictured numeric output string.  UD2
is UD1/BASE, i.e., the number representing the remaining digits.

'#s' ( ud -- 0 0  ) core "number-sign-s"
   Used between '<<#' and '#>'.  Prepend all digits of UD to the
pictured numeric output string.  '#s' will convert at least one digit.
Therefore, if UD is 0, '#s' will prepend a "0" to the pictured numeric
output string.

'hold' ( char --  ) core "hold"
   Used between '<<#' and '#>'.  Prepend the character CHAR to the
pictured numeric output string.

'holds' ( addr u --  ) core-ext "holds"
   Used between '<<#' and '#>'.  Prepend the string 'addr u' to the
pictured numeric output string.

'sign' ( n --  ) core "sign"
   Used between '<<#' and '#>'.  If N (a SINGLE number) is negative,
prepend "'-'" to the pictured numeric output string.

'#>' ( xd -- addr u  ) core "number-sign-greater"
   Complete the pictured numeric output string by discarding XD and
returning ADDR U; the address and length of the formatted string.  A
Standard program may modify characters within the string.  Does not
release the hold area; use '#>>' to release a hold area started with
'<<#', or '<#' to release all hold areas.

'#>>' ( --  ) gforth-0.5 "number-sign-greater-greater"
   Release the hold area started with '<<#'.

Here are some examples of using pictured numeric output:

     : my-u. ( u -- )
       \ Simplest use of pns.. behaves like Standard u.
       0              \ convert to unsigned double
       <<#            \ start conversion
       #s             \ convert all digits
       #>             \ complete conversion
       TYPE SPACE     \ display, with trailing space
       #>> ;          \ release hold area

     : cents-only ( u -- )
       0              \ convert to unsigned double
       <<#            \ start conversion
       # #            \ convert two least-significant digits
       #>             \ complete conversion, discard other digits
       TYPE SPACE     \ display, with trailing space
       #>> ;          \ release hold area

     : dollars-and-cents ( u -- )
       0              \ convert to unsigned double
       <<#            \ start conversion
       # #            \ convert two least-significant digits
       '.' hold       \ insert decimal point
       #s             \ convert remaining digits
       '$' hold       \ append currency symbol
       #>             \ complete conversion
       TYPE SPACE     \ display, with trailing space
       #>> ;          \ release hold area

     : my-. ( n -- )
       \ handling negatives.. behaves like Standard .
       s>d            \ convert to signed double
       swap over dabs \ leave sign byte followed by unsigned double
       <<#            \ start conversion
       #s             \ convert all digits
       rot sign       \ get at sign byte, append "-" if needed
       #>             \ complete conversion
       TYPE SPACE     \ display, with trailing space
       #>> ;          \ release hold area

     : account. ( n -- )
       \ accountants don't like minus signs, they use parentheses
       \ for negative numbers
       s>d            \ convert to signed double
       swap over dabs \ leave sign byte followed by unsigned double
       <<#            \ start conversion
       2 pick         \ get copy of sign byte
       0< IF ')' hold THEN \ right-most character of output
       #s             \ convert all digits
       rot            \ get at sign byte
       0< IF '(' hold THEN
       #>             \ complete conversion
       TYPE SPACE     \ display, with trailing space
       #>> ;          \ release hold area


   Here are some examples of using these words:

     1 my-u. 1
     hex -1 my-u. decimal FFFFFFFF
     1 cents-only 01
     1234 cents-only 34
     2 dollars-and-cents $0.02
     1234 dollars-and-cents $12.34
     123 my-. 123
     -123 my. -123
     123 account. 123
     -456 account. (456)

6.20.3 Floating-point output
----------------------------

Floating-point output is always displayed using base 10.

'f.' ( r --  ) floating-ext "f-dot"
   Display (the floating-point number) r without exponent, followed by a
space.

'fe.' ( r --  ) floating-ext "f-e-dot"
   Display r using engineering notation (with exponent dividable by 3),
followed by a space.

'fs.' ( r --  ) floating-ext "f-s-dot"
   Display r using scientific notation (with exponent), followed by a
space.

'fp.' ( r --  ) floating-ext "f-e-dot"
   Display r using SI prefix notation (with exponent dividable by 3,
converted into SI prefixes if available), followed by a space.

   Examples of printing the number 1234.5678E23 in the different
floating-point output formats are shown below.

     f. 123456780000000000000000000.
     fe. 123.456780000000E24
     fs. 1.23456780000000E26
     fp. 123.456780000000Y

   The length of the output is influenced by:

'precision' ( -- u  ) floating-ext "precision"
   u is the number of significant digits currently used by 'F.' 'FE.'
and 'FS.'

'set-precision' ( u --  ) floating-ext "set-precision"
   Set the number of significant digits currently used by 'F.' 'FE.' and
'FS.' to u.

   You can control the output in more detail with:

'f.rdp' ( rf +nr +nd +np --  ) gforth-0.6 "f.rdp"
   Print float rf formatted.  The total width of the output is nr.  For
fixed-point notation, the number of digits after the decimal point is
+nd and the minimum number of significant digits is np.  'Set-precision'
has no effect on 'f.rdp'.  Fixed-point notation is used if the number of
siginicant digits would be at least np and if the number of digits
before the decimal point would fit.  If fixed-point notation is not
used, exponential notation is used, and if that does not fit, asterisks
are printed.  We recommend using nr>=7 to avoid the risk of numbers not
fitting at all.  We recommend nr>=np+5 to avoid cases where 'f.rdp'
switches to exponential notation because fixed-point notation would have
too few significant digits, yet exponential notation offers fewer
significant digits.  We recommend nr>=nd+2, if you want to have
fixed-point notation for some numbers; the smaller the value of np, the
more cases are shown in fixed-point notation (cases where few or no
significant digits remain in fixed-point notation).  We recommend np>nr,
if you want to have exponential notation for all numbers.

   To give you a better intuition of how they influence the output, here
are some examples of parameter combinations; in each line the same
number is printed, in each column the same parameter combination is used
for printing:

         12 13 0    7 3 4   7 3 0   7 3 1   7 5 1   7 7 1   7 0 2  4 2 1
     |-1.234568E-6|-1.2E-6| -0.000|-1.2E-6|-1.2E-6|-1.2E-6|-1.2E-6|****|
     |-1.234568E-5|-1.2E-5| -0.000|-1.2E-5|-.00001|-1.2E-5|-1.2E-5|****|
     |-1.234568E-4|-1.2E-4| -0.000|-1.2E-4|-.00012|-1.2E-4|-1.2E-4|****|
     |-1.234568E-3|-1.2E-3| -0.001| -0.001|-.00123|-1.2E-3|-1.2E-3|****|
     |-1.234568E-2|-1.2E-2| -0.012| -0.012|-.01235|-1.2E-2|-1.2E-2|-.01|
     |-1.234568E-1|-1.2E-1| -0.123| -0.123|-.12346|-1.2E-1|-1.2E-1|-.12|
     |-1.2345679E0| -1.235| -1.235| -1.235|-1.23E0|-1.23E0|-1.23E0|-1E0|
     |-1.2345679E1|-12.346|-12.346|-12.346|-1.23E1|-1.23E1|   -12.|-1E1|
     |-1.2345679E2|-1.23E2|-1.23E2|-1.23E2|-1.23E2|-1.23E2|  -123.|-1E2|
     |-1.2345679E3|-1.23E3|-1.23E3|-1.23E3|-1.23E3|-1.23E3| -1235.|-1E3|
     |-1.2345679E4|-1.23E4|-1.23E4|-1.23E4|-1.23E4|-1.23E4|-12346.|-1E4|
     |-1.2345679E5|-1.23E5|-1.23E5|-1.23E5|-1.23E5|-1.23E5|-1.23E5|-1E5|

   You can generate a string instead of displaying the number with:

'f>str-rdp' ( rf +nr +nd +np -- c-addr nr  ) gforth-0.6 "f>str-rdp"
   Convert rf into a string at c-addr nr.  The conversion rules and the
meanings of nr +nd np are the same as for 'f.rdp'.  The result in in the
pictured numeric output buffer and will be destroyed by anything
destroying that buffer.

'f>buf-rdp' ( rf c-addr +nr +nd +np --  ) gforth-0.6 "f>buf-rdp"
   Convert rf into a string at c-addr nr.  The conversion rules and the
meanings of nr nd np are the same as for 'f.rdp'.

   There is also a primitive used for implementing higher-level
FP-to-string words:

'represent' ( r c-addr u -- n f1 f2 ) floating "represent"
   Convert the decimal significand (aka mantissa) of r into a string in
buffer c-addr u; n is the exponent, f1 is true if r is negative, and f2
is true if r is valid (a finite number in Gforth).

6.20.4 Miscellaneous output
---------------------------

'cr' ( --  ) core "c-r"
   Output a newline (of the favourite kind of the host OS). Note that
due to the way the Forth command line interpreter inserts newlines, the
preferred way to use 'cr' is at the start of a piece of text; e.g., 'cr
." hello, world"'.

'space' ( --  ) core "space"
   Display one space.

'spaces' ( u --  ) core "spaces"
   Display U spaces.

'out' ( -- addr  ) gforth-1.0 "out"
   'Addr' contains a number that tries to give the position of the
cursor within the current line on the user output device: It resets to 0
on 'cr', increases by the number of characters by 'type' and 'emit', and
decreases on 'backspaces'.  Unfortunately, it does not take into account
tabs, multi-byte characters, or the existence of Unicode characters with
width 0 and 2, so it only works for simple cases.

'.\"' ( compilation 'ccc"' -- ; run-time --  ) gforth-0.6 "dot-backslash-quote"
   Like '."', but translates C-like \-escape-sequences (see 'S\"').

'."' ( compilation 'ccc"' -- ; run-time --  ) core "dot-quote"
   Compilation: Parse a string ccc delimited by a " (double quote).  At
run-time, display the string.  Interpretation semantics for this word
are undefined in standard Forth.  Gforth's interpretation semantics are
to display the string.

'.(' ( compilation&interpretation "ccc<paren>" --  ) core-ext "dot-paren"
   Compilation and interpretation semantics: Parse a string ccc
delimited by a ')' (right parenthesis).  Display the string.  This is
often used to display progress information during compilation; see
examples below.

   If you don't want to worry about wether to use '.( hello)' or '."
hello"', you can write '"hello" type', which gives you what you usually
want (but is less portable to other Forth systems).

As an example, consider the following text, stored in a file 'test.fs':

     .( text-1)
     : my-word
       ." text-2" cr
       .( text-3)
       "text-4" type
     ;

     ." text-5"
     "text-6" type

   When you load this code into Gforth, the following output is
generated:

     include test.fs <RET> text-1text-3text-5text-6 ok

   * Messages 'text-1' and 'text-3' are displayed because '.(' is an
     immediate word; it behaves in the same way whether it is used
     inside or outside a colon definition.
   * Message 'text-5' is displayed because of Gforth's added
     interpretation semantics for '."'.
   * Message 'text-6' is displayed because '"text-6" type' is
     interpreted.
   * Message 'text-2' is not displayed, because the text interpreter
     performs the compilation semantics for '."' within the definition
     of 'my-word'.
   * Message 'text-4' is not displayed, because '"text-4" type' is
     compiled into 'my-word'.

6.20.5 Displaying characters and strings
----------------------------------------

'type' ( c-addr u --  ) core "type"
   If U>0, display U characters from a string starting with the
character stored at C-ADDR.

'xemit' ( xc --  ) xchar "x-emit"
   Prints an xchar on the terminal.

'emit' ( c --  ) core "emit"
   Send the byte c to the current output; for ASCII characters, 'emit'
is equivalent to 'xemit'.

'typewhite' ( addr n --  ) gforth-0.2 "typewhite"
   Like type, but white space is printed instead of the characters.

6.20.6 Terminal output
----------------------

If you are outputting to a terminal, you may want to control the
positioning of the cursor:

'at-xy' ( x y --  ) facility "at-x-y"
   Put the curser at position x y.  The top left-hand corner of the
display is at 0 0.

'at-deltaxy' ( dx dy --  ) gforth-0.7 "at-deltaxy"
   With the current position at x y, put the cursor at x+dx y+dy.

   In order to know where to position the cursor, it is often helpful to
know the size of the screen:

'form' ( -- nlines ncols  ) gforth-0.2 "form"

   And sometimes you want to use:

'page' ( --  ) facility "page"
   Clear the screen

   Note that on non-terminals you should use '12 emit', not 'page', to
get a form feed.

6.20.6.1 Color output
.....................

The following words are used to create (semantic) colorful output;
further output is produced in the color and style given by the word; the
actual color and style depends on the theme (see below).

'default-color' ( --  ) gforth-1.0 "default-color"
   use system-default color

'error-color' ( --  ) gforth-1.0 "error-color"
   error color: red

'error-hl-inv' ( --  ) gforth-1.0 "error-hl-inv"
   color mod for error highlight inverse

'error-hl-ul' ( --  ) gforth-1.0 "error-hl-ul"
   color mod for error highlight underline

'warning-color' ( --  ) gforth-1.0 "warning-color"
   color for warnings: blue/yellow on black terminals

'info-color' ( --  ) gforth-1.0 "info-color"
   color for info: green/cyan on black terminals

'success-color' ( --  ) gforth-1.0 "success-color"
   color for success: green

'input-color' ( --  ) gforth-1.0 "input-color"
   color for user-input: black/white (both bold)

'status-color' ( --  ) gforth-1.0 "status-color"
   color mod for error highlight inverse

6.20.6.2 Color themes
.....................

Depending on wether you prefer bright or dark background the foreground
colors-theme can be changed by:

'light-mode' ( --  ) gforth-1.0 "light-mode"
   color theme for white background

'dark-mode' ( --  ) gforth-1.0 "dark-mode"
   color theme for black background

'uncolored-mode' ( --  ) gforth-1.0 "uncolored-mode"
   This mode does not set colors, but uses the default ones.

'magenta-input' ( --  ) gforth-1.0 "magenta-input"
   make input color easily recognizable (useful in presentations)

6.20.7 Single-key input
-----------------------

If you want to get a single printable character, you can use 'key'; to
check whether a character is available for 'key', you can use 'key?'.

'key' ( -- char  ) core "key"
   Receive (but do not display) one character, CHAR.

'key-ior' ( -- char|ior  ) gforth-1.0 "key-ior"
   Receive (but do not display) one character, CHAR, in case of an error
or interrupt, return the negative IOR instead.

'key?' ( -- flag  ) facility "key-question"
   Determine whether a character is available.  If a character is
available, FLAG is true; the next call to 'key' will yield the
character.  Once 'key?' returns true, subsequent calls to 'key?' before
calling 'key' or 'ekey' will also return true.

'xkey?' ( -- flag  ) xchar "x-key-query"

   If you want to process a mix of printable and non-printable
characters, you can do that with 'ekey' and friends.  'Ekey' produces a
keyboard event that you have to convert into a character with
'ekey>char' or into a key identifier with 'ekey>fkey'.

   Typical code for using EKEY looks like this:

     ekey ekey>xchar if ( xc )
       ... \ do something with the character
     else ekey>fkey if ( key-id )
       case
         k-up                                  of ... endof
         k-f1                                  of ... endof
         k-left k-shift-mask or k-ctrl-mask or of ... endof
         ...
       endcase
     else ( keyboard-event )
       drop \ just ignore an unknown keyboard event type
     then then

'ekey' ( -- u  ) facility-ext "e-key"
   Receive a keyboard event U (encoding implementation-defined).

'ekey>xchar' ( u -- u false | xc true  ) xchar-ext "e-key-to-x-char"
   Convert keyboard event U into xchar 'xc' if possible.

'ekey>char' ( u -- u false | c true  ) facility-ext "e-key-to-char"
   Convert keyboard event U into character 'c' if possible.  Note that
non-ASCII characters produce 'false' from both 'ekey>char' and
'ekey>fkey'.  Instead of 'ekey>char', use 'ekey>xchar' if available.

'ekey>fkey' ( u1 -- u2 f  ) facility-ext "e-key-to-f-key"
   If u1 is a keyboard event in the special key set, convert keyboard
event U1 into key id U2 and return true; otherwise return U1 and false.

'ekey?' ( -- flag  ) facility-ext "e-key-question"
   True if a keyboard event is available.

   The key identifiers for cursor keys are:

'k-left' ( -- u  ) facility-ext "k-left"

'k-right' ( -- u  ) facility-ext "k-right"

'k-up' ( -- u  ) facility-ext "k-up"

'k-down' ( -- u  ) facility-ext "k-down"

'k-home' ( -- u  ) facility-ext "k-home"
   aka Pos1

'k-end' ( -- u  ) facility-ext "k-end"

'k-prior' ( -- u  ) facility-ext "k-prior"
   aka PgUp

'k-next' ( -- u  ) facility-ext "k-next"
   aka PgDn

'k-insert' ( -- u  ) facility-ext "k-insert"

'k-delete' ( -- u  ) facility-ext "k-delete"
   the <DEL> key on my xterm, not backspace

   The key identifiers for function keys (aka keypad keys) are:

'k-f1' ( -- u  ) facility-ext "k-f-1"

'k-f2' ( -- u  ) facility-ext "k-f-2"

'k-f3' ( -- u  ) facility-ext "k-f-3"

'k-f4' ( -- u  ) facility-ext "k-f-4"

'k-f5' ( -- u  ) facility-ext "k-f-5"

'k-f6' ( -- u  ) facility-ext "k-f-6"

'k-f7' ( -- u  ) facility-ext "k-f-7"

'k-f8' ( -- u  ) facility-ext "k-f-8"

'k-f9' ( -- u  ) facility-ext "k-f-9"

'k-f10' ( -- u  ) facility-ext "k-f-10"

'k-f11' ( -- u  ) facility-ext "k-f-11"

'k-f12' ( -- u  ) facility-ext "k-f-12"

   Note that 'k-f11' and 'k-f12' are not as widely available.

   You can combine these key identifiers with masks for various shift
keys:

'k-shift-mask' ( -- u  ) facility-ext "k-shift-mask"

'k-ctrl-mask' ( -- u  ) facility-ext "k-ctrl-mask"

'k-alt-mask' ( -- u  ) facility-ext "k-alt-mask"

   There are a number of keys that have ASCII values, and therefore are
unlikely to be reported as special keys, but the combination of these
keys with shift keys may be reported as a special key:

'k-enter' ( -- u  ) gforth-1.0 "k-enter"

'k-backspace' ( -- u  ) gforth-1.0 "k-backspace"

'k-tab' ( -- u  ) gforth-1.0 "k-tab"

   Moreover, there the following key codes for keys and other events:

'k-winch' ( -- u  ) gforth-1.0 "k-winch"
   A key code that may be generated when the user changes the window
size.

'k-pause' ( -- u  ) gforth-1.0 "k-pause"

'k-mute' ( -- u  ) gforth-1.0 "k-mute"

'k-volup' ( -- u  ) gforth-1.0 "k-volup"

'k-voldown' ( -- u  ) gforth-1.0 "k-voldown"

'k-sel' ( -- u  ) gforth-1.0 "k-sel"
   keycode for Android selections

'k-eof' ( -- u  ) gforth-1.0 "k-eof"

   Note that, even if a Forth system has 'ekey>fkey' and the key
identifier words, the keys are not necessarily available or it may not
necessarily be able to report all the keys and all the possible
combinations with shift masks.  Therefore, write your programs in such a
way that they are still useful even if the keys and key combinations
cannot be pressed or are not recognized.

   Examples: Older keyboards often do not have an F11 and F12 key.  If
you run Gforth in an xterm, the xterm catches a number of combinations
(e.g., <Shift-Up>), and never passes it to Gforth.  Finally, Gforth
currently does not recognize and report combinations with multiple shift
keys (so the <shift-ctrl-left> case in the example above would never be
entered).

   Gforth recognizes various keys available on ANSI terminals (in MS-DOS
you need the ANSI.SYS driver to get that behaviour); it works by
recognizing the escape sequences that ANSI terminals send when such a
key is pressed.  If you have a terminal that sends other escape
sequences, you will not get useful results on Gforth.  Other Forth
systems may work in a different way.

   Gforth also provides a few words for outputting names of function
keys:

'fkey.' ( u --  ) gforth-1.0 "fkey-dot"
   Print a string representation for the function key u.  U must be a
function key (possibly with modifier masks), otherwise there may be an
exception.

'simple-fkey-string' ( u1 -- c-addr u  ) gforth-1.0 "simple-fkey-string"
   c-addr u is the string name of the function key u1.  Only works for
simple function keys without modifier masks.  Any u1 that does not
correspond to a simple function key currently produces an exception.

6.20.8 Line input and conversion
--------------------------------

For ways of storing character strings in memory see *note String
representations::.

   Words for inputting one line from the keyboard:

'accept' ( c-addr +n1 -- +n2  ) core "accept"
   Get a string of up to N1 characters from the user input device and
store it at C-ADDR.  N2 is the length of the received string.  The user
indicates the end by pressing <RET>.  Gforth supports all the editing
functions available on the Forth command line (including history and
word completion) in 'accept'.

'edit-line' ( c-addr n1 n2 -- n3  ) gforth-0.6 "edit-line"
   edit the string with length N2 in the buffer C-ADDR N1, like
'accept'.

   Conversion words:

's>number?' ( addr u -- d f  ) gforth-0.5 "s>number?"
   converts string addr u into d, flag indicates success

's>unumber?' ( c-addr u -- ud flag  ) gforth-0.5 "s>unumber?"
   converts string c-addr u into ud, flag indicates success

'>number' ( ud1 c-addr1 u1 -- ud2 c-addr2 u2  ) core "to-number"
   Attempt to convert the character string C-ADDR1 U1 to an unsigned
number in the current number base.  The double UD1 accumulates the
result of the conversion to form UD2.  Conversion continues,
left-to-right, until the whole string is converted or a character that
is not convertable in the current number base is encountered (including
+ or -).  For each convertable character, UD1 is first multiplied by the
value in 'BASE' and then incremented by the value represented by the
character.  C-ADDR2 is the location of the first unconverted character
(past the end of the string if the whole string was converted).  U2 is
the number of unconverted characters in the string.  Overflow is not
detected.

'>float' ( c-addr u -- f:... flag ) floating "to-float"
   Actual stack effect: ( c_addr u -- r t | f ).  Attempt to convert the
character string c-addr u to internal floating-point representation.  If
the string represents a valid floating-point number, r is placed on the
floating-point stack and flag is true.  Otherwise, flag is false.  A
string of blanks is a special case and represents the floating-point
number 0.

'>float1' ( c-addr u c -- f:... flag ) gforth-1.0 "to-float1"
   Actual stack effect: ( c_addr u c -- r t | f ).  Attempt to convert
the character string c-addr u to internal floating-point representation,
with c being the decimal separator.  If the string represents a valid
floating-point number, r is placed on the floating-point stack and flag
is true.  Otherwise, flag is false.  A string of blanks is a special
case and represents the floating-point number 0.

   Obsolescent input and conversion words:

'convert' ( ud1 c-addr1 -- ud2 c-addr2  ) core-ext-obsolescent "convert"
   Obsolescent: superseded by '>number'.

'expect' ( c-addr +n --  ) core-ext-obsolescent "expect"
   Receive a string of at most +n characters, and store it in memory
starting at c-addr.  The string is displayed.  Input terminates when the
<return> key is pressed or +n characters have been received.  The normal
Gforth line editing capabilites are available.  The length of the string
is stored in 'span'; it does not include the <return> character.
OBSOLESCENT: superceeded by 'accept'.

'span' ( -- c-addr  ) core-ext-obsolescent "span"
   'Variable' -- c-addr is the address of a cell that stores the length
of the last string received by 'expect'.  OBSOLESCENT.

6.20.9 Pipes
------------

In addition to using Gforth in pipes created by other processes (*note
Gforth in pipes::), you can create your own pipe with 'open-pipe', and
read from or write to it.

'open-pipe' ( c-addr u wfam -- wfileid wior ) gforth-0.2 "open-pipe"

'close-pipe' ( wfileid -- wretval wior ) gforth-0.2 "close-pipe"

   If you write to a pipe, Gforth can throw a 'broken-pipe-error'; if
you don't catch this exception, Gforth will catch it and exit, usually
silently (*note Gforth in pipes::).  Since you probably do not want
this, you should wrap a 'catch' or 'try' block around the code from
'open-pipe' to 'close-pipe', so you can deal with the problem yourself,
and then return to regular processing.

'broken-pipe-error' ( -- n  ) gforth-0.6 "broken-pipe-error"
   the error number for a broken pipe

6.20.10 Xchars and Unicode
--------------------------

ASCII is only appropriate for the English language.  Most western
languages however fit somewhat into the Forth frame, since a byte is
sufficient to encode the few special characters in each (though not
always the same encoding can be used; latin-1 is most widely used,
though).  For other languages, different char-sets have to be used,
several of them variable-width.  To deal with this problem, characters
are often represented as Unicode codepoints on the stack, and as UTF-8
byte strings in memory.  An Unicode codepoint often represents one
application-level character, but Unicode also supports decomposed
characters that consist of several code points, e.g., a base letter and
a combining diacritical mark.

   An Unicode codepoint can consume more than one byte in memory, so we
adjust our terminology: A char is a raw byte in memory or a value in the
range 0-255 on the stack.  An xchar (for extended char) stands for one
codepoint; it is represented by one or more bytes in memory and may have
larger values on the stack.  ASCII characters are the same as chars and
as xchars: values in the range 0-127, and a single byte with that value
in memory.

   When using UTF-8 encoding, all other codepoints take more than one
byte/char.  In most cases, you can just treat such characters as strings
in memory and don't need to use the following words, but if you want to
deal with individual codepoints, the following words are useful.  We
currently have no words for dealing with decomposed characters.

   The xchar words add a few data types:

   * XC is an extended char (xchar) on the stack.  It occupies one cell,
     and is a subset of unsigned cell.  On 16 bit systems, only the BMP
     subset of the Unicode character set (i.e., codepoints <65536) can
     be represented on the stack.  If you represent your application
     characters as strings at all times, you can avoid this limitation.

   * XC-ADDR is the address of an xchar in memory.  Alignment
     requirements are the same as C-ADDR.  The memory representation of
     an xchar differs from the stack representation, and depends on the
     encoding used.  An xchar may use a variable number of chars in
     memory.

   * XC-ADDR U is a buffer of xchars in memory, starting at XC-ADDR, U
     chars (i.e., bytes, not xchars) long.

'xc-size' ( xc -- u  ) xchar "x-c-size"
   Computes the memory size of the xchar XC in chars.

'x-size' ( xc-addr u1 -- u2  ) xchar "x-size"
   Computes the memory size of the first xchar stored at XC-ADDR in
chars.

'xc@' ( xc-addr -- xc  ) xchar-ext "xc-fetch"
   Fetchs the xchar XC at XC-ADDR1.

'xc@+' ( xc-addr1 -- xc-addr2 xc  ) xchar "x-c-fetch-plus"
   Fetchs the xchar XC at XC-ADDR1.  XC-ADDR2 points to the first memory
location after XC.

'xc@+?' ( xc-addr1 u1 -- xc-addr2 u2 xc  ) gforth-experimental "x-c-fetch-plus-query"
   Fetchs the first xchar XC of the string XC-ADDR1 U1.  XC-ADDR2 U2 is
the remaining string after XC.

'xc!+?' ( xc xc-addr1 u1 -- xc-addr2 u2 f  ) xchar "x-c-store-plus-query"
   Stores the xchar XC into the buffer starting at address XC-ADDR1, U1
chars large.  XC-ADDR2 points to the first memory location after XC, U2
is the remaining size of the buffer.  If the xchar XC did fit into the
buffer, F is true, otherwise F is false, and XC-ADDR2 U2 equal XC-ADDR1
U1.  XC!+?  is safe for buffer overflows, and therefore preferred over
XC!+.

'xc!+' ( xc xc-addr1 -- xc-addr2  ) xchar "x-c-store"
   Stores the xchar XC at XC-ADDR1.  XC-ADDR2 is the next unused address
in the buffer.  Note that this writes up to 4 bytes, so you need at
least 3 bytes of padding after the end of the buffer to avoid
overwriting useful data if you only check the address against the end of
the buffer.

'xchar+' ( xc-addr1 -- xc-addr2  ) xchar "x-char-plus"
   Adds the size of the xchar stored at XC-ADDR1 to this address, giving
XC-ADDR2.

'xchar-' ( xc-addr1 -- xc-addr2  ) xchar-ext "x-char-minus"
   Goes backward from XC_ADDR1 until it finds an xchar so that the size
of this xchar added to XC_ADDR2 gives XC_ADDR1.

'+x/string' ( xc-addr1 u1 -- xc-addr2 u2  ) xchar-ext "plus-x-slash-string"
   Step forward by one xchar in the buffer defined by address XC-ADDR1,
size U1 chars.  XC-ADDR2 is the address and u2 the size in chars of the
remaining buffer after stepping over the first xchar in the buffer.

'x\string-' ( xc-addr u1 -- xc-addr u2  ) xchar-ext "x-backslash-string-minus"
   Step backward by one xchar in the buffer defined by address XC-ADDR
and size U1 in chars, starting at the end of the buffer.  XC-ADDR is the
address and U2 the size in chars of the remaining buffer after stepping
backward over the last xchar in the buffer.

'-trailing-garbage' ( xc-addr u1 -- xc-addr u2  ) xchar-ext "minus-trailing-garbage"
   Examine the last XCHAR in the buffer XC-ADDR U1---if the encoding is
correct and it repesents a full char, U2 equals U1, otherwise, U2
represents the string without the last (garbled) xchar.

'x-width' ( xc-addr u -- n  ) xchar-ext "x-width"
   N is the number of monospace ASCII chars that take the same space to
display as the the xchar string starting at XC-ADDR, using U chars;
assuming a monospaced display font, i.e.  char width is always an
integer multiple of the width of an ASCII char.

'xkey' ( -- xc  ) xchar "x-key"
   Reads an xchar from the terminal.  This will discard all input events
up to the completion of the xchar.

'xc-width' ( xc -- n  ) xchar-ext "x-c-width"
   XC has a width of N times the width of a normal fixed-width glyph.

'xhold' ( xc --  ) xchar-ext "x-hold"
   Used between '<<#' and '#>'.  Prepend XC to the pictured numeric
output string.  Alternatively, use 'holds'.

'xc,' ( xchar --  ) xchar "x-c-comma"

6.20.11 Internationalization and Localization
---------------------------------------------

Programs for end users require to address those in their native
language.  There is a decades old proposal for such a facility that has
been split from other proposals for international character sets like
Xchars (*note Xchars and Unicode::) and Substitute (*note Substitute::).
Messages displayed on the screen need to be translated from the native
language of the developers to the local languages of the user.

   Strings subject to translation are declared with 'L" 'STRING'"'.
This returns a locale string identifier (LSID). LSIDs are opaque types,
taking a cell on the stack.  LSIDs can be translated into a locale;
locales are languages and country-specific variants of that language.

'L"' ( "lsid<">" -- lsid  ) gforth-experimental "l-quote"
   Parse a string and define a new lsid, if the string is uniquely new.
Identical strings result in identical lsids, which allows to refer to
the same lsid from multiple locations using the same string.

'LU"' ( "lsid<">" -- lsid  ) gforth-experimental "l-unique-quote"
   Parse a string and always define a new lsid, even if the string is
not unique.

'native@' ( lsid -- addr u  ) gforth-experimental "native-fetch"
   fetch native string from an LSID

'locale@' ( lsid -- addr u  ) gforth-experimental "locale-fetch"
   fetch the localized string in the current language and country

'locale!' ( addr u lsid --  ) gforth-experimental "locale-store"
   Store localized string ADDR U for the current locale and country in
LSID.

'Language' ( "name" --  ) gforth-experimental "Language"
   define a locale.  Executing that locale makes it the current locale.

'Country' ( <lang> "name" --  ) gforth-experimental "Country"
   define a variant (typical: country) for the current locale.
Executing that locale makes it the current locale.  You can create
variants of variants (a country may have variants within, e.g.  think of
how many words for rolls/buns there are in many languages).

'locale-file' ( fid --  ) gforth-experimental "locale-file"
   read lines from FID into the current locale.

'included-locale' ( addr u --  ) gforth-experimental "included-locale"
   read lines from the file ADDR U into the current locale.

'include-locale' ( "name" --  ) gforth-experimental "include-locale"
   read lines from the file "NAME" into the current locale.

'locale-csv' ( "name" --  ) gforth-experimental "locale-csv"
   import comma-separated value table into locales.  first line contains
locale names, "program" and "default" are special entries; generic
languages must preceed translations for specific countries.  Entries
under "program" (must be leftmost) are used to search for the lsid; if
empty, the line number-1 is the lsid index.

'.locale-csv' ( --  ) gforth-experimental "dot-locale-csv"
   write the locale database in CSV format to the terminal output.

'locale-csv-out' ( "name" --  ) gforth-experimental "locale-csv"
   Create file "NAME" and write the locale database out to the file
"NAME" in CSV format.

6.20.12 Substitute
------------------

This is a simple text macro replacement facility.  Texts in the form
'"text %macro% text"' are processed, and the macro variables enclosed in
''%'' are replaced with their associated strings.  Two consecutive '%'
are replaced by one '%'.  Macros are defined in a specific wordlist, and
return a string upon execution; the standard defines only one way to
declare macros, 'replaces', which creates a macro that just returns a
string.

'macros-wordlist' ( -- wid  ) gforth-experimental "macros-wordlist"
   wordlist for string replacement macros

'replaces' ( addr1 len1 addr2 len2 --  ) string-ext "replaces"
   create a macro with name ADDR2 LEN2 and content ADDR1 LEN1.  If the
macro already exists, just change the content.

'.substitute' ( addr1 len1 -- n / ior  ) gforth-experimental "dot-substitute"
   substitute all macros in text ADDR1 LEN1 and print the result.  N is
the number of substitutions or, if negative, a throwable IOR.

'$substitute' ( addr1 len1 -- addr2 len2 n/ior  ) gforth-experimental "string-substitute"
   substitute all macros in text ADDR1 LEN1.  N is the number of
substitutions, if negative, it's a throwable IOR, ADDR2 LEN2 the result.

'substitute' ( addr1 len1 addr2 len2 -- addr2 len3 n/ior  ) string-ext "substitute"
   substitute all macros in text ADDR1 LEN1, and copy the result to
ADDR2 LEN2.  N is the number of substitutions or, if negative, a
throwable IOR, ADDR2 LEN3 the result.

'unescape' ( addr1 u1 dest -- dest u2  ) string-ext "unescape"
   double all delimiters in ADDR1 U1, so that substitute will result in
the original text.  Note that the buffer DEST does not have a size, as
in worst case, it will need just twice as many characters as U1.  DEST
U2 is the resulting string.

'$unescape' ( addr1 u1 -- addr2 u2  ) gforth-experimental "string-unescape"
   same as 'unescape', but creates a temporary destination string with
'$tmp'.

6.20.13 CSV Reader
------------------

Comma-separated values (CSV) are a popular text format to interchange
data.  Gforth provides an reader in 'csv.fs'.

'read-csv' ( addr u xt --  ) gforth-experimental "read-csv"
   read CVS file ADDR U and execute XT for every item found.  XT takes
'( addr u col line -- )', i.e.  the string, the current column (starting
with 0), and the current line (starting with 1).

6.21 OS command line arguments
==============================

The usual way to pass arguments to Gforth programs on the command line
is via the '-e' option, e.g.

     gforth -e "123 456" foo.fs -e bye

   However, you may want to interpret the command-line arguments
directly.  In that case, you can access the (image-specific)
command-line arguments through 'next-arg':

'next-arg' ( -- addr u  ) gforth-0.7 "next-arg"
   get the next argument from the OS command line, consuming it; if
there is no argument left, return '0 0'.

   Here's an example program 'echo.fs' for 'next-arg':

     : echo ( -- )
         begin
     	next-arg 2dup 0 0 d<> while
     	    type space
         repeat
         2drop ;

     echo cr bye

   This can be invoked with

     gforth echo.fs hello world

   and it will print

     hello world

   The next lower level of dealing with the OS command line are the
following words:

'arg' ( u -- addr count  ) gforth-0.2 "arg"
   Return the string for the uth command-line argument; returns '0 0' if
the access is beyond the last argument.  '0 arg' is the program name
with which you started Gforth.  The next unprocessed argument is always
'1 arg', the one after that is '2 arg' etc.  All arguments already
processed by the system are deleted.  After you have processed an
argument, you can delete it with 'shift-args'.

'shift-args' ( --  ) gforth-0.7 "shift-args"
   '1 arg' is deleted, shifting all following OS command line parameters
to the left by 1, and reducing 'argc @'.  This word can change 'argv @'.

   Finally, at the lowest level Gforth provides the following words:

'argc' ( -- addr  ) gforth-0.2 "argc"
   'Variable' -- the number of command-line arguments (including the
command name).  Changed by 'next-arg' and 'shift-args'.

'argv' ( -- addr  ) gforth-0.2 "argv"
   'Variable' -- a pointer to a vector of pointers to the command-line
arguments (including the command-name).  Each argument is represented as
a C-style zero-terminated string.  Changed by 'next-arg' and
'shift-args'.

6.22 Locals
===========

Local variables can make Forth programming more enjoyable and Forth
programs easier to read.  Unfortunately, the locals of Standard Forth
are laden with restrictions.  Therefore, we provide not only the
Standard Forth locals wordset, but also our own, more powerful locals
wordset (we implemented the Standard Forth locals wordset through our
locals wordset).

   The ideas in this section have also been published in M. Anton Ertl,
'Automatic Scoping of Local Variables
(https://www.complang.tuwien.ac.at/papers/ertl94l.ps.gz)', EuroForth
'94.

6.22.1 Gforth locals
--------------------

Locals can be defined with

     {: local1 local2 ... -- comment :}
   or
     {: local1 local2 ... :}
   or
     {: local1 local2 ... | ulocal0 ulocal1 -- comment :}

   E.g.,
     : max {: n1 n2 -- n3 :}
      n1 n2 > if
        n1
      else
        n2
      endif ;

   The similarity of locals definitions with stack comments is intended.
A locals definition often replaces the stack comment of a word.  The
order of the locals corresponds to the order in a stack comment and
everything after the '--' is really a comment.

   This similarity has one disadvantage: It is too easy to confuse
locals declarations with stack comments, causing bugs and making them
hard to find.  However, this problem can be avoided by appropriate
coding conventions: Do not use both notations in the same program.  If
you do, they should be distinguished using additional means, e.g.  by
position.

   The name of the local may be preceded by a type specifier, e.g., 'F:'
for a floating point value:

     : CX* {: F: Ar F: Ai F: Br F: Bi -- Cr Ci :}
     \ complex multiplication
      Ar Br f* Ai Bi f* f-
      Ar Bi f* Ai Br f* f+ ;

   Gforth currently supports cells ('W:', 'WA:', 'W^'), doubles ('D:',
'DA:', 'D^'), floats ('F:', 'FA:', 'F^'), characters ('C:', 'CA:',
'C^'), and xts ('xt:', 'xta:') in several flavours:

"value-flavoured"
     (*note Values::) A value-flavoured local (defined with 'W:', 'D:'
     etc.)  produces its value and can be changed with 'TO'.

"varue-flavoured"
     (*note Varues::) A varue-flavoured local l (defined with 'WA:'
     etc.)  behaves exactly like a value-flavoured local, except that
     you can use 'addr l' to get its address (which becomes invalid when
     the variable's scope is left).  Currently there is no performance
     difference, but in the long run value-flavoured locals will be
     significantly faster, because they can reside in registers.

"variable-flavoured"
     (*note Variables::) A variable-flavoured local (defined with 'W^'
     etc.)  produces its address (which becomes invalid when the
     variable's scope is left).  E.g., the standard word 'emit' can be
     defined in terms of 'type' like this:

          : emit {: C^ char* -- :}
              char* 1 type ;

"defer-flavoured"
     (*note Deferred Words::) A defer-flavoured local (defined with
     'XT:' or 'XTA:') 'execute's the xt; you can use 'action-of' (*note
     Deferred Words::) to get the xt out of a defer-flavoured local.  If
     the local is defined with 'xta:', you can use 'addr' to get the
     address (valid until the end of the scope of the local) where the
     xt is stored.  E.g., the standard word 'execute' can be defined
     with a defer-flavoured local like this:

          : execute {: xt: x -- :}
            x ;

   A local without type specifier is a 'W:' local.  You can allow or
disallow the use of 'addr' with:

'default-wa:' ( --  ) gforth-experimental "default-wa:"
   Allow 'addr' on locals defined without a type specifyer.  On other
words, define locals without a type specifyer using 'wa:'.

'default-w:' ( --  ) gforth-experimental "default-w:"
   Forbid 'addr' on locals defined without a type specifyer.  On other
words, define locals without a type specifyer using 'w:'.

   All flavours of locals are initialized with values from the data or
(for FP locals) FP stack, with the exception being locals defined behind
'|': Gforth initializes them to 0; some Forth systems leave them
uninitialized.

   Gforth supports the square bracket notation for local buffers and
data structures.  These locals are similar to variable-flavored locals,
the size is specified as a constant expression.  A declaration looks
'name[ size ]'.  The Forth expression 'size' is evaluated during
declaration, it must have the stack effect '( -- +n )', giving the size
in bytes.  The square bracket '[' is part of the defined name.

   Local data structures are initialized by copying size bytes from an
address passed on the stack; uninitialized local data structures (after
'|' in the declaration) are not erased, they just contain whatever data
there was on the locals stack before.

   Example:

     begin-structure test-struct
       field: a1
       field: a2
     end-structure

     : test-local {: foo[ test-struct ] :}
         foo[ a1 !  foo[ a2 !
         foo[ test-struct dump ;

   Gforth allows defining locals everywhere in a colon definition.  This
poses the following questions:

6.22.1.1 Locals definitions words
.................................

This section documents the words used for defining locals.  Note that
the run-times for the words (like 'W:') that define a local are
performed from the rightmost defined local to the leftmost defined
local, such that the rightmost local gets the top of stack.

'{:' ( -- hmaddr u latest latestnt wid 0  ) local-ext "open-brace-colon"
   Start locals definitions.

'--' ( hmaddr u latest latestnt wid 0 ... --  ) gforth-0.2 "dash-dash"
   During locals definitions everything from '--' to ':}' is ignored.
This is typically used when you want to make a locals definition serve
double duty as a stack effect description.

'|' ( --  ) gforth-1.0 "bar"
   Locals defined behind '|' are not initialized from the stack; so the
run-time of words like 'W:' changes to '( -- )'.

':}' ( hmaddr u latest latestnt wid 0 xt1 ... xtn --  ) gforth-1.0 "colon-close-brace"
   Ends locals definitions.

'{' ( -- hmaddr u latest latestnt wid 0  ) gforth-0.2 "open-brace"
   Start locals definitions.  The Forth-2012 standard name for this word
is '{:'.

'}' ( hmaddr u latest latestnt wid 0 xt1 ... xtn --  ) gforth-0.2 "close-brace"
   Ends locals definitions.  The Forth-2012 standard name for this word
is ':}'.

'W:' ( compilation "name" -- a-addr xt; run-time x --  ) gforth-0.2 "w-colon"
   Define value-flavoured cell local name '( -- x1 )'

'WA:' ( compilation "name" -- a-addr xt; run-time x --  ) gforth-1.0 "w-a-colon"
   Define varue-flavoured cell local name '( -- x1 )'

'W^' ( compilation "name" -- a-addr xt; run-time x --  ) gforth-0.2 "w-caret"
   Define variable-flavoured cell local name '( -- a-addr )'

'D:' ( compilation "name" -- a-addr xt; run-time x1 x2 --  ) gforth-0.2 "d-colon"
   Define value-flavoured double local name '( -- x3 x4 )'

'DA:' ( compilation "name" -- a-addr xt; run-time x1 x2 --  ) gforth-1.0 "w-a-colon"
   Define varue-flavoured double local name '( -- x3 x4 )'

'D^' ( compilation "name" -- a-addr xt; run-time x1 x2 --  ) gforth-0.2 "d-caret"
   Define variable-flavoured double local name '( -- a-addr )'

'C:' ( compilation "name" -- a-addr xt; run-time c --  ) gforth-0.2 "c-colon"
   Define value-flavoured char local name '( -- c1 )'

'CA:' ( compilation "name" -- a-addr xt; run-time c --  ) gforth-1.0 "c-a-colon"
   Define varue-flavoured char local name '( -- c1 )'

'C^' ( compilation "name" -- a-addr xt; run-time c --  ) gforth-0.2 "c-caret"
   Define variable-flavoured char local name '( -- c-addr )'

'F:' ( compilation "name" -- a-addr xt; run-time r --  ) gforth-0.2 "f-colon"
   Define value-flavoured float local name '( -- r1 )'

'FA:' ( compilation "name" -- a-addr xt; run-time f --  ) gforth-1.0 "f-a-colon"
   Define varue-flavoured float local name '( -- r1 )'

'F^' ( compilation "name" -- a-addr xt; run-time r --  ) gforth-0.2 "f-caret"
   Define variable-flavoured float local name '( -- f-addr )'

'XT:' ( compilation "name" -- a-addr xt; run-time xt1 --  ) gforth-1.0 "x-t-colon"
   Define defer-flavoured cell local name '( ... -- ... )'

'XTA:' ( compilation "name" -- a-addr xt; run-time ... -- ...  ) gforth-1.0 "x-t-a-colon"
   Define a defer-flavoured local name on which 'addr' can be used.

   Note that '|', '--', ':}' and '}' are not normally in the search
order (they are in the vocabulary 'locals-types'), and they are not
necessarily words in all Forth systems; therefore they are documented as
Gforth words.

6.22.1.2 Where are locals visible by name?
..........................................

Basically, the answer is that locals are visible where you would expect
it in block-structured languages, and sometimes a little longer.  If you
want to restrict the scope of a local, enclose its definition in
'SCOPE'...'ENDSCOPE'.

'scope' ( compilation  -- scope ; run-time  --  ) gforth-0.2 "scope"

'endscope' ( compilation scope -- ; run-time  --  ) gforth-0.2 "endscope"

   These words behave like control structure words, so you can use them
with 'CS-PICK' and 'CS-ROLL' to restrict the scope in arbitrary ways.

   If you want a more exact answer to the visibility question, here's
the basic principle: A local is visible in all places that can only be
reached through the definition of the local(1).  In other words, it is
not visible in places that can be reached without going through the
definition of the local.  E.g., locals defined in 'IF'...'ENDIF' are
visible until the 'ENDIF', locals defined in 'BEGIN'...'UNTIL' are
visible after the 'UNTIL' (until, e.g., a subsequent 'ENDSCOPE').

   The reasoning behind this solution is: We want to have the locals
visible as long as it is meaningful.  The user can always make the
visibility shorter by using explicit scoping.  In a place that can only
be reached through the definition of a local, the meaning of a local
name is clear.  In other places it is not: How is the local initialized
at the control flow path that does not contain the definition?  Which
local is meant, if the same name is defined twice in two independent
control flow paths?

   This should be enough detail for nearly all users, so you can skip
the rest of this section.  If you really must know all the gory details
and options, read on.

   In order to implement this rule, the compiler has to know which
places are unreachable.  It knows this automatically after 'AHEAD',
'AGAIN', 'EXIT' and 'LEAVE'; in other cases (e.g., after most 'THROW's),
you can use the word 'UNREACHABLE' to tell the compiler that the control
flow never reaches that place.  If 'UNREACHABLE' is not used where it
could, the only consequence is that the visibility of some locals is
more limited than the rule above says.  If 'UNREACHABLE' is used where
it should not (i.e., if you lie to the compiler), buggy code will be
produced.

'UNREACHABLE' ( --  ) gforth-0.2 "UNREACHABLE"

   Another problem with this rule is that at 'BEGIN', the compiler does
not know which locals will be visible on the incoming back-edge.  All
problems discussed in the following are due to this ignorance of the
compiler (we discuss the problems using 'BEGIN' loops as examples; the
discussion also applies to '?DO' and other loops).  Perhaps the most
insidious example is:
     AHEAD
     BEGIN
       x
     [ 1 CS-ROLL ] THEN
       {: x :}
       ...
     UNTIL

   This should be legal according to the visibility rule.  The use of
'x' can only be reached through the definition; but that appears
textually below the use.

   From this example it is clear that the visibility rules cannot be
fully implemented without major headaches.  Our implementation treats
common cases as advertised and the exceptions are treated in a safe way:
The compiler makes a reasonable guess about the locals visible after a
'BEGIN'; if it is too pessimistic, the user will get a spurious error
about the local not being defined; if the compiler is too optimistic, it
will notice this later and issue a warning.  In the case above the
compiler would complain about 'x' being undefined at its use.  You can
see from the obscure examples in this section that it takes quite
unusual control structures to get the compiler into trouble, and even
then it will often do fine.

   If the 'BEGIN' is reachable from above, the most optimistic guess is
that all locals visible before the 'BEGIN' will also be visible after
the 'BEGIN'.  This guess is valid for all loops that are entered only
through the 'BEGIN', in particular, for normal
'BEGIN'...'WHILE'...'REPEAT' and 'BEGIN'...'UNTIL' loops and it is
implemented in our compiler.  When the branch to the 'BEGIN' is finally
generated by 'AGAIN' or 'UNTIL', the compiler checks the guess and warns
the user if it was too optimistic:
     IF
       {: x :}
     BEGIN
       \ x ?
     [ 1 cs-roll ] THEN
       ...
     UNTIL

   Here, 'x' lives only until the 'BEGIN', but the compiler
optimistically assumes that it lives until the 'THEN'.  It notices this
difference when it compiles the 'UNTIL' and issues a warning.  The user
can avoid the warning, and make sure that 'x' is not used in the wrong
area by using explicit scoping:
     IF
       SCOPE
       {: x :}
       ENDSCOPE
     BEGIN
     [ 1 cs-roll ] THEN
       ...
     UNTIL

   Since the guess is optimistic, there will be no spurious error
messages about undefined locals.

   If the 'BEGIN' is not reachable from above (e.g., after 'AHEAD' or
'EXIT'), the compiler cannot even make an optimistic guess, as the
locals visible after the 'BEGIN' may be defined later.

   It pessimistically assumes that all locals are visible that were
visible at the latest place outside any control structure (i.e., where
nothing is on the control-flow stack).  This means that in:

     : foo
       IF {: z :} THEN
       {: x :}
       AHEAD
         BEGIN
           ( * )
         [ 1 CS-ROLL ] THEN
         {: y :}
         ...
       UNTIL ;

   At the place marked with '( * )', 'x' is visible, but 'y' is not
(although, according to the reachability rule it should); 'z' is not and
should not be visible there.

   However, you can use 'ASSUME-LIVE' to make the compiler assume that
the same locals are visible at the BEGIN as at the point where the top
control-flow stack item was created.

'ASSUME-LIVE' ( orig -- orig  ) gforth-0.2 "ASSUME-LIVE"

E.g.,
     IF
       {: x :}
       AHEAD
         ASSUME-LIVE
         BEGIN
           x
         [ 1 CS-ROLL ] THEN
         ...
       UNTIL
     THEN

   Here 'x' would not be visible at the use of 'x', because its
definition is inside a control structure, but by using ASSUME-LIVE the
programmer tells the compiler that the locals visible at the 'AHEAD'
should be visible at the 'BEGIN'.

   Other cases where the locals are defined before the 'BEGIN' can be
handled by inserting an appropriate 'CS-ROLL' before the 'ASSUME-LIVE'
(and changing the control-flow stack manipulation behind the
'ASSUME-LIVE').

   Cases where locals are defined after the 'BEGIN' (but should be
visible immediately after the 'BEGIN') can only be handled by
rearranging the loop.  E.g., the "most insidious" example above can be
arranged into:
     BEGIN
       {: x :}
       ... 0=
     WHILE
       x
     REPEAT

   ---------- Footnotes ----------

   (1) In compiler construction terminology, all places dominated by the
definition of the local.

6.22.1.3 How long do locals live?
.................................

The right answer for the lifetime question would be: A local lives at
least as long as it can be accessed.  For a value-flavoured local this
means: until the end of its visibility.  However, a variable-flavoured
local could be accessed through its address far beyond its visibility
scope.  Ultimately, this would mean that such locals would have to be
garbage collected.  Since this entails un-Forth-like implementation
complexities, I adopted the same cowardly solution as some other
languages (e.g., C): The local lives only as long as it is visible;
afterwards its address is invalid (and programs that access it
afterwards are erroneous).

6.22.1.4 Locals programming style
.................................

The freedom to define locals anywhere has the potential to change
programming styles dramatically.  In particular, the need to use the
return stack for intermediate storage vanishes.  Moreover, all stack
manipulations (except 'PICK's and 'ROLL's with run-time determined
arguments) can be eliminated: If the stack items are in the wrong order,
just write a locals definition for all of them; then write the items in
the order you want.

   This seems a little far-fetched and eliminating stack manipulations
is unlikely to become a conscious programming objective.  Still, the
number of stack manipulations will be reduced dramatically if local
variables are used liberally (e.g., compare 'max' (*note Gforth
locals::) with a traditional implementation of 'max').

   This shows one potential benefit of locals: making Forth programs
more readable.  Of course, this benefit will only be realized if the
programmers continue to honour the principle of factoring instead of
using the added latitude to make the words longer.

   Using 'TO' can and should be avoided.  Without 'TO', every
value-flavoured local has only a single assignment and many advantages
of functional languages apply to Forth.  I.e., programs are easier to
analyse, to optimize and to read: It is clear from the definition what
the local stands for, it does not turn into something different later.

   E.g., a definition using 'TO' might look like this:
     : strcmp {: addr1 u1 addr2 u2 -- n :}
      u1 u2 min 0
      ?do
        addr1 c@ addr2 c@ -
        ?dup-if
          unloop exit
        then
        addr1 char+ TO addr1
        addr2 char+ TO addr2
      loop
      u1 u2 - ;
   Here, 'TO' is used to update 'addr1' and 'addr2' at every loop
iteration.  'strcmp' is a typical example of the readability problems of
using 'TO'.  When you start reading 'strcmp', you think that 'addr1'
refers to the start of the string.  Only near the end of the loop you
realize that it is something else.

   This can be avoided by defining two locals at the start of the loop
that are initialized with the right value for the current iteration.
     : strcmp {: addr1 u1 addr2 u2 -- n :}
      addr1 addr2
      u1 u2 min 0
      ?do {: s1 s2 :}
        s1 c@ s2 c@ -
        ?dup-if
          unloop exit
        then
        s1 char+ s2 char+
      loop
      2drop
      u1 u2 - ;
   Here it is clear from the start that 's1' has a different value in
every loop iteration.

6.22.1.5 Locals implementation
..............................

Gforth uses an extra locals stack.  The most compelling reason for this
is that the return stack is not float-aligned; using an extra stack also
eliminates the problems and restrictions of using the return stack as
locals stack.  Like the other stacks, the locals stack grows toward
lower addresses.  A few primitives allow an efficient implementation;
you should not use them directly, but they appear in the output of
'see', so they are documented here:

'@localn' ( noffset -- w ) gforth-1.0 "fetch-local-n"

'f@localn' ( noffset -- r ) gforth-1.0 "f-fetch-local-n"

'lp@' ( -- c-addr ) gforth-0.2 "lp-fetch"
   C_addr is the current value of the locals stack pointer.

   doc-lp+!#
'lp!' ( c-addr -- ) gforth-internal "lp-store"

'>l' ( w -- ) gforth-0.2 "to-l"

'f>l' ( r -- ) gforth-0.2 "f-to-l"

   In addition to these primitives, some specializations of these
primitives for commonly occurring inline arguments are provided for
efficiency reasons, e.g., '@local0' as specialization of '0 @localn'.
The following compiling words compile the right specialized version, or
the general version, as appropriate:

'compile-lp+!' ( n --  ) gforth-0.2 "compile-l-p-plus-store"

   Combinations of conditional branches and 'lp+!#' like '?branch-lp+!#'
(the locals pointer is only changed if the branch is taken) are provided
for efficiency and correctness in loops.

   A special area in the dictionary space is reserved for keeping the
local variable names.  '{:' switches the dictionary pointer to this area
and ':}' switches it back and generates the locals initializing code.
'W:' etc. are normal defining words.  This special area is cleared at
the start of every colon definition.

   A special feature of Gforth's dictionary is used to implement the
definition of locals without type specifiers: every word list (aka
vocabulary) has its own methods for searching etc.  (*note Word
Lists::).  For the present purpose we defined a word list with a special
search method: When it is searched for a word, it actually creates that
word using 'W:'.  '{:' changes the search order to first search the word
list containing ':}', 'W:' etc., and then the word list for defining
locals without type specifiers.

   The lifetime rules support a stack discipline within a colon
definition: The lifetime of a local is either nested with other locals
lifetimes or it does not overlap them.

   At 'BEGIN', 'IF', and 'AHEAD' no code for locals stack pointer
manipulation is generated.  Between control structure words locals
definitions can push locals onto the locals stack.  'AGAIN' is the
simplest of the other three control flow words.  It has to restore the
locals stack depth of the corresponding 'BEGIN' before branching.  The
code looks like this:
'lp+!#' current-locals-size - dest-locals-size
'branch' <begin>

   'UNTIL' is a little more complicated: If it branches back, it must
adjust the stack just like 'AGAIN'.  But if it falls through, the locals
stack must not be changed.  The compiler generates the following code:
'?branch-lp+!#' <begin> current-locals-size - dest-locals-size
   The locals stack pointer is only adjusted if the branch is taken.

   'THEN' can produce somewhat inefficient code:
'lp+!#' current-locals-size - orig-locals-size
<orig target>:
'lp+!#' orig-locals-size - new-locals-size
   The second 'lp+!#' adjusts the locals stack pointer from the level at
the orig point to the level after the 'THEN'.  The first 'lp+!#' adjusts
the locals stack pointer from the current level to the level at the orig
point, so the complete effect is an adjustment from the current level to
the right level after the 'THEN'.

   In a conventional Forth implementation a dest control-flow stack
entry is just the target address and an orig entry is just the address
to be patched.  Our locals implementation adds a word list to every orig
or dest item.  It is the list of locals visible (or assumed visible) at
the point described by the entry.  Our implementation also adds a tag to
identify the kind of entry, in particular to differentiate between live
and dead (reachable and unreachable) orig entries.

   A few unusual operations have to be performed on locals word lists:

'common-list' ( list1 list2 -- list3  ) gforth-internal "common-list"

'sub-list?' ( list1 list2 -- f  ) gforth-internal "sub-list?"

'list-size' ( list -- u  ) gforth-internal "list-size"

   Several features of our locals word list implementation make these
operations easy to implement: The locals word lists are organised as
linked lists; the tails of these lists are shared, if the lists contain
some of the same locals; and the address of a name is greater than the
address of the names behind it in the list.

   Another important implementation detail is the variable 'dead-code'.
It is used by 'BEGIN' and 'THEN' to determine if they can be reached
directly or only through the branch that they resolve.  'dead-code' is
set by 'UNREACHABLE', 'AHEAD', 'EXIT' etc., and cleared at the start of
a colon definition, by 'BEGIN' and usually by 'THEN'.

   Counted loops are similar to other loops in most respects, but
'LEAVE' requires special attention: It performs basically the same
service as 'AHEAD', but it does not create a control-flow stack entry.
Therefore the information has to be stored elsewhere; traditionally, the
information was stored in the target fields of the branches created by
the 'LEAVE's, by organizing these fields into a linked list.
Unfortunately, this clever trick does not provide enough space for
storing our extended control flow information.  Therefore, we introduce
another stack, the leave stack.  It contains the control-flow stack
entries for all unresolved 'LEAVE's.

   Local names are kept until the end of the colon definition, even if
they are no longer visible in any control-flow path.  In a few cases
this may lead to increased space needs for the locals name area, but
usually less than reclaiming this space would cost in code size.

6.22.1.6 Closures
.................

Gforth also provides basic closures.  A closure is a combination of a
quotation (*note Quotations::) and locals.  Gforth's closures have
locals which are filled with values at the closure's run-time, producing
a trampoline xt.  When executing that trampoline xt, the closure's code
is executed, with access to the closure's locals on the locals stack.
Modifications of the closure's locals aren't persistent, i.e.  when the
closure 'EXIT's, the modified values are lost.

'[{:' ( -- hmaddr u latest latestnt wid 0  ) gforth-experimental "start-closure"
   starts a closure.  Closures first declare the locals frame they are
going to use, and then the code that is executed with those locals.
Closures end like quotations with a ';]'.  The locals declaration ends
depending where the closure's locals are created.  At run-time, the
closure is created as trampolin xt, and fills the values of its local
frame from the stack.  At execution time of the xt, the local frame is
copied to the locals stack, and used inside the closure's code.  After
return, those values are removed from the locals stack, and not updated
in the closure itself.

':}l' ( hmaddr u latest latestnt wid 0 a-addr1 u1 ... --  ) gforth-1.0 "close-brace-locals"
   end a closure's locals declaration.  The closure will be allocated on
the local's stack.

':}d' ( hmaddr u latest latestnt wid 0 a-addr1 u1 ... --  ) gforth-1.0 "colon-close-brace-d"
   end a closure's locals declaration.  The closure will be allocated in
the dictionary.

':}h' ( hmaddr u latest latestnt wid 0 a-addr1 u1 ... --  ) gforth-1.0 "colon-close-brace-h"
   end a closure's locals declaration.  The closure will be allocated on
the heap.

':}h1' ( hmaddr u latest latestnt wid 0 a-addr1 u1 ... --  ) gforth-1.0 "colon-close-brace-h"
   end a closure's locals declaration.  The closure will be allocated on
the heap.

':}xt' ( hmaddr u latest latestnt wid 0 a-addr1 u1 ... --  ) gforth-1.0 "colon-close-brace-x-t"
   end a closure's locals declaration.  The closure will be allocated by
the xt on the stack, so the closure's run-time stack effect is '(
xt-alloc -- xt-closure )'.

'>addr' ( xt -- addr  ) gforth-experimental "to-addr"
   convert the xt of a closure on the heap to the ADDR with can be
passed to 'free' to get rid of the closure

'free-closure' ( xt --  ) gforth-internal "free-closure"
   free a heap-allocated closure

     : foo [{: a f: b d: c xt: d :}d a . b f. c d. d ;] ;
     5 3.3e #1234. ' cr foo execute

   'foo' creates a closure in the dictionary with a single cell, a
floating point, a double, and an xt, and prints the first three values
before executing the xt on invocation.

   This allows to implement Donald Knuth's "Man or boy test" proposed in
1964 to test Algol compilers.

     : A {: w^ k x1 x2 x3 xt: x4 xt: x5 | w^ B :} recursive
         k  0<= IF  x4 x5 f+  ELSE
             B k x1 x2 x3 action-of x4 [{: B k x1 x2 x3 x4 :}L
                 -1 k +!
                 k  B  x1 x2 x3 x4 A ;] dup B !
             execute  THEN ;
     : man-or-boy? ( n -- ) [: 1e ;] [: -1e ;] 2dup swap [: 0e ;] A f. ;

   Sometimes, closures need a permanent storage to be modified; it is
even possible that more than one closure shares that permanent storage.
In the example above, local variables of the outer procedure are used
for this, but in some cases, the closure lives longer than the outer
procedure; especially closures allocated in the dictionary or on the
heap are designed to outlive their parent procedure.

   For those, we have home locations, which are allocated like closures,
but their code is directly executed at creation and should provide us
with the addresses of the home locations.

     : bar ( a b c -- aaddr baddr caddr hl-addr )
         <{: w^ a w^ b w^ c :}h a b c ;> ;

   This example creates a home location with three cells on the heap,
and returns the addresses of the three locations and the address of the
home location.  This address can be used to 'free' the home location
when it is no longer needed.

'<{:' ( -- hmaddr u latest latestnt wid 0  ) gforth-experimental "start-homelocation"
   starts a home location

';>' ( --  ) gforth-experimental "end-homelocation"
   end using a home location

6.22.2 Standard Forth locals
----------------------------

The Forth-2012 standard defines a syntax for locals is restricted
version of Gforth's locals:

   * Locals can only be cell-sized values (no type specifiers are
     allowed).
   * Locals can be defined only outside control structures.
   * Only one locals definition per definition is allowed.
   * Locals can interfere with explicit usage of the return stack.  For
     the exact (and long) rules, see the standard.  If you don't use
     return stack accessing words in a definition using locals, you will
     be all right.  The purpose of this rule is to make locals
     implementation on the return stack easier.
   * The whole locals definition must be in one line.

   The Standard Forth locals wordset itself consists of two words: '{:'
and:

'(local)' ( addr u --  ) local "paren-local-paren"

   The ANS Forth locals extension wordset defines a syntax using
'locals|', but it is so awful that we strongly recommend not to use it.
We have implemented this syntax to make porting to Gforth easy, but do
not document it here.  The problem with this syntax is that the locals
are defined in an order reversed with respect to the standard stack
comment notation, making programs harder to read, and easier to misread
and miswrite.  The only merit of this syntax is that it is easy to
implement using the ANS Forth locals wordset, but then, so is the '{:'
syntax.

6.23 Structures
===============

This section presents the structure package that comes with Gforth.  A
version of the package implemented in Standard Forth is available in
'compat/struct.fs'.  This package was inspired by a posting on
comp.lang.forth in 1989 (unfortunately I don't remember, by whom;
possibly John Hayes).  A version of this section has been published in
M. Anton Ertl, Yet Another Forth Structures Package
(https://www.complang.tuwien.ac.at/forth/objects/structs.html), Forth
Dimensions 19(3), pages 13--16.  Marcel Hendrix provided helpful
comments.

6.23.1 Why explicit structure support?
--------------------------------------

If we want to use a structure containing several fields, we could simply
reserve memory for it, and access the fields using address arithmetic
(*note Address arithmetic::).  As an example, consider a structure with
the following fields

'a'
     is a float
'b'
     is a cell
'c'
     is a float

   Given the (float-aligned) base address of the structure we get the
address of the field

'a'
     without doing anything further.
'b'
     with 'float+'
'c'
     with 'float+ cell+ faligned'

   It is easy to see that this can become quite tiring.

   Moreover, it is not very readable, because seeing a 'cell+' tells us
neither which kind of structure is accessed nor what field is accessed;
we have to somehow infer the kind of structure, and then look up in the
documentation, which field of that structure corresponds to that offset.

   Finally, this kind of address arithmetic also causes maintenance
troubles: If you add or delete a field somewhere in the middle of the
structure, you have to find and change all computations for the fields
afterwards.

   So, instead of using 'cell+' and friends directly, how about storing
the offsets in constants:

     0 constant a-offset
     0 float+ constant b-offset
     0 float+ cell+ faligned c-offset

   Now we can get the address of field 'x' with 'x-offset +'.  This is
much better in all respects.  Of course, you still have to change all
later offset definitions if you add a field.  You can fix this by
declaring the offsets in the following way:

     0 constant a-offset
     a-offset float+ constant b-offset
     b-offset cell+ faligned constant c-offset

   Since we always use the offsets with '+', we could use a defining
word 'cfield' that includes the '+' in the action of the defined word:

     : cfield ( n "name" -- )
         create ,
     does> ( name execution: addr1 -- addr2 )
         @ + ;

     0 cfield a
     0 a float+ cfield b
     0 b cell+ faligned cfield c

   Instead of 'x-offset +', we now simply write 'x'.

   The structure field words now can be used quite nicely.  However,
their definition is still a bit cumbersome: We have to repeat the name,
the information about size and alignment is distributed before and after
the field definitions etc.  The structure package presented here
addresses these problems.

6.23.2 Structure Usage
----------------------

You can define a structure for a (data-less) linked list with:
     struct
         cell% field list-next
     end-struct list%

   With the address of the list node on the stack, you can compute the
address of the field that contains the address of the next node with
'list-next'.  E.g., you can determine the length of a list with:

     : list-length ( list -- n )
     \ "list" is a pointer to the first element of a linked list
     \ "n" is the length of the list
         0 BEGIN ( list1 n1 )
             over
         WHILE ( list1 n1 )
             1+ swap list-next @ swap
         REPEAT
         nip ;

   You can reserve memory for a list node in the dictionary with 'list%
%allot', which leaves the address of the list node on the stack.  For
the equivalent allocation on the heap you can use 'list% %alloc' (or,
for an 'allocate'-like stack effect (i.e., with ior), use 'list%
%allocate').  You can get the the size of a list node with 'list% %size'
and its alignment with 'list% %alignment'.

   Note that in Standard Forth the body of a 'create'd word is 'aligned'
but not necessarily 'faligned'; therefore, if you do a:

     create _name_ foo% %allot drop

then the memory alloted for 'foo%' is guaranteed to start at the body of
'_name_' only if 'foo%' contains only character, cell and double fields.
Therefore, if your structure contains floats, better use

     foo% %allot constant _name_

   You can include a structure 'foo%' as a field of another structure,
like this:
     struct
     ...
         foo% field ...
     ...
     end-struct ...

   Instead of starting with an empty structure, you can extend an
existing structure.  E.g., a plain linked list without data, as defined
above, is hardly useful; You can extend it to a linked list of integers,
like this:(1)

     list%
         cell% field intlist-int
     end-struct intlist%

   'intlist%' is a structure with two fields: 'list-next' and
'intlist-int'.

   You can specify an array type containing _n_ elements of type 'foo%'
like this:

     foo% _n_ *

   You can use this array type in any place where you can use a normal
type, e.g., when defining a 'field', or with '%allot'.

   The first field is at the base address of a structure and the word
for this field (e.g., 'list-next') actually does not change the address
on the stack.  You may be tempted to leave it away in the interest of
run-time and space efficiency.  This is not necessary, because the
structure package optimizes this case: If you compile a first-field
words, no code is generated.  So, in the interest of readability and
maintainability you should include the word for the field when accessing
the field.

   ---------- Footnotes ----------

   (1) This feature is also known as _extended records_.  It is the main
innovation in the Oberon language; in other words, adding this feature
to Modula-2 led Wirth to create a new language, write a new compiler
etc.  Adding this feature to Forth just required a few lines of code.

6.23.3 Structure Naming Convention
----------------------------------

The field names that come to (my) mind are often quite generic, and, if
used, would cause frequent name clashes.  E.g., many structures probably
contain a 'counter' field.  The structure names that come to (my) mind
are often also the logical choice for the names of words that create
such a structure.

   Therefore, I have adopted the following naming conventions:

   * The names of fields are of the form '_struct_-_field_', where
     '_struct_' is the basic name of the structure, and '_field_' is the
     basic name of the field.  You can think of field words as
     converting the (address of the) structure into the (address of the)
     field.

   * The names of structures are of the form '_struct_%', where
     '_struct_' is the basic name of the structure.

   This naming convention does not work that well for fields of extended
structures; e.g., the integer list structure has a field 'intlist-int',
but has 'list-next', not 'intlist-next'.

6.23.4 Structure Implementation
-------------------------------

The central idea in the implementation is to pass the data about the
structure being built on the stack, not in some global variable.
Everything else falls into place naturally once this design decision is
made.

   The type description on the stack is of the form _align size_.
Keeping the size on the top-of-stack makes dealing with arrays very
simple.

   'field' is a defining word that uses 'Create' and 'DOES>'.  The body
of the field contains the offset of the field, and the normal 'DOES>'
action is simply:

     @ +

i.e., add the offset to the address, giving the stack effect addr1 --
addr2 for a field.

   This simple structure is slightly complicated by the optimization for
fields with offset 0, which requires a different 'DOES>'-part (because
we cannot rely on there being something on the stack if such a field is
invoked during compilation).  Therefore, we put the different
'DOES>'-parts in separate words, and decide which one to invoke based on
the offset.  For a zero offset, the field is basically a noop; it is
immediate, and therefore no code is generated when it is compiled.

6.23.5 Structure Glossary
-------------------------

'%align' ( align size --  ) gforth-0.4 "%align"
   Align the data space pointer to the alignment ALIGN.

'%alignment' ( align size -- align  ) gforth-0.4 "%alignment"
   The alignment of the structure.

'%alloc' ( align size -- addr  ) gforth-0.4 "%alloc"
   Allocate SIZE address units with alignment ALIGN, giving a data block
at ADDR; 'throw' an ior code if not successful.

'%allocate' ( align size -- addr ior  ) gforth-0.4 "%allocate"
   Allocate SIZE address units with alignment ALIGN, similar to
'allocate'.

'%allot' ( align size -- addr  ) gforth-0.4 "%allot"
   Allot SIZE address units of data space with alignment ALIGN; the
resulting block of data is found at ADDR.

'cell%' ( -- align size  ) gforth-0.4 "cell%"

'char%' ( -- align size  ) gforth-0.4 "char%"

'dfloat%' ( -- align size  ) gforth-0.4 "dfloat%"

'double%' ( -- align size  ) gforth-0.4 "double%"

'end-struct' ( align size "name" --  ) gforth-0.2 "end-struct"
   Define a structure/type descriptor NAME with alignment ALIGN and size
SIZE1 (SIZE rounded up to be a multiple of ALIGN).
'name' execution: -- ALIGN SIZE1

'field' ( align1 offset1 align size "name" --  align2 offset2  ) gforth-0.2 "field"
   Create a field NAME with offset OFFSET1, and the type given by ALIGN
SIZE.  OFFSET2 is the offset of the next field, and ALIGN2 is the
alignment of all fields.
'name' execution: ADDR1 -- ADDR2.
ADDR2=ADDR1+OFFSET1

'float%' ( -- align size  ) gforth-0.4 "float%"

'sfloat%' ( -- align size  ) gforth-0.4 "sfloat%"

'%size' ( align size -- size  ) gforth-0.4 "%size"
   The size of the structure.

'struct' ( -- align size  ) gforth-0.2 "struct"
   An empty structure, used to start a structure definition.

6.23.6 Forth200x Structures
---------------------------

The Forth 2012 standard defines a slightly less convenient form of
structures.  In general (when using 'field+', you have to perform the
alignment yourself, but there are a number of convenience words (e.g.,
'field:') that include alignment.

   A typical usage example is:

     0
       field:                   s-a
       faligned 2 floats +field s-b
     constant s-struct

   An alternative way of writing this structure is:

     begin-structure s-struct
       field:                   s-a
       faligned 2 floats +field s-b
     end-structure

   You can define a structure that has the same fields and additional
fields as follows:

     s-struct
       cfield: t-c
       cfield: t-d
     constant t-struct

   or alternatively

     s-struct extend-structure t-struct
       cfield: t-c
       cfield: t-d
     end-structure

'begin-structure' ( "name" -- struct-sys 0  ) facility-ext "begin-structure"

'extend-structure' ( n "name" -- struct-sys n  ) gforth-1.0 "extend-structure"
   Start a new structure name as extension of an existing structure with
size n.

'end-structure' ( struct-sys +n --  ) facility-ext "end-structure"
   end a structure started wioth 'begin-structure'

'+field' ( noffset1 nsize "name" -- noffset2  ) facility-ext "plus-field"
   Defining word; defines name '( addr1 -- addr2 )', where addr2 is
addr1+noffset1.  noffset2 is noffset1+nsize.

'cfield:' ( u1 "name" -- u2  ) facility-ext "c-field-colon"
   Define a char-sized field

'field:' ( u1 "name" -- u2  ) facility-ext "field-colon"
   Define an aligned cell-sized field

'2field:' ( u1 "name" -- u2  ) gforth-0.7 "two-field-colon"
   Define an aligned double-cell-sized field

'ffield:' ( u1 "name" -- u2  ) floating-ext "f-field-colon"
   Define a faligned float-sized field

'sffield:' ( u1 "name" -- u2  ) floating-ext "s-f-field-colon"
   Define a sfaligned sfloat-sized field

'dffield:' ( u1 "name" -- u2  ) floating-ext "d-f-field-colon"
   Define a dfaligned dfloat-sized field

'wfield:' ( u1 "name" -- u2  ) gforth-1.0 "w-field-colon"
   Define a naturally aligned field for a 16-bit value.

'lfield:' ( u1 "name" -- u2  ) gforth-1.0 "l-field-colon"
   Define a naturally aligned field for a 32-bit value.

'xfield:' ( u1 "name" -- u2  ) gforth-1.0 "x-field-colon"
   Define a naturally aligned field for a 64-bit-value.

6.24 Object-oriented Forth
==========================

Gforth comes with three packages for object-oriented programming:
'objects.fs', 'oof.fs', and 'mini-oof.fs'; none of them is preloaded, so
you have to 'include' them before use.  The most important differences
between these packages (and others) are discussed in *note Comparison
with other object models::.  All packages are written in Standard Forth
and can be used with any other Standard Forth.

6.24.1 Why object-oriented programming?
---------------------------------------

Often we have to deal with several data structures (_objects_), that
have to be treated similarly in some respects, but differently in
others.  Graphical objects are the textbook example: circles, triangles,
dinosaurs, icons, and others, and we may want to add more during program
development.  We want to apply some operations to any graphical object,
e.g., 'draw' for displaying it on the screen.  However, 'draw' has to do
something different for every kind of object.

   We could implement 'draw' as a big 'CASE' control structure that
executes the appropriate code depending on the kind of object to be
drawn.  This would be not be very elegant, and, moreover, we would have
to change 'draw' every time we add a new kind of graphical object (say,
a spaceship).

   What we would rather do is: When defining spaceships, we would tell
the system: "Here's how you 'draw' a spaceship; you figure out the
rest".

   This is the problem that all systems solve that (rightfully) call
themselves object-oriented; the object-oriented packages presented here
solve this problem (and not much else).

6.24.2 Object-Oriented Terminology
----------------------------------

This section is mainly for reference, so you don't have to understand
all of it right away.  The terminology is mainly Smalltalk-inspired.  In
short:

_class_
     a data structure definition with some extras.

_object_
     an instance of the data structure described by the class
     definition.

_instance variables_
     fields of the data structure.

_selector_
     (or _method selector_) a word (e.g., 'draw') that performs an
     operation on a variety of data structures (classes).  A selector
     describes _what_ operation to perform.  In C++ terminology: a
     (pure) virtual function.

_method_
     the concrete definition that performs the operation described by
     the selector for a specific class.  A method specifies _how_ the
     operation is performed for a specific class.

_selector invocation_
     a call of a selector.  One argument of the call (the TOS
     (top-of-stack)) is used for determining which method is used.  In
     Smalltalk terminology: a message (consisting of the selector and
     the other arguments) is sent to the object.

_receiving object_
     the object used for determining the method executed by a selector
     invocation.  In the 'objects.fs' model, it is the object that is on
     the TOS when the selector is invoked.  (_Receiving_ comes from the
     Smalltalk _message_ terminology.)

_child class_
     a class that has (_inherits_) all properties (instance variables,
     selectors, methods) from a _parent class_.  In Smalltalk
     terminology: The subclass inherits from the superclass.  In C++
     terminology: The derived class inherits from the base class.

6.24.3 The 'objects.fs' model
-----------------------------

This section describes the 'objects.fs' package.  This material also has
been published in M. Anton Ertl, 'Yet Another Forth Objects Package
(https://www.complang.tuwien.ac.at/forth/objects/objects.html)', Forth
Dimensions 19(2), pages 37--43.

   This section assumes that you have read *note Structures::.

   The techniques on which this model is based have been used to
implement the parser generator, Gray, and have also been used in Gforth
for implementing the various flavours of word lists (hashed or not,
case-sensitive or not, special-purpose word lists for locals etc.).

   Marcel Hendrix provided helpful comments on this section.

6.24.3.1 Properties of the 'objects.fs' model
.............................................

   * It is straightforward to pass objects on the stack.  Passing
     selectors on the stack is a little less convenient, but possible.

   * Objects are just data structures in memory, and are referenced by
     their address.  You can create words for objects with normal
     defining words like 'constant'.  Likewise, there is no difference
     between instance variables that contain objects and those that
     contain other data.

   * Late binding is efficient and easy to use.

   * It avoids parsing, and thus avoids problems with state-smartness
     and reduced extensibility; for convenience there are a few parsing
     words, but they have non-parsing counterparts.  There are also a
     few defining words that parse.  This is hard to avoid, because all
     standard defining words parse (except ':noname'); however, such
     words are not as bad as many other parsing words, because they are
     not state-smart.

   * It does not try to incorporate everything.  It does a few things
     and does them well (IMO). In particular, this model was not
     designed to support information hiding (although it has features
     that may help); you can use a separate package for achieving this.

   * It is layered; you don't have to learn and use all features to use
     this model.  Only a few features are necessary (*note Basic Objects
     Usage::, *note The Objects base class::, *note Creating
     objects::.), the others are optional and independent of each other.

   * An implementation in Standard Forth is available.

6.24.3.2 Basic 'objects.fs' Usage
.................................

You can define a class for graphical objects like this:

     object class \ "object" is the parent class
       selector draw ( x y graphical -- )
     end-class graphical

   This code defines a class 'graphical' with an operation 'draw'.  We
can perform the operation 'draw' on any 'graphical' object, e.g.:

     100 100 t-rex draw

where 't-rex' is a word (say, a constant) that produces a graphical
object.

   How do we create a graphical object?  With the present definitions,
we cannot create a useful graphical object.  The class 'graphical'
describes graphical objects in general, but not any concrete graphical
object type (C++ users would call it an _abstract class_); e.g., there
is no method for the selector 'draw' in the class 'graphical'.

   For concrete graphical objects, we define child classes of the class
'graphical', e.g.:

     graphical class \ "graphical" is the parent class
       cell% field circle-radius

     :noname ( x y circle -- )
       circle-radius @ draw-circle ;
     overrides draw

     :noname ( n-radius circle -- )
       circle-radius ! ;
     overrides construct

     end-class circle

   Here we define a class 'circle' as a child of 'graphical', with field
'circle-radius' (which behaves just like a field (*note Structures::);
it defines (using 'overrides') new methods for the selectors 'draw' and
'construct' ('construct' is defined in 'object', the parent class of
'graphical').

   Now we can create a circle on the heap (i.e., 'allocate'd memory)
with:

     50 circle heap-new constant my-circle

'heap-new' invokes 'construct', thus initializing the field
'circle-radius' with 50.  We can draw this new circle at (100,100) with:

     100 100 my-circle draw

   Note: You can only invoke a selector if the object on the TOS (the
receiving object) belongs to the class where the selector was defined or
one of its descendents; e.g., you can invoke 'draw' only for objects
belonging to 'graphical' or its descendents (e.g., 'circle').
Immediately before 'end-class', the search order has to be the same as
immediately after 'class'.

6.24.3.3 The 'object.fs' base class
...................................

When you define a class, you have to specify a parent class.  So how do
you start defining classes?  There is one class available from the
start: 'object'.  It is ancestor for all classes and so is the only
class that has no parent.  It has two selectors: 'construct' and
'print'.

6.24.3.4 Creating objects
.........................

You can create and initialize an object of a class on the heap with
'heap-new' ( ...  class -- object ) and in the dictionary (allocation
with 'allot') with 'dict-new' ( ...  class -- object ).  Both words
invoke 'construct', which consumes the stack items indicated by "..."
above.

   If you want to allocate memory for an object yourself, you can get
its alignment and size with 'class-inst-size 2@' ( class -- align size ).
Once you have memory for an object, you can initialize it with
'init-object' ( ...  class object -- ); 'construct' does only a part of
the necessary work.

6.24.3.5 Object-Oriented Programming Style
..........................................

This section is not exhaustive.

   In general, it is a good idea to ensure that all methods for the same
selector have the same stack effect: when you invoke a selector, you
often have no idea which method will be invoked, so, unless all methods
have the same stack effect, you will not know the stack effect of the
selector invocation.

   One exception to this rule is methods for the selector 'construct'.
We know which method is invoked, because we specify the class to be
constructed at the same place.  Actually, I defined 'construct' as a
selector only to give the users a convenient way to specify
initialization.  The way it is used, a mechanism different from selector
invocation would be more natural (but probably would take more code and
more space to explain).

6.24.3.6 Class Binding
......................

Normal selector invocations determine the method at run-time depending
on the class of the receiving object.  This run-time selection is called
late binding.

   Sometimes it's preferable to invoke a different method.  For example,
you might want to use the simple method for 'print'ing 'object's instead
of the possibly long-winded 'print' method of the receiver class.  You
can achieve this by replacing the invocation of 'print' with:

     [bind] object print

in compiled code or:

     bind object print

in interpreted code.  Alternatively, you can define the method with a
name (e.g., 'print-object'), and then invoke it through the name.  Class
binding is just a (often more convenient) way to achieve the same
effect; it avoids name clutter and allows you to invoke methods directly
without naming them first.

   A frequent use of class binding is this: When we define a method for
a selector, we often want the method to do what the selector does in the
parent class, and a little more.  There is a special word for this
purpose: '[parent]'; '[parent] _selector_' is equivalent to '[bind]
_parent selector_', where '_parent_' is the parent class of the current
class.  E.g., a method definition might look like:

     :noname
       dup [parent] foo \ do parent's foo on the receiving object
       ... \ do some more
     ; overrides foo

   In 'Object-oriented programming in ANS Forth' (Forth Dimensions,
March 1997), Andrew McKewan presents class binding as an optimization
technique.  I recommend not using it for this purpose unless you are in
an emergency.  Late binding is pretty fast with this model anyway, so
the benefit of using class binding is small; the cost of using class
binding where it is not appropriate is reduced maintainability.

   While we are at programming style questions: You should bind
selectors only to ancestor classes of the receiving object.  E.g., say,
you know that the receiving object is of class 'foo' or its descendents;
then you should bind only to 'foo' and its ancestors.

6.24.3.7 Method conveniences
............................

In a method you usually access the receiving object pretty often.  If
you define the method as a plain colon definition (e.g., with
':noname'), you may have to do a lot of stack gymnastics.  To avoid
this, you can define the method with 'm: ... ;m'.  E.g., you could
define the method for 'draw'ing a 'circle' with

     m: ( x y circle -- )
       ( x y ) this circle-radius @ draw-circle ;m

   When this method is executed, the receiver object is removed from the
stack; you can access it with 'this' (admittedly, in this example the
use of 'm: ... ;m' offers no advantage).  Note that I specify the stack
effect for the whole method (i.e.  including the receiver object), not
just for the code between 'm:' and ';m'.  You cannot use 'exit' in
'm:...;m'; instead, use 'exitm'.(1)

   You will frequently use sequences of the form 'this _field_' (in the
example above: 'this circle-radius').  If you use the field only in this
way, you can define it with 'inst-var' and eliminate the 'this' before
the field name.  E.g., the 'circle' class above could also be defined
with:

     graphical class
       cell% inst-var radius

     m: ( x y circle -- )
       radius @ draw-circle ;m
     overrides draw

     m: ( n-radius circle -- )
       radius ! ;m
     overrides construct

     end-class circle

   'radius' can only be used in 'circle' and its descendent classes and
inside 'm:...;m'.

   You can also define fields with 'inst-value', which is to 'inst-var'
what 'value' is to 'variable'.  You can change the value of such a field
with '[to-inst]'.  E.g., we could also define the class 'circle' like
this:

     graphical class
       inst-value radius

     m: ( x y circle -- )
       radius draw-circle ;m
     overrides draw

     m: ( n-radius circle -- )
       [to-inst] radius ;m
     overrides construct

     end-class circle

   ---------- Footnotes ----------

   (1) Moreover, for any word that calls 'catch' and was defined before
loading 'objects.fs', you have to redefine it like I redefined 'catch':
': catch this >r catch r> to-this ;'

6.24.3.8 Classes and Scoping
............................

Inheritance is frequent, unlike structure extension.  This exacerbates
the problem with the field name convention (*note Structure Naming
Convention::): One always has to remember in which class the field was
originally defined; changing a part of the class structure would require
changes for renaming in otherwise unaffected code.

   To solve this problem, I added a scoping mechanism (which was not in
my original charter): A field defined with 'inst-var' (or 'inst-value')
is visible only in the class where it is defined and in the descendent
classes of this class.  Using such fields only makes sense in
'm:'-defined methods in these classes anyway.

   This scoping mechanism allows us to use the unadorned field name,
because name clashes with unrelated words become much less likely.

   Once we have this mechanism, we can also use it for controlling the
visibility of other words: All words defined after 'protected' are
visible only in the current class and its descendents.  'public'
restores the compilation (i.e.  'current') word list that was in effect
before.  If you have several 'protected's without an intervening
'public' or 'set-current', 'public' will restore the compilation word
list in effect before the first of these 'protected's.

6.24.3.9 Dividing classes
.........................

You may want to do the definition of methods separate from the
definition of the class, its selectors, fields, and instance variables,
i.e., separate the implementation from the definition.  You can do this
in the following way:

     graphical class
       inst-value radius
     end-class circle

     ... \ do some other stuff

     circle methods \ now we are ready

     m: ( x y circle -- )
       radius draw-circle ;m
     overrides draw

     m: ( n-radius circle -- )
       [to-inst] radius ;m
     overrides construct

     end-methods

   You can use several 'methods'...'end-methods' sections.  The only
things you can do to the class in these sections are: defining methods,
and overriding the class's selectors.  You must not define new selectors
or fields.

   Note that you often have to override a selector before using it.  In
particular, you usually have to override 'construct' with a new method
before you can invoke 'heap-new' and friends.  E.g., you must not create
a circle before the 'overrides construct' sequence in the example above.

6.24.3.10 Object Interfaces
...........................

In this model you can only call selectors defined in the class of the
receiving objects or in one of its ancestors.  If you call a selector
with a receiving object that is not in one of these classes, the result
is undefined; if you are lucky, the program crashes immediately.

   Now consider the case when you want to have a selector (or several)
available in two classes: You would have to add the selector to a common
ancestor class, in the worst case to 'object'.  You may not want to do
this, e.g., because someone else is responsible for this ancestor class.

   The solution for this problem is interfaces.  An interface is a
collection of selectors.  If a class implements an interface, the
selectors become available to the class and its descendents.  A class
can implement an unlimited number of interfaces.  For the problem
discussed above, we would define an interface for the selector(s), and
both classes would implement the interface.

   As an example, consider an interface 'storage' for writing objects to
disk and getting them back, and a class 'foo' that implements it.  The
code would look like this:

     interface
       selector write ( file object -- )
       selector read1 ( file object -- )
     end-interface storage

     bar class
       storage implementation

     ... overrides write
     ... overrides read1
     ...
     end-class foo

(I would add a word 'read' ( file -- object ) that uses 'read1'
internally, but that's beyond the point illustrated here.)

   Note that you cannot use 'protected' in an interface; and of course
you cannot define fields.

   In the Neon model, all selectors are available for all classes;
therefore it does not need interfaces.  The price you pay in this model
is slower late binding, and therefore, added complexity to avoid late
binding.

6.24.3.11 'objects.fs' Implementation
.....................................

An object is a piece of memory, like one of the data structures
described with 'struct...end-struct'.  It has a field 'object-map' that
points to the method map for the object's class.

   The _method map_(1) is an array that contains the execution tokens
(xts) of the methods for the object's class.  Each selector contains an
offset into a method map.

   'selector' is a defining word that uses 'CREATE' and 'DOES>'.  The
body of the selector contains the offset; the 'DOES>' action for a class
selector is, basically:

     ( object addr ) @ over object-map @ + @ execute

   Since 'object-map' is the first field of the object, it does not
generate any code.  As you can see, calling a selector has a small,
constant cost.

   A class is basically a 'struct' combined with a method map.  During
the class definition the alignment and size of the class are passed on
the stack, just as with 'struct's, so 'field' can also be used for
defining class fields.  However, passing more items on the stack would
be inconvenient, so 'class' builds a data structure in memory, which is
accessed through the variable 'current-interface'.  After its definition
is complete, the class is represented on the stack by a pointer (e.g.,
as parameter for a child class definition).

   A new class starts off with the alignment and size of its parent, and
a copy of the parent's method map.  Defining new fields extends the size
and alignment; likewise, defining new selectors extends the method map.
'overrides' just stores a new xt in the method map at the offset given
by the selector.

   Class binding just gets the xt at the offset given by the selector
from the class's method map and 'compile,'s (in the case of '[bind]')
it.

   I implemented 'this' as a 'value'.  At the start of an 'm:...;m'
method the old 'this' is stored to the return stack and restored at the
end; and the object on the TOS is stored 'TO this'.  This technique has
one disadvantage: If the user does not leave the method via ';m', but
via 'throw' or 'exit', 'this' is not restored (and 'exit' may crash).
To deal with the 'throw' problem, I have redefined 'catch' to save and
restore 'this'; the same should be done with any word that can catch an
exception.  As for 'exit', I simply forbid it (as a replacement, there
is 'exitm').

   'inst-var' is just the same as 'field', with a different 'DOES>'
action:
     @ this +
   Similar for 'inst-value'.

   Each class also has a word list that contains the words defined with
'inst-var' and 'inst-value', and its protected words.  It also has a
pointer to its parent.  'class' pushes the word lists of the class and
all its ancestors onto the search order stack, and 'end-class' drops
them.

   An interface is like a class without fields, parent and protected
words; i.e., it just has a method map.  If a class implements an
interface, its method map contains a pointer to the method map of the
interface.  The positive offsets in the map are reserved for class
methods, therefore interface map pointers have negative offsets.
Interfaces have offsets that are unique throughout the system, unlike
class selectors, whose offsets are only unique for the classes where the
selector is available (invokable).

   This structure means that interface selectors have to perform one
indirection more than class selectors to find their method.  Their body
contains the interface map pointer offset in the class method map, and
the method offset in the interface method map.  The 'does>' action for
an interface selector is, basically:

     ( object selector-body )
     2dup selector-interface @ ( object selector-body object interface-offset )
     swap object-map @ + @ ( object selector-body map )
     swap selector-offset @ + @ execute

   where 'object-map' and 'selector-offset' are first fields and
generate no code.

   As a concrete example, consider the following code:

     interface
       selector if1sel1
       selector if1sel2
     end-interface if1

     object class
       if1 implementation
       selector cl1sel1
       cell% inst-var cl1iv1

     ' m1 overrides construct
     ' m2 overrides if1sel1
     ' m3 overrides if1sel2
     ' m4 overrides cl1sel2
     end-class cl1

     create obj1 object dict-new drop
     create obj2 cl1    dict-new drop

   The data structure created by this code (including the data structure
for 'object') is shown in the figure (objects-implementation.eps),
assuming a cell size of 4.

   ---------- Footnotes ----------

   (1) This is Self terminology; in C++ terminology: virtual function
table.

6.24.3.12 'objects.fs' Glossary
...............................

'bind' ( ... "class" "selector" -- ...  ) objects "bind"
   Execute the method for SELECTOR in CLASS.

'<bind>' ( class selector-xt -- xt  ) objects "<bind>"
   XT is the method for the selector SELECTOR-XT in CLASS.

'bind'' ( "class" "selector" -- xt  ) objects "bind"'
   XT is the method for SELECTOR in CLASS.

'[bind]' ( compile-time: "class" "selector" -- ; run-time: ... object -- ...  ) objects "[bind]"
   Compile the method for SELECTOR in CLASS.

'class' ( parent-class -- align offset  ) objects "class"
   Start a new class definition as a child of PARENT-CLASS.  ALIGN
OFFSET are for use by FIELD etc.

'class->map' ( class -- map  ) objects "class->map"
   MAP is the pointer to CLASS's method map; it points to the place in
the map to which the selector offsets refer (i.e., where OBJECT-MAPs
point to).

'class-inst-size' ( class -- addr  ) objects "class-inst-size"
   Give the size specification for an instance (i.e.  an object) of
CLASS; used as 'class-inst-size 2 ( class -- align size )'.

'class-override!' ( xt sel-xt class-map --  ) objects "class-override!"
   XT is the new method for the selector SEL-XT in CLASS-MAP.

'class-previous' ( class --  ) objects "class-previous"
   Drop CLASS's wordlists from the search order.  No checking is made
whether CLASS's wordlists are actually on the search order.

'class>order' ( class --  ) objects "class>order"
   Add CLASS's wordlists to the head of the search-order.

'construct' ( ... object --  ) objects "construct"
   Initialize the data fields of OBJECT.  The method for the class
OBJECT just does nothing: '( object -- )'.

'current'' ( "selector" -- xt  ) objects "current"'
   XT is the method for SELECTOR in the current class.

'[current]' ( compile-time: "selector" -- ; run-time: ... object -- ...  ) objects "[current]"
   Compile the method for SELECTOR in the current class.

'current-interface' ( -- addr  ) objects "current-interface"
   Variable: contains the class or interface currently being defined.

'dict-new' ( ... class -- object  ) objects "dict-new"
   'allot' and initialize an object of class CLASS in the dictionary.

'end-class' ( align offset "name" --  ) objects "end-class"
   NAME execution: '-- class'
End a class definition.  The resulting class is CLASS.

'end-class-noname' ( align offset -- class  ) objects "end-class-noname"
   End a class definition.  The resulting class is CLASS.

'end-interface' ( "name" --  ) objects "end-interface"
   'name' execution: '-- interface'
End an interface definition.  The resulting interface is INTERFACE.

'end-interface-noname' ( -- interface  ) objects "end-interface-noname"
   End an interface definition.  The resulting interface is INTERFACE.

'end-methods' ( --  ) objects "end-methods"
   Switch back from defining methods of a class to normal mode
(currently this just restores the old search order).

'exitm' ( --  ) objects "exitm"
   'exit' from a method; restore old 'this'.

'heap-new' ( ... class -- object  ) objects "heap-new"
   'allocate' and initialize an object of class CLASS.

'implementation' ( interface --  ) objects "implementation"
   The current class implements INTERFACE.  I.e., you can use all
selectors of the interface in the current class and its descendents.

'init-object' ( ... class object --  ) objects "init-object"
   Initialize a chunk of memory (OBJECT) to an object of class CLASS;
then performs 'construct'.

'inst-value' ( align1 offset1 "name" -- align2 offset2  ) objects "inst-value"
   NAME execution: '-- w'
W is the value of the field NAME in 'this' object.

'inst-var' ( align1 offset1 align size "name" -- align2 offset2  ) objects "inst-var"
   NAME execution: '-- addr'
ADDR is the address of the field NAME in 'this' object.

'interface' ( --  ) objects "interface"
   Start an interface definition.

'm:' ( -- xt colon-sys; run-time: object --  ) objects "m:"
   Start a method definition; OBJECT becomes new 'this'.

':m' ( "name" -- xt; run-time: object --  ) objects ":m"
   Start a named method definition; OBJECT becomes new 'this'.  Has to
be ended with ';m'.

';m' ( colon-sys --; run-time: --  ) objects ";m"
   End a method definition; restore old 'this'.

'method' ( xt "name" --  ) objects "method"
   'name' execution: '... object -- ...'
Create selector NAME and makes XT its method in the current class.

'methods' ( class --  ) objects "methods"
   Makes CLASS the current class.  This is intended to be used for
defining methods to override selectors; you cannot define new fields or
selectors.

'object' ( -- class  ) objects "object"
   the ancestor of all classes.

'overrides' ( xt "selector" --  ) objects "overrides"
   replace default method for SELECTOR in the current class with XT.
'overrides' must not be used during an interface definition.

'[parent]' ( compile-time: "selector" -- ; run-time: ... object -- ...  ) objects "[parent]"
   Compile the method for SELECTOR in the parent of the current class.

'print' ( object --  ) objects "print"
   Print the object.  The method for the class OBJECT prints the address
of the object and the address of its class.

'protected' ( --  ) objects "protected"
   Set the compilation wordlist to the current class's wordlist

'public' ( --  ) objects "public"
   Restore the compilation wordlist that was in effect before the last
'protected' that actually changed the compilation wordlist.

'selector' ( "name" --  ) objects "selector"
   NAME execution: '... object -- ...'
Create selector NAME for the current class and its descendents; you can
set a method for the selector in the current class with 'overrides'.

'this' ( -- object  ) objects "this"
   the receiving object of the current method (aka active object).

'<to-inst>' ( w xt --  ) objects "<to-inst>"
   store W into the field XT in 'this' object.

'[to-inst]' ( compile-time: "name" -- ; run-time: w --  ) objects "[to-inst]"
   store W into field NAME in 'this' object.

'to-this' ( object --  ) objects "to-this"
   Set 'this' (used internally, but useful when debugging).

'xt-new' ( ... class xt -- object  ) objects "xt-new"
   Make a new object, using 'xt ( align size -- addr )' to get memory.

6.24.4 The 'oof.fs' model
-------------------------

This section describes the 'oof.fs' package.

   The package described in this section has been used in bigFORTH since
1991, and used for two large applications: a chromatographic system used
to create new medicaments, and a graphic user interface library (MINOS).

   You can find a description (in German) of 'oof.fs' in 'Object
oriented bigFORTH' by Bernd Paysan, published in 'Vierte Dimension'
10(2), 1994.

6.24.4.1 Properties of the 'oof.fs' model
.........................................

   * This model combines object oriented programming with information
     hiding.  It helps you writing large application, where scoping is
     necessary, because it provides class-oriented scoping.

   * Named objects, object pointers, and object arrays can be created,
     selector invocation uses the "object selector" syntax.  Selector
     invocation to objects and/or selectors on the stack is a bit less
     convenient, but possible.

   * Selector invocation and instance variable usage of the active
     object is straightforward, since both make use of the active
     object.

   * Late binding is efficient and easy to use.

   * State-smart objects parse selectors.  However, extensibility is
     provided using a (parsing) selector 'postpone' and a selector '''.

   * An implementation in Standard Forth is available.

6.24.4.2 Basic 'oof.fs' Usage
.............................

This section uses the same example as for 'objects' (*note Basic Objects
Usage::).

   You can define a class for graphical objects like this:

     object class graphical \ "object" is the parent class
       method draw ( x y -- )
     class;

   This code defines a class 'graphical' with an operation 'draw'.  We
can perform the operation 'draw' on any 'graphical' object, e.g.:

     100 100 t-rex draw

where 't-rex' is an object or object pointer, created with e.g.
'graphical : t-rex'.

   How do we create a graphical object?  With the present definitions,
we cannot create a useful graphical object.  The class 'graphical'
describes graphical objects in general, but not any concrete graphical
object type (C++ users would call it an _abstract class_); e.g., there
is no method for the selector 'draw' in the class 'graphical'.

   For concrete graphical objects, we define child classes of the class
'graphical', e.g.:

     graphical class circle \ "graphical" is the parent class
       cell var circle-radius
     how:
       : draw ( x y -- )
         circle-radius @ draw-circle ;

       : init ( n-radius -- )
         circle-radius ! ;
     class;

   Here we define a class 'circle' as a child of 'graphical', with a
field 'circle-radius'; it defines new methods for the selectors 'draw'
and 'init' ('init' is defined in 'object', the parent class of
'graphical').

   Now we can create a circle in the dictionary with:

     50 circle : my-circle

':' invokes 'init', thus initializing the field 'circle-radius' with 50.
We can draw this new circle at (100,100) with:

     100 100 my-circle draw

   Note: You can only invoke a selector if the receiving object belongs
to the class where the selector was defined or one of its descendents;
e.g., you can invoke 'draw' only for objects belonging to 'graphical' or
its descendents (e.g., 'circle').  The scoping mechanism will check if
you try to invoke a selector that is not defined in this class
hierarchy, so you'll get an error at compilation time.

6.24.4.3 The 'oof.fs' base class
................................

When you define a class, you have to specify a parent class.  So how do
you start defining classes?  There is one class available from the
start: 'object'.  You have to use it as ancestor for all classes.  It is
the only class that has no parent.  Classes are also objects, except
that they don't have instance variables; class manipulation such as
inheritance or changing definitions of a class is handled through
selectors of the class 'object'.

   'object' provides a number of selectors:

   * 'class' for subclassing, 'definitions' to add definitions later on,
     and 'class?' to get type informations (is the class a subclass of
     the class passed on the stack?).

     'object-class' ( "name" --  ) oof "object-class"

     'object-definitions' ( --  ) oof "object-definitions"

     'object-class?' ( o -- flag  ) oof "class-query"

   * 'init' and 'dispose' as constructor and destructor of the object.
     'init' is invocated after the object's memory is allocated, while
     'dispose' also handles deallocation.  Thus if you redefine
     'dispose', you have to call the parent's dispose with 'super
     dispose', too.

     'object-init' ( ... --  ) oof "object-init"

     'object-dispose' ( --  ) oof "object-dispose"

   * 'new', 'new[]', ':', 'ptr', 'asptr', and '[]' to create named and
     unnamed objects and object arrays or object pointers.

     'object-new' ( -- o  ) oof "object-new"

     'object-new[]' ( n -- o  ) oof "new-array"

     'object-:' ( "name" --  ) oof "define"

     'object-ptr' ( "name" --  ) oof "object-ptr"

     'object-asptr' ( o "name" --  ) oof "object-asptr"

     'object-[]' ( n "name" --  ) oof "array"

   * '::' and 'super' for explicit scoping.  You should use explicit
     scoping only for super classes or classes with the same set of
     instance variables.  Explicitly-scoped selectors use early binding.

     'object-::' ( "name" --  ) oof "scope"

     'object-super' ( "name" --  ) oof "object-super"

   * 'self' to get the address of the object

     'object-self' ( -- o  ) oof "object-self"

   * 'bind', 'bound', 'link', and 'is' to assign object pointers and
     instance defers.

     'object-bind' ( o "name" --  ) oof "object-bind"

     'object-bound' ( class addr "name" --  ) oof "object-bound"

     'object-link' ( "name" -- class addr  ) oof "object-link"

     'object-is' ( xt "name" --  ) oof "object-is"

   * ''' to obtain selector tokens, 'send' to invocate selectors form
     the stack, and 'postpone' to generate selector invocation code.

     'object-'' ( "name" -- xt  ) oof "tick"

     'object-postpone' ( "name" --  ) oof "object-postpone"

   * 'with' and 'endwith' to select the active object from the stack,
     and enable its scope.  Using 'with' and 'endwith' also allows you
     to create code using selector 'postpone' without being trapped by
     the state-smart objects.

     'object-with' ( o --  ) oof "object-with"

     'object-endwith' ( --  ) oof "object-endwith"

6.24.4.4 Class Declaration
..........................

   * Instance variables

     'var' ( size --  ) oof "var"
     Create an instance variable

   * Object pointers

     'ptr' ( --  ) oof "ptr"
     Create an instance pointer

     'asptr' ( class --  ) oof "asptr"
     Create an alias to an instance pointer, cast to another class.

   * Instance defers

     'defer' ( --  ) oof "defer"
     Create an instance defer

   * Method selectors

     'early' ( --  ) oof "early"
     Create a method selector for early binding.

     'method' ( --  ) oof "method"
     Create a method selector.

   * Class-wide variables

     'static' ( --  ) oof "static"
     Create a class-wide cell-sized variable.

   * End declaration

     'how:' ( --  ) oof "how-to"
     End declaration, start implementation

     'class;' ( --  ) oof "end-class"
     End class declaration or implementation

6.24.4.5 Class Implementation
.............................

6.24.5 The 'mini-oof.fs' model
------------------------------

Gforth's third object oriented Forth package is a 12-liner.  It uses a
mixture of the 'objects.fs' and the 'oof.fs' syntax, and reduces to the
bare minimum of features.  This is based on a posting of Bernd Paysan in
comp.lang.forth.

6.24.5.1 Basic 'mini-oof.fs' Usage
..................................

There is a base class ('class', which allocates one cell for the object
pointer) plus seven other words: to define a method, a variable, a
class; to end a class, to resolve binding, to allocate an object and to
compile a class method.

'object' ( -- a-addr  ) mini-oof "object"
   OBJECT is the base class of all objects.

'method' ( m v "name" -- m' v  ) mini-oof "method"
   Define a selector.

'var' ( m v size "name" -- m v'  ) mini-oof "var"
   Define a variable with SIZE bytes.

'class' ( class -- class selectors vars  ) mini-oof "class"
   Start the definition of a class.

'end-class' ( class selectors vars "name" --  ) mini-oof "end-class"
   End the definition of a class.

'defines' ( xt class "name" --  ) mini-oof "defines"
   Bind XT to the selector NAME in class CLASS.

'new' ( class -- o  ) mini-oof "new"
   Create a new incarnation of the class CLASS.

'::' ( class "name" --  ) mini-oof "colon-colon"
   Compile the method for the selector NAME of the class CLASS (not
immediate!).

6.24.5.2 Mini-OOF Example
.........................

A short example shows how to use this package.  This example, in
slightly extended form, is supplied as 'moof-exm.fs'

     object class
       method init
       method draw
     end-class graphical

   This code defines a class 'graphical' with an operation 'draw'.  We
can perform the operation 'draw' on any 'graphical' object, e.g.:

     100 100 t-rex draw

   where 't-rex' is an object or object pointer, created with e.g.
'graphical new Constant t-rex'.

   For concrete graphical objects, we define child classes of the class
'graphical', e.g.:

     graphical class
       cell var circle-radius
     end-class circle \ "graphical" is the parent class

     :noname ( x y -- )
       circle-radius @ draw-circle ; circle defines draw
     :noname ( r -- )
       circle-radius ! ; circle defines init

   There is no implicit init method, so we have to define one.  The
creation code of the object now has to call init explicitely.

     circle new Constant my-circle
     50 my-circle init

   It is also possible to add a function to create named objects with
automatic call of 'init', given that all objects have 'init' on the same
place:

     : new: ( .. o "name" -- )
         new dup Constant init ;
     80 circle new: large-circle

   We can draw this new circle at (100,100) with:

     100 100 my-circle draw

6.24.5.3 'mini-oof.fs' Implementation
.....................................

Object-oriented systems with late binding typically use a
"vtable"-approach: the first variable in each object is a pointer to a
table, which contains the methods as function pointers.  The vtable may
also contain other information.

   So first, let's declare selectors:

     : method ( m v "name" -- m' v ) Create  over , swap cell+ swap
       DOES> ( ... o -- ... ) @ over @ + @ execute ;

   During selector declaration, the number of selectors and instance
variables is on the stack (in address units).  'method' creates one
selector and increments the selector number.  To execute a selector, it
takes the object, fetches the vtable pointer, adds the offset, and
executes the method xt stored there.  Each selector takes the object it
is invoked with as top of stack parameter; it passes the parameters
(including the object) unchanged to the appropriate method which should
consume that object.

   Now, we also have to declare instance variables

     : var ( m v size "name" -- m v' ) Create  over , +
       DOES> ( o -- addr ) @ + ;

   As before, a word is created with the current offset.  Instance
variables can have different sizes (cells, floats, doubles, chars), so
all we do is take the size and add it to the offset.  If your machine
has alignment restrictions, put the proper 'aligned' or 'faligned'
before the variable, to adjust the variable offset.  That's why it is on
the top of stack.

   We need a starting point (the base object) and some syntactic sugar:

     Create object  1 cells , 2 cells ,
     : class ( class -- class selectors vars ) dup 2@ ;

   For inheritance, the vtable of the parent object has to be copied
when a new, derived class is declared.  This gives all the methods of
the parent class, which can be overridden, though.

     : end-class  ( class selectors vars "name" -- )
       Create  here >r , dup , 2 cells ?DO ['] noop , 1 cells +LOOP
       cell+ dup cell+ r> rot @ 2 cells /string move ;

   The first line creates the vtable, initialized with 'noop's.  The
second line is the inheritance mechanism, it copies the xts from the
parent vtable.

   We still have no way to define new methods, let's do that now:

     : defines ( xt class "name" -- ) ' >body @ + ! ;

   To allocate a new object, we need a word, too:

     : new ( class -- o )  here over @ allot swap over ! ;

   Sometimes derived classes want to access the method of the parent
object.  There are two ways to achieve this with Mini-OOF: first, you
could use named words, and second, you could look up the vtable of the
parent object.

     : :: ( class "name" -- ) ' >body @ + @ compile, ;

   Nothing can be more confusing than a good example, so here is one.
First let's declare a text object (called 'button'), that stores text
and position:

     object class
       cell var text
       cell var len
       cell var x
       cell var y
       method init
       method draw
     end-class button

Now, implement the two methods, 'draw' and 'init':

     :noname ( o -- )
      >r r@ x @ r@ y @ at-xy  r@ text @ r> len @ type ;
      button defines draw
     :noname ( addr u o -- )
      >r 0 r@ x ! 0 r@ y ! r@ len ! r> text ! ;
      button defines init

To demonstrate inheritance, we define a class 'bold-button', with no new
data and no new selectors:

     button class
     end-class bold-button

     : bold   27 emit ." [1m" ;
     : normal 27 emit ." [0m" ;

The class 'bold-button' has a different draw method to 'button', but the
new method is defined in terms of the draw method for 'button':

     :noname bold [ button :: draw ] normal ; bold-button defines draw

Finally, create two objects and apply selectors:

     button new Constant foo
     s" thin foo" foo init
     page
     foo draw
     bold-button new Constant bar
     s" fat bar" bar init
     1 bar y !
     bar draw

6.24.6 Mini-OOF2
----------------

Mini-OOF2 is very similar to Mini-OOF in many respects, but differs
significantly in a few aspects.  In particular, Mini-OOF2 has a current
object variable, and uses the primitives '>o' and 'o>' to manipulate
that object stack.  All method invocations and instance variable
accesses refer to the current object.

'>o' ( c-addr -- r:c-old ) new "to-o"
   Set the current object to C_ADDR, the previous current object is
pushed to the return stack

'o>' ( r:c-addr -- ) new "o-restore"
   Restore the previous current object from the return stack

   To ease passing an object pointer to method invocation or instance
variable accesses, the additional recognizer 'rec-moof2' is activated.

'rec-moof2' ( addr u -- xt translate-moof2 | notfound  ) mini-oof2 "rec-moof2"
   Very simplistic dot-parser, transforms '.'SELECTOR/IVAR to '>o'
SELECTOR/IVAR 'o>'.

   To assign methods to selectors, use XT CLASS 'is' SELECTOR, so no
'defines' necessary.  For early binding of methods, '[' CLASS '] defers'
SELECTOR is used, no need for '::'.

6.24.7 Comparison with other object models
------------------------------------------

Many object-oriented Forth extensions have been proposed ('A survey of
object-oriented Forths' (SIGPLAN Notices, April 1996) by Bradford J.
Rodriguez and W. F. S. Poehlman lists 17).  This section discusses the
relation of the object models described here to two well-known and two
closely-related (by the use of method maps) models.  Andras Zsoter
helped us with this section.

   The most popular model currently seems to be the Neon model (see
'Object-oriented programming in ANS Forth' (Forth Dimensions, March
1997) by Andrew McKewan) but this model has a number of limitations (1):

   * It uses a '_selector object_' syntax, which makes it unnatural to
     pass objects on the stack.

   * It requires that the selector parses the input stream (at compile
     time); this leads to reduced extensibility and to bugs that are
     hard to find.

   * It allows using every selector on every object; this eliminates the
     need for interfaces, but makes it harder to create efficient
     implementations.

   Another well-known publication is 'Object-Oriented Forth' (Academic
Press, London, 1987) by Dick Pountain.  However, it is not really about
object-oriented programming, because it hardly deals with late binding.
Instead, it focuses on features like information hiding and overloading
that are characteristic of modular languages like Ada (83).

   In Does late binding have to be slow?
(http://www.forth.org/oopf.html) (Forth Dimensions 18(1) 1996, pages
31-35) Andras Zsoter describes a model that makes heavy use of an active
object (like 'this' in 'objects.fs'): The active object is not only used
for accessing all fields, but also specifies the receiving object of
every selector invocation; you have to change the active object
explicitly with '{ ... }', whereas in 'objects.fs' it changes more or
less implicitly at 'm: ... ;m'.  Such a change at the method entry point
is unnecessary with Zsoter's model, because the receiving object is the
active object already.  On the other hand, the explicit change is
absolutely necessary in that model, because otherwise no one could ever
change the active object.  An Standard Forth implementation of this
model is available through <http://www.forth.org/oopf.html>.

   The 'oof.fs' model combines information hiding and overloading
resolution (by keeping names in various word lists) with object-oriented
programming.  It sets the active object implicitly on method entry, but
also allows explicit changing (with '>o...o>' or with 'with...endwith').
It uses parsing and state-smart objects and classes for resolving
overloading and for early binding: the object or class parses the
selector and determines the method from this.  If the selector is not
parsed by an object or class, it performs a call to the selector for the
active object (late binding), like Zsoter's model.  Fields are always
accessed through the active object.  The big disadvantage of this model
is the parsing and the state-smartness, which reduces extensibility and
increases the opportunities for subtle bugs; essentially, you are only
safe if you never tick or 'postpone' an object or class (Bernd
disagrees, but I (Anton) am not convinced).

   The 'mini-oof.fs' model is quite similar to a very stripped-down
version of the 'objects.fs' model, but syntactically it is a mixture of
the 'objects.fs' and 'oof.fs' models.

   ---------- Footnotes ----------

   (1) A longer version of this critique can be found in 'On
Standardizing Object-Oriented Forth Extensions' (Forth Dimensions, May
1997) by Anton Ertl.

6.25 Regular Expressions
========================

Regular expressions are pattern matching algorithms for strings found in
many contemporary languages.  You can add regular expression
functionality to Gforth with 'require regexp.fs'.

   The classical implementation for this pattern matching is a
backtracking algorithm, which is also necessary if you want to have
features like backreferencing.  Gforth implements regular expressions by
providing a language to define backtracking programs for pattern
matching.  Basic element is the control structure 'FORK' ... 'JOIN',
which is a forward call within a word, and therefore allows to code a
lightweight try and fail control structure.

'FORK' ( compilation -- orig ; run-time f --  ) gforth-0.7 "FORK"
   AHEAD-like control structure: calls the code after JOIN.

'JOIN' ( orig --  ) gforth-0.7 "JOIN"
   THEN-like control structure for FORK

   You can program any sort of arbitrary checks yourself by computing a
flag and '?LEAVE' when the check fails.  Your regular expression code is
enclosed in '((' and '))'.

'((' ( addr u --  ) regexp-pattern "(("
   start regexp block

'))' ( -- flag  ) regexp-pattern "))"
   end regexp block

   Pattern matching in regular expressions have character sets as
elements, so a number of functions allow you to create and modify
character sets (called 'charclass').  All characters here are bytes, so
this doesn't extend to unicode characters.

'charclass' ( --  ) regexp-cg "charclass"
   Create a charclass

'+char' ( char --  ) regexp-cg "+char"
   add a char to the current charclass

'-char' ( char --  ) regexp-cg "-char"
   remove a char from the current charclass

'..char' ( start end --  ) regexp-cg "..char"
   add a range of chars to the current charclass

'+chars' ( addr u --  ) regexp-cg "+chars"
   add a string of chars to the current charclass

'+class' ( class --  ) regexp-cg "+class"
   union of charclass CLASS and the current charclass

'-class' ( class --  ) regexp-cg "-class"
   subtract the charclass CLASS from the current charclass

   There are predefined charclasses and tests for them, and generic
checks.  If a check fails, the next possible alternative of the regular
expression is tried, or a loop is terminated.

'c?' ( addr class --  ) regexp-pattern "c?"
   check ADDR for membership in charclass CLASS

'-c?' ( addr class --  ) regexp-pattern "-c?"
   check ADDR for not membership in charclass CLASS

'\d' ( addr -- addr'  ) regexp-pattern "\d"
   check for digit

'\s' ( addr -- addr'  ) regexp-pattern "\s"
   check for blanks

'.?' ( addr -- addr'  ) regexp-pattern ".?"
   check for any single charachter

'-\d' ( addr -- addr'  ) regexp-pattern "-\d"
   check for not digit

'-\s' ( addr -- addr'  ) regexp-pattern "-\s"
   check for not blank

'`' ( "char" --  ) regexp-pattern "'"
   check for particular char

'`?' ( "char" --  ) regexp-pattern "'?"

'-`' ( "char" --  ) regexp-pattern "-'"
   check for particular char

   You can certainly also check for start and end of the string, and for
whole string constants.

'\^' ( addr -- addr  ) regexp-pattern "\^"
   check for string start

'\$' ( addr -- addr  ) regexp-pattern "\$"
   check for string end

'str=?' ( addr1 addr u -- addr2  ) regexp-pattern "str=?"
   check for a computed string on the stack (possibly a backreference)

   doc-="

   Loops that check for repeated character sets can be greedy or
non-greedy.

'{**' ( addr -- addr addr  ) regexp-pattern "begin-greedy-star"
   greedy zero-or-more pattern

'**}' ( sys --  ) regexp-pattern "end-greedy-star"
   end of greedy zero-or-more pattern

'{++' ( addr -- addr addr  ) regexp-pattern "begin-greedy-plus"
   greedy one-or-more pattern

'++}' ( sys --  ) regexp-pattern "end-greedy-plus"
   end of greedy one-or-more pattern

'{*' ( addr -- addr addr  ) regexp-pattern "begin-non-greedy-star"
   non-greedy zero-or-more pattern

'*}' ( addr addr' -- addr'  ) regexp-pattern "end-non-greedy-star"
   end of non-greedy zero-or-more pattern

'{+' ( addr -- addr addr  ) regexp-pattern "begin-non-greedy-plus"
   non-greedy one-or-more pattern

'+}' ( addr addr' -- addr'  ) regexp-pattern "end-non-greedy-plus"
   end of non-greedy one-or-more pattern

   Example: Searching for a substring really is a non-greedy match of
anything in front of it.

'//' ( --  ) regexp-pattern "//"
   search for string

   Alternatives are written with

'{{' ( addr -- addr addr  ) regexp-pattern "begin-alternatives"
   Start of alternatives

'||' ( addr addr -- addr addr  ) regexp-pattern "next-alternative"
   separator between alternatives

'}}' ( addr addr -- addr  ) regexp-pattern "end-alternatives"
   end of alternatives

   You can use up to 9 variables named '\1' to '\9' to refer to matched
substrings

'\(' ( addr -- addr  ) regexp-pattern "\("
   start of matching variable; variables are referred as \\1--9

'\)' ( addr -- addr  ) regexp-pattern "\)"
   end of matching variable

'\0' ( -- addr u  ) regexp-pattern "\0"
   the whole string

   Certainly, you can also write code to replace patterns you found.

's>>' ( addr -- addr  ) regexp-replace "s>>"
   Start replace pattern region

'>>' ( addr -- addr  ) regexp-replace ">>"
   Start arbitrary replacement code, the code shall compute a string on
the stack and pass it to '<<'

'<<' ( run-addr addr u -- run-addr  ) regexp-replace "<<"
   Replace string from start of replace pattern region with ADDR U

'<<"' ( "string<">" --  ) regexp-replace "<<""
   Replace string from start of replace pattern region with STRING

's//' ( addr u -- ptr  ) regexp-replace "s//"
   start search/replace loop

'//s' ( ptr --  ) regexp-replace "//s"
   search end

'//o' ( ptr addr u -- addr' u'  ) regexp-replace "//o"
   end search/replace single loop

'//g' ( ptr addr u -- addr' u'  ) regexp-replace "//g"
   end search/replace all loop

   Examples can be found in 'test/regexp-test.fs'.

6.26 Programming Tools
======================

6.26.1 Locating source code definitions
---------------------------------------

Many programming systems are organized as an integrated development
environment (IDE) where the editor is the hub of the system, and allows
building and running programs.  If you want that, Gforth has it, too
(*note Emacs and Gforth::).

   However, several Forth systems have a different kind of IDE: The
Forth command line is the hub of the environment; you can view the
source from there in various ways, and call an editor if needed.

   Gforth also implements such an IDE. It mostly follows the conventions
of SwiftForth where they exist, but implements features beyond them.

   An advantage of this approach is that it allows you to use your
favourite editor: set the environment variable 'EDITOR' to your
favourite editor, and the editing commands will call that editor; Gforth
invokes some GUI editors in the background (so you do not need to finish
editing to continue with your Forth session), terminal editors in the
foreground (default for editors not known to Gforth is foreground).  If
you have not set 'EDITOR', the default editor is 'vi'.

'locate' ( "name" --  ) gforth-1.0 "locate"
   Show the source code of the word name and set the current location
there.

   The _current location_ is set by a number of other words in addition
to 'locate'.  Also, when an error happens while loading a file, the
location of the error becomes the current location.

   A number of words work with the current location:

'l' ( --  ) gforth-1.0 "l"
   Display source code lines at the current location.

'n' ( --  ) gforth-1.0 "n"
   Display lines behind the current location, or behind the last 'n' or
'b' output (whichever was later).

'b' ( --  ) gforth-1.0 "b"
   Display lines before the current location, or before the last 'n' or
'b' output (whichever was later).

'g' ( --  ) gforth-0.7 "g"
   Enter the editor at the current location, or at the start of the last
'n' or 'b' output (whichever was later).

   You can control how many lines 'l', 'n' and 'b' show by changing the
values:

'before-locate' ( -- u  ) gforth-1.0 "before-locate"
   number of lines shown before current location (default 3).

'after-locate' ( -- u  ) gforth-1.0 "after-locate"
   number of lines shown after current location (default 12).

   Finally, you can directly go to the source code of a word in the
editor with

'edit' ( "name" --  ) gforth-1.0 "edit"
   Enter the editor at the location of "name"

   You can see the definitions of similarly-named words with

'browse' ( "subname" --  ) gforth-1.0 "browse"
   Show all places where a word with a name that contains subname is
defined ('mwords'-like, *note Word Lists::).  You can then use 'ww',
'nw' or 'bw' (*note Locating uses of a word::) to inspect specific
occurences more closely.

6.26.2 Locating uses of a word
------------------------------

'where' ( "name" --  ) gforth-1.0 "where"
   Show all places where name is used (text-interpreted).  You can then
use 'ww', 'nw' or 'bw' to inspect specific occurences more closely.
Gforth's 'where' does not show the definition of name; use 'locate' for
that.

'ww' ( u --  ) gforth-1.0 "ww"
   The next 'l' or 'g' shows the 'where' result with index u

'nw' ( --  ) gforth-1.0 "nw"
   The next 'l' or 'g' shows the next 'where' result; if the current one
is the last one, after 'nw' there is no current one.  If there is no
current one, after 'nw' the first one is the current one.

'bw' ( --  ) gforth-1.0 "bw"
   The next 'l' or 'g' shows the previous 'where' result; if the current
one is the first one, after 'bw' there is no current one.  If there is
no current one, after 'bw' the last one is the current one.

'gg' ( --  ) gforth-1.0 "gg"
   The next 'ww', 'nw', 'bw', 'bb', 'nb', 'lb' (but not 'locate',
'edit', 'l' or 'g') puts it result in the editor (like 'g').  Use 'gg
gg' to make this permanent rather than one-shot.

'll' ( --  ) gforth-1.0 "ll"
   The next 'ww', 'nw', 'bw', 'bb', 'nb', 'lb' (but not 'locate',
'edit', 'l' or 'g') displays in the Forth system (like 'l').  Use 'll
ll' to make this permanent rather than one-shot.

'whereg' ( "name" --  ) gforth-1.0 "whereg"
   Like 'where', but puts the output in the editor.  In Emacs, you can
then use the compilation-mode commands (*note (emacs)Compilation Mode::)
to inspect specific occurences more closely.

'short-where' ( --  ) gforth-1.0 "short-where"
   Set up 'where' to use a short file format (default).

'expand-where' ( --  ) gforth-1.0 "expand-where"
   Set up 'where' to use a fully expanded file format (to pass to e.g.
editors).

'prepend-where' ( --  ) gforth-1.0 "prepend-where"
   Set up 'where' to show the file on a separate line, followed by
'where' lines without file names (like SwiftForth).

   The data we have on word usage also allows us to show which words
have no uses:

'unused-words' ( --  ) gforth-1.0 "unused-words"
   list all words without usage

6.26.3 Locating exception source
--------------------------------

'tt' ( u --  ) gforth-1.0 "tt"

'nt' (  --  ) gforth-1.0 "nt"

'bt' ( --  ) gforth-1.0 "bt"

6.26.4 Examining compiled code
------------------------------

And finally, 'see' and friends show compiled code.  Some of the things
in the source code are not present in the compiled code (e.g.,
formatting and comments), but this is useful to see what threaded code
or native code is produced by macros and Gforth's optimization features.

'see' ( "<spaces>name" --  ) tools "see"
   Locate NAME using the current search order.  Display the definition
of NAME.  Since this is achieved by decompiling the definition, the
formatting is mechanised and some source information (comments,
interpreted sequences within definitions etc.)  is lost.

'xt-see' ( xt --  ) gforth-0.2 "xt-see"
   Decompile the definition represented by xt.

'simple-see' ( "name" --  ) gforth-0.6 "simple-see"
   Decompile the colon definition name, showing a line for each cell,
and try to guess a meaning for the cell, and show that.

'xt-simple-see' ( xt --  ) gforth-1.0 "xt-simple-see"
   Decompile the colon definition xt like 'simple-see'

'simple-see-range' ( addr1 addr2 --  ) gforth-0.6 "simple-see-range"
   Decompile code in [addr1,addr2) like 'simple-see'

'see-code' ( "name" --  ) gforth-0.7 "see-code"
   Like 'simple-see', but also shows the dynamic native code for the
inlined primitives.  For static superinstructions, it shows the
primitive sequence instead of the first primitive (the other primitives
of the superinstruction are shown, too).  For primitives for which
native code is generated, it shows the number of stack items in
registers at the beginning and at the end (e.g., '1->1' means 1 stack
item is in a register at the start and at the end).  For each primitive
or superinstruction with native code, the inline arguments and component
primitives are shown first, then the native code.

'xt-see-code' ( xt --  ) gforth-1.0 "xt-see-code"
   Decompile the colon definition xt like 'see-code'.

'see-code-range' ( addr1 addr2 --  ) gforth-0.7 "see-code-range"
   Decompile code in [addr1,addr2) like 'see-code'.

   As an example, consider:

     : foo x f@ fsin drop over ;

   This is not particularly useful, but it demonstrates the various code
generation differences.  Compiling this on 'gforth-fast' on AMD64 and
then using 'see-code foo' outputs:

     $7FD0CEE8C510 lit f@     1->1
     $7FD0CEE8C518 x
     $7FD0CEE8C520 f@
     7FD0CEB51697:   movsd   [r12],xmm15
     7FD0CEB5169D:   mov     rax,$00[r13]
     7FD0CEB516A1:   sub     r12,$08
     7FD0CEB516A5:   add     r13,$18
     7FD0CEB516A9:   movsd   xmm15,[rax]
     7FD0CEB516AE:   mov     rcx,-$08[r13]
     7FD0CEB516B2:   jmp     ecx
     $7FD0CEE8C528 fsin
     $7FD0CEE8C530 drop    1->0
     7FD0CEB516B4:   add     r13,$08
     $7FD0CEE8C538 over    0->1
     7FD0CEB516B8:   mov     r8,$10[r15]
     7FD0CEB516BC:   add     r13,$08
     $7FD0CEE8C540 ;s    1->1
     7FD0CEB516C0:   mov     r10,[rbx]
     7FD0CEB516C3:   add     rbx,$08
     7FD0CEB516C7:   lea     r13,$08[r10]
     7FD0CEB516CB:   mov     rcx,-$08[r13]
     7FD0CEB516CF:   jmp     ecx

   First, you see a threaded-code cell for a static superinstruction
with the components 'lit' and 'f@', starting and ending with one data
stack item in a register ('1->1'); this is followed by the cell for the
argument 'x' of 'lit', and the cell for the 'f@' component of the
superinstruction; the latter cell is not used, but is there for
Gforth-internal reasons.

   Next, the dynamically generated native code for the superinstruction
'lit f@' is shown; note that this native code is not mixed with the
threaded code in memory, as you can see by comparing the addresses.

   If you want to understand the native code shown here: the
threaded-code instruction pointer is in 'r13', the data stack pointer in
'r15'; the first data stack register is 'r8' (i.e., the top of stack
resides there if there is one data stack item in a register); the return
stack pointer is in 'rbx', the FP stack pointer in 'r12', and the top of
the floating-pont stack in 'xmm15'.  Note that the register assignments
vary between engines, so you may see a different register assignment for
this code.

   The dynamic native code for 'lit f@' ends with a dispatch jump (aka
NEXT), because the code for the next word 'fsin' in the definition is
not dynamically generated.

   Next, you see the threaded-code cell for 'fsin'.  There is no
dynamically-generated native code for this word, and 'see-code' does not
show the static native code for it (you can look at it with 'see fsin').
Like all words with static native code in 'gforth-fast', the effect on
the data stack representation is '1->1' (for 'gforth', '0->0'), but this
is not shown.

   Next, you see the threaded-code cell for 'drop'; the native-code
variant used here starts with one data stack item in registers, and ends
with zero data stack items in registers ('1->0').  This is followed by
the native code for this variant of 'drop'.  There is no NEXT here,
because the native code falls through to the code for the next word.

   Next, you see the threaded-code cell for 'over' followed by the
dynamically-generated native code in the '0->1' variant.

   Finally, you see the threaded and native code for ';s' (the primitive
compiled for ';' in 'foo').  ';s' performs control flow (it returns), so
it has to end with a NEXT.

6.26.5 Examining data and code
------------------------------

The following words inspect the stack non-destructively:

'...' ( x1 .. xn -- x1 .. xn  ) gforth-1.0 "..."
   smart version of '.s'

'.s' ( --  ) tools "dot-s"
   Display the number of items on the data stack, followed by a list of
the items (but not more than specified by 'maxdepth-.s'; TOS is the
right-most item.

'f.s' ( --  ) gforth-0.2 "f-dot-s"
   Display the number of items on the floating-point stack, followed by
a list of the items (but not more than specified by 'maxdepth-.s'; TOS
is the right-most item.

'f.s-precision' ( -- u  ) gforth-1.0 "f.s-precision"
   A 'value'.  U is the field width for f.s output.  Other precision
details are derived from that value.

'maxdepth-.s' ( -- addr  ) gforth-0.2 "maxdepth-dot-s"
   A variable containing 9 by default.  '.s' and 'f.s' display at most
that many stack items.

   There is a word '.r' but it does not display the return stack!  It is
used for formatted numeric output (*note Simple numeric output::).

   The following words work on the stack as a whole, either by
determining the depth or by clearing them:

'depth' ( -- +n  ) core "depth"
   +N is the number of values that were on the data stack before +N
itself was placed on the stack.

'fdepth' ( -- +n  ) floating "f-depth"
   +n is the current number of (floating-point) values on the
floating-point stack.

'clearstack' ( ... --  ) gforth-0.2 "clear-stack"
   remove and discard all/any items from the data stack.

'fclearstack' ( r0 .. rn --  ) gforth-1.0 "f-clearstack"
   clear the floating point stack

'clearstacks' ( ... --  ) gforth-0.7 "clear-stacks"
   empty data and FP stack

   The following words inspect memory.

'?' ( a-addr --  ) tools "question"
   Display the contents of address A-ADDR in the current number base.

'dump' ( addr u --  ) tools "dump"
   Display U lines of memory starting at address ADDR.  Each line
displays the contents of 16 bytes.  When Gforth is running under an
operating system you may get 'Invalid memory address' errors if you
attempt to access arbitrary locations.

6.26.6 Forgetting words
-----------------------

Forth allows you to forget words (and everything that was alloted in the
dictonary after them) in a LIFO manner.

'marker' ( "<spaces> name" --  ) core-ext "marker"
   Create a definition, name (called a mark) whose execution semantics
are to remove itself and everything defined after it.

   The most common use of this feature is during progam development:
when you change a source file, forget all the words it defined and load
it again (since you also forget everything defined after the source file
was loaded, you have to reload that, too).  Note that effects like
storing to variables and destroyed system words are not undone when you
forget words.  With a system like Gforth, that is fast enough at
starting up and compiling, I find it more convenient to exit and restart
Gforth, as this gives me a clean slate.

   Here's an example of using 'marker' at the start of a source file
that you are debugging; it ensures that you only ever have one copy of
the file's definitions compiled at any time:

     [IFDEF] my-code
         my-code
     [ENDIF]

     marker my-code
     init-included-files

     \ .. definitions start here
     \ .
     \ .
     \ end

6.26.7 Debugging
----------------

Languages with a slow edit/compile/link/test development loop tend to
require sophisticated tracing/stepping debuggers to facilate debugging.

   A much better (faster) way in fast-compiling languages is to add
printing code at well-selected places, let the program run, look at the
output, see where things went wrong, add more printing code, etc., until
the bug is found.

   The simple debugging aids provided in 'debugs.fs' are meant to
support this style of debugging.

   The word '~~' prints debugging information (by default the source
location and the stack contents).  It is easy to insert.  If you use
Emacs it is also easy to remove ('C-x ~' in the Emacs Forth mode to
query-replace them with nothing).  The deferred words 'printdebugdata'
and '.debugline' control the output of '~~'.  The default source
location output format works well with Emacs' compilation mode, so you
can step through the program at the source level using 'C-x `' (the
advantage over a stepping debugger is that you can step in any direction
and you know where the crash has happened or where the strange data has
occurred).

'~~' ( --  ) gforth-0.2 "tilde-tilde"
   Prints the source code location of the '~~' and the stack contents
with '.debugline'.

'printdebugdata' ( --  ) gforth-0.2 "print-debug-data"

'.debugline' ( nfile nline --  ) gforth-0.6 "print-debug-line"
   Print the source code location indicated by NFILE NLINE, and
additional debugging information; the default '.debugline' prints the
additional information with 'printdebugdata'.

'debug-fid' ( -- file-id  ) gforth-1.0 "File-id"
   debugging words for output.  By default it is the process's 'stderr'.

   '~~' (and assertions) will usually print the wrong file name if a
marker is executed in the same file after their occurance.  They will
print '*somewhere*' as file name if a marker is executed in the same
file before their occurance.

'once' ( --  ) gforth-1.0 "once"
   do the following up to THEN only once

'~~bt' ( --  ) gforth-1.0 "~~bt"
   print stackdump and backtrace

'~~1bt' ( --  ) gforth-1.0 "~~1bt"
   print stackdump and backtrace once

'???' ( --  ) gforth-0.2 "???"
   Open a debuging shell

'WTF??' ( --  ) gforth-1.0 "WTF??"
   Open a debugging shell with backtrace and stack dump

'!!FIXME!!' ( --  ) gforth-1.0 "!!FIXME!!"
   word that should never be reached

'replace-word' ( xt1 xt2 --  ) gforth-1.0 "replace-word"
   make xt2 do xt1, both need to be colon definitions

'~~Variable' ( "name" --  ) gforth-1.0 "~~Variable"
   Variable that will be watched on every access

'~~Value' ( n "name" --  ) gforth-1.0 "~~Value"
   Value that will be watched on every access

'+ltrace' ( --  ) gforth-1.0 "+ltrace"
   turn on line tracing

'-ltrace' ( --  ) gforth-1.0 "-ltrace"
   turn off line tracing

'#loc' ( nline nchar "file" --  ) gforth-1.0 "#loc"
   set next word's location to NLINE NCHAR in "FILE"

6.26.8 Assertions
-----------------

It is a good idea to make your programs self-checking, especially if you
make an assumption that may become invalid during maintenance (for
example, that a certain field of a data structure is never zero).
Gforth supports "assertions" for this purpose.  They are used like this:

     assert( flag )

   The code between 'assert(' and ')' should compute a flag, that should
be true if everything is alright and false otherwise.  It should not
change anything else on the stack.  The overall stack effect of the
assertion is '( -- )'.  E.g.

     assert( 1 1 + 2 = ) \ what we learn in school
     assert( dup 0<> ) \ assert that the top of stack is not zero
     assert( false ) \ this code should not be reached

   The need for assertions is different at different times.  During
debugging, we want more checking, in production we sometimes care more
for speed.  Therefore, assertions can be turned off, i.e., the assertion
becomes a comment.  Depending on the importance of an assertion and the
time it takes to check it, you may want to turn off some assertions and
keep others turned on.  Gforth provides several levels of assertions for
this purpose:

'assert0(' ( --  ) gforth-0.2 "assert-zero"
   Important assertions that should always be turned on.

'assert1(' ( --  ) gforth-0.2 "assert-one"
   Normal assertions; turned on by default.

'assert2(' ( --  ) gforth-0.2 "assert-two"
   Debugging assertions.

'assert3(' ( --  ) gforth-0.2 "assert-three"
   Slow assertions that you may not want to turn on in normal debugging;
you would turn them on mainly for thorough checking.

'assert(' ( --  ) gforth-0.2 "assert("
   Equivalent to 'assert1('

')' ( --  ) gforth-0.2 "close-paren"
   End an assertion.  Generic end, can be used for other similar
purposes

   The variable 'assert-level' specifies the highest assertions that are
turned on.  I.e., at the default 'assert-level' of one, 'assert0(' and
'assert1(' assertions perform checking, while 'assert2(' and 'assert3('
assertions are treated as comments.

   The value of 'assert-level' is evaluated at compile-time, not at
run-time.  Therefore you cannot turn assertions on or off at run-time;
you have to set the 'assert-level' appropriately before compiling a
piece of code.  You can compile different pieces of code at different
'assert-level's (e.g., a trusted library at level 1 and newly-written
code at level 3).

'assert-level' ( -- a-addr  ) gforth-0.2 "assert-level"
   All assertions above this level are turned off.

   If an assertion fails, a message compatible with Emacs' compilation
mode is produced and the execution is aborted (currently with 'ABORT"'.
If there is interest, we will introduce a special throw code.  But if
you intend to 'catch' a specific condition, using 'throw' is probably
more appropriate than an assertion).

   Assertions (and '~~') will usually print the wrong file name if a
marker is executed in the same file after their occurance.  They will
print '*somewhere*' as file name if a marker is executed in the same
file before their occurance.

   Definitions in Standard Forth for these assertion words are provided
in 'compat/assert.fs'.

6.26.9 Singlestep Debugger
--------------------------

The singlestep debugger works only with the engine 'gforth-itc'.

   When you create a new word there's often the need to check whether it
behaves correctly or not.  You can do this by typing 'dbg badword'.  A
debug session might look like this:

     : badword 0 DO i . LOOP ;  ok
     2 dbg badword
     : badword
     Scanning code...

     Nesting debugger ready!

     400D4738  8049BC4 0              -> [ 2 ] 00002 00000
     400D4740  8049F68 DO             -> [ 0 ]
     400D4744  804A0C8 i              -> [ 1 ] 00000
     400D4748 400C5E60 .              -> 0 [ 0 ]
     400D474C  8049D0C LOOP           -> [ 0 ]
     400D4744  804A0C8 i              -> [ 1 ] 00001
     400D4748 400C5E60 .              -> 1 [ 0 ]
     400D474C  8049D0C LOOP           -> [ 0 ]
     400D4758  804B384 ;              ->  ok

   Each line displayed is one step.  You always have to hit return to
execute the next word that is displayed.  If you don't want to execute
the next word in a whole, you have to type 'n' for 'nest'.  Here is an
overview what keys are available:

<RET>
     Next; Execute the next word.

n
     Nest; Single step through next word.

u
     Unnest; Stop debugging and execute rest of word.  If we got to this
     word with nest, continue debugging with the calling word.

d
     Done; Stop debugging and execute rest.

s
     Stop; Abort immediately.

   Debugging large application with this mechanism is very difficult,
because you have to nest very deeply into the program before the
interesting part begins.  This takes a lot of time.

   To do it more directly put a 'BREAK:' command into your source code.
When program execution reaches 'BREAK:' the single step debugger is
invoked and you have all the features described above.

   If you have more than one part to debug it is useful to know where
the program has stopped at the moment.  You can do this by the 'BREAK"
string"' command.  This behaves like 'BREAK:' except that string is
typed out when the "breakpoint" is reached.

'dbg' ( "name" --  ) gforth-0.2 "dbg"

'break:' ( --  ) gforth-0.4 "break:"

'break"' ( 'ccc"' --  ) gforth-0.4 "break""

6.26.10 Code Coverage and Execution Frequency
---------------------------------------------

If you run extensive tests on your code, you often want to figure out if
the tests exercise all parts of the code.  This is called (test)
coverage.  The file 'coverage.fs' contains tools for measuring the
coverage as well as execution frequency.

   Code coverage inserts counting code in every basic block
(straight-line code sequence) loaded after 'coverage.fs'.  Each time
that code is run, it increments the counter for that basic block.  Later
you can show the source file with the counts inserted in these basic
blocks.

'nocov[' ( --  ) gforth-1.0 "nocov-bracket"
   (Immediate) Turn coverage off temporarily.

']nocov' ( --  ) gforth-1.0 "bracket-nocov"
   (Immediate) End of temporary turned off coverage.

'coverage?' ( -- f  ) gforth-internal "coverage?"
   Value: Coverage check on/off

'cov+' ( --  ) gforth-experimental "cov+"
   (Immediate) Place a coverage counter here.

'?cov+' ( flag -- flag  ) gforth-experimental "?cov+"
   (Immediate) A coverage counter for a flag; in the coverage output you
see three numbers behind '?cov': The first is the number of executions
where the top-of-stack was non-zero; the second is the number of
executions where it was zero; the third is the total number of
executions.

'.coverage' ( --  ) gforth-experimental ".coverage"
   Show code with execution frequencies.

'annotate-cov' ( --  ) gforth-experimental "annotate-cov"
   For every file with coverage information, produce a '.cov' file that
has the execution frequencies inserted.  We recommend to use 'bw-cover'
first (with the default 'color-cover' you get escape sequences in the
files).

'cov%' ( --  ) gforth-experimental "cov-percent"
   Print the percentage of basic blocks loaded after 'coverage.fs' that
are executed at least once.

'.cover-raw' ( --  ) gforth-experimental ".cover-raw"
   Print raw execution counts.

   By default, the counts are shown in colour (using ANSI escape
sequences), but you can use 'bw-cover' to show them in parenthesized
form without escape sequences.

'bw-cover' ( --  ) gforth-1.0 "bw-cover"
   Print execution counts in parentheses (source-code compatible).

'color-cover' ( --  ) gforth-1.0 "color-cover"
   Print execution counts in colours (default).

   You can save and reload the coverage counters in binary format, to
aggregate coverage counters across several test runs.

'save-cov' ( --  ) gforth-experimental "save-cov"
   Save coverage counters.

'load-cov' ( --  ) gforth-experimental "load-cov"
   Load coverage counters.

6.27 Multitasker
================

Gforth offers two multitaskers: a traditional, cooperative round-robin
multitasker, and a pthread-based multitasker which allows to run several
threads concurrently on multi-core machines.  The pthread-based is now
marked as experimental feature, as standardization of Forth multitaskers
will likely change the names of words without changing their semantics.

6.27.1 Pthreads
---------------

Posix threads can run in parallel on several cores, or with pre-emptive
multitasking on onecore.  However, many of the following words are the
same as in the traditional cooperative multi-tasker.

   In addition, there are words that allow you to make sure that only
one task at a time changes something, and for communicating between
tasks.  These words are necessary for pre-emptive and multi-core
multi-tasking, because the cooperative-multitasking way of performing
transactions between calls to 'pause' does not work in this environment.

6.27.1.1 Basic multi-tasking
............................

Tasks can be created with 'newtask' or 'newtask4' with a given amount of
stack space (either all the same or each stack's size specified).

'newtask' ( stacksize -- task  ) gforth-experimental "newtask"
   creates task; each stack (data, return, FP, locals) has size
stacksize.

'task' ( ustacksize "name" --  ) gforth-experimental "task"
   creates a task name; each stack (data, return, FP, locals) has size
ustacksize.
name execution: ( -- task )

'newtask4' ( u-data u-return u-fp u-locals -- task  ) gforth-experimental "newtask4"
   creates task with data stack size u-data, return stack size u-return,
FP stack size u-fp and locals stack size u-locals.

   If you don't know which stack sizes to use for the task, you can use
the size(s) of the main task:

'stacksize' ( -- u  ) gforth-experimental "stacksize"
   u is the data stack size of the main task.

'stacksize4' ( -- u-data u-return u-fp u-locals  ) gforth-experimental "stacksize4"
   Pushes the data, return, FP, and locals stack sizes of the main task.

   A task is created in an inactive state.  To let it run, you have to
activate it with one of the following words:

'initiate' ( xt task --  ) gforth-experimental "initiate"
   Let task execute xt.  Upon return from the xt, the task terminates
itself (VFX compatible).  Use one-time executable closures to pass
arbitrary paramenters to a task.

   The following legacy words provide the same functionality as
'initiate', but with a different interface: Like 'does>', they split
their containing colon definition in two parts: The part before
'activate'/'pass' runs in the activating task, and returns to its caller
after activating the task.  The part behind 'activate'/'pass' is
executed in the activated target task.

'activate' ( run-time nest-sys1 task --  ) gforth-experimental "activate"
   Let task perform the code behind 'activate', and return to the caller
of the word containing 'activate'.  When the task returns from the code
behind 'activate', it terminates itself.

'pass' ( x1 .. xn n task --  ) gforth-experimental "pass"
   Pull x1 ..  xn n from the current task's data stack and push x1 ..
xn on task's data stack.  Let task perform the code behind 'pass', and
return to the caller of the word containing 'pass'.  When the task
returns from the code behind 'pass', it terminates itself.

   You can also do creation and activation in one step:

'execute-task' ( xt -- task  ) gforth-experimental "execute-task"
   Create a new task TASK with the same stack sizes as the main task.
Let task execute xt.  Upon return from the xt, the task terminates
itself.

   Apart from terminating by running to the end, a task can terminate
itself with 'kill-task'.  Other tasks can terminate it with 'kill'.

'kill-task' ( --  ) gforth-experimental "kill-task"
   Terminate the current task.

'kill' ( task --  ) gforth-experimental "kill"
   Terminate task.

   Tasks can also temporarily stop themselves or be stopped:

'halt' ( task --  ) gforth-experimental "halt"
   Stop a task

'stop' ( --  ) gforth-experimental "stop"
   stops the current task, and waits for events (which may restart it)

'stop-ns' ( timeout --  ) gforth-experimental "stop-ns"
   Stop with timeout (in nanoseconds), better replacement for ms

   A task restarts when the timeout is over or when another task wakes
it with:

'restart' ( task --  ) gforth-experimental "restart"
   Wake a task

   There is also:

'pause' ( --  ) gforth-experimental "pause"
   voluntarily switch to the next waiting task ('pause' is the
traditional cooperative task switcher; in the pthread multitasker, you
don't need 'pause' for cooperation, but you still can use it e.g.  when
you have to resort to polling for some reason).  This also checks for
events in the queue.

6.27.1.2 Task-local data
........................

In Forth every task has essentially the same task-local data, called
"user" area (early Forth systems were multi-user systems and there often
was one user per task).  The task result of, e.g.  'newtask' is the
start address of its user area.  Each task gets the user data defined by
the system (e.g., 'base').  You can define additional user data with:

'User' ( "name" --  ) gforth-0.2 "User"
   Name is a user variable (1 cell).
Name execution: ( -- addr )
Addr is the address of the user variable in the current task.

'AUser' ( "name" --  ) gforth-0.2 "AUser"
   Name is a user variable containing an address (this only makes a
difference in the cross-compiler).

'uallot' ( n1 -- n2  ) gforth-0.3 "uallot"
   Reserve n1 bytes of user data.  n2 is the offset of the start of the
reserved area within the user area.

'UValue' ( "name" --  ) gforth-1.0 "UValue"
   Name is a user value.
Name execution: ( -- x )

'UDefer' ( "name" --  ) gforth-1.0 "UDefer"
   Name is a task-local deferred word.
Name execution: ( ...  -- ...  )

   There are also the following words for dealing with user data.

'up@' ( -- a-addr ) new "up-fetch"
   Addr is the start of the user area of the current task (addr also
serves as the task identifier of the current task).

'user'' ( "name" -- u  ) gforth-experimental "user"'
   U is the offset of the user variable name in the user area of each
task.

''s' ( addr1 task -- addr2  ) gforth-experimental "'s"
   With addr1 being an address in the user data of the current task,
addr2 is the corresponding address in task's user data.

6.27.1.3 Semaphores
...................

A cooperative multitasker can ensure that there is no other task
interacting between two invocations of 'pause'.  Pthreads however are
really concurrent tasks (at least on a multi-core CPU), and therefore,
several techniques to avoid conflicts when accessing the same resources.

   Semaphores can only be aquired by one thread, all other threads have
to wait until the semapohre is released.

'semaphore' ( "name" --  ) gforth-experimental "semaphore"
   create a named semaphore name
name execution: ( -- semaphore )

'lock' ( semaphore --  ) gforth-experimental "lock"
   lock the semaphore

'unlock' ( semaphore --  ) gforth-experimental "unlock"
   unlock the semaphore

   The other approach to prevent concurrent access is the critical
section.  Here, we implement a critical section with a semaphore, so you
have to specify the semaphore which is used for the critical section.
Only those critical sections which use the same semaphore are mutually
exclusive.

'critical-section' ( xt semaphore --  ) gforth-experimental "critical-section"
   Execute xt while locking semaphore.  After leaving xt, semaphore is
unlocked even if an exception is thrown.

6.27.1.4 Hardware operations for multi-tasking
..............................................

Atomic hardware operations perform the whole operation, without any
other task seeing an intermediate state.  These operations can be used
to synchronize tasks without using slow OS primitives, but compared to
the non-atomic sequences of operations they tend to be slow.  Atomic
operations only work correctly on aligned addresses, even on hardware
that otherwise does not require alignment.

'!@' ( u1 a-addr -- u2 ) gforth-experimental "store-fetch"
   load U2 from A_ADDR, and store U1 there, as atomic operation

'+!@' ( u1 a-addr -- u2 ) gforth-experimental "add-store-fetch"
   load U2 from A_ADDR, and increment this location by U1, as atomic
operation

'?!@' ( unew uold a-addr -- uprev ) gforth-experimental "question-store-fetch"
   load UPREV from A_ADDR, compare it to UOLD, and if equal, store UNEW
there, as atomic operation

   Another hardware operation is the memory barrier.  Unfortunately
modern hardware often can reorder memory operations relative to other
memory operations (as seen by a different core), and the memory barrier
suppresses this reordering for one point in the execution of the task.

'barrier' ( -- ) gforth-experimental "barrier"
   All memory operations before the barrier are performed before any
memory operation after the barrier.

6.27.1.5 Message queues
.......................

Gforth's message queues are a variant of the actor model.

   An event is an xt; the sending task tells the receiving task to run
an event, and the receiving task performs one event from its message
queue when it is ready.  Execute-once closures can be used for events
that pass parameters.

'send-event' ( xt task --  ) gforth-experimental "send-event"
   Task IPC: send XT to TASK.  The xt is executed there.  Use a one-shot
closure to pass parameters with the xt.

   When several tasks send event to one task, the events may arrive in
any order.  In order to receive events, you put one of the following
words in the receiving task:

'?events' ( --  ) gforth-experimental "question-events"
   Perform all event sequences in the current task's message queue, one
event sequence at a time.

'event-loop' ( --  ) gforth-experimental "event-loop"
   Wait for event sequences, and execute any event sequences when they
arrive.  Return to waiting if no event sequences are in the queue.  This
word never returns.

   Alternatively, when a task is 'stop'ped, it is also ready for
receiving event, and receiving an event will wake it up.

6.27.2 Cilk
-----------

Gforth's Cilk is a framework for dividing work between multiple tasks
running on several cores, inspired by the programming language of the
same name.  Use 'require cilk.fs' if you want to use Cilk.

   The idea is that you identify subproblems that can be solved in
parallel, and the framework assigns worker tasks to these subproblems.
In particular, you use one of the 'spawn' words for each subtask.
Eventually you need to wait with 'cilk-sync' for the subproblems to be
solved.

   Currently all the spawning has to happen from one task, and
'cilk-sync' waits for all subproblems to complete, so using the current
Gforth Cilk for recursive algorithms is not straightforward.

   Do not divide the subproblems too finely, in order to avoid overhead;
how fine is too fine depends on how uniform the run-time for the
subproblems is, but for problems with substantial run-time, having
5*'cores' subproblems is probably a good starting point.

'cores' ( -- u  ) cilk "cores"
   A value containing the number of worker tasks to use.  By default
this is the number of hardware threads (with SMT/HT), if we can
determine that, otherwise 1.  If you want to use a different number,
change 'cores' before calling 'cilk-init'.

'cilk-init' ( --  ) cilk "cilk-init"
   Start the worker tasks if not already done.

'spawn' ( xt --  ) cilk "spawn"
   Execute xt ( -- ) in a worker task.  Use one-time executable closures
to pass heap-allocated closures, allowing to pass arbitrary data from
the spawner to the code running in the worker.
E.g.: '( n r ) [{: n f: r :}h1 code ;] spawn'

'spawn1' ( x xt --  ) cilk "spawn1"
   Execute xt ( x -- ) in a worker task.

'spawn2' ( x1 x2 xt --  ) cilk "spawn2"
   Execute xt ( x1 x2 -- ) in a worker task.

'cilk-sync' ( --  ) cilk "cilk-sync"
   Wait for all subproblems to complete.

'cilk-bye' ( --  ) cilk "cilk-bye"
   Terminate all workers.

6.28 C Interface
================

Gforth's C interface works by compiling a wrapper library that contains
C functions which take parameters from the Forth stacks and calls the C
functions.  This wrapper library is compiled by the C compiler.
Compilation results are cached, so that Gforth only needs to rerun the C
compilation if the wrapper library has to change.  This build process is
automatic, and done at the end of a interface declaration.  Gforth uses
libtool and GCC for that process.

   The C interface is now mostly complete, callbacks have been added,
but for structs, we use Forth2012 structs, which don't have independent
scopes.  The offsets of those structs are extracted from header files
with a SWIG plugin.

6.28.1 Calling C functions
--------------------------

Once a C function is declared (see *note Declaring C Functions::), you
can call it as follows: You push the arguments on the stack(s), and then
call the word for the C function.  The arguments have to be pushed in
the same order as the arguments appear in the C documentation (i.e., the
first argument is deepest on the stack).  Integer and pointer arguments
have to be pushed on the data stack, floating-point arguments on the FP
stack; these arguments are consumed by the called C function.

   On returning from the C function, the return value, if any, resides
on the appropriate stack: an integer return value is pushed on the data
stack, an FP return value on the FP stack, and a void return value
results in not pushing anything.  Note that most C functions have a
return value, even if that is often not used in C; in Forth, you have to
'drop' this return value explicitly if you do not use it.

   The C interface automatically converts between the C type and the
Forth type as necessary, on a best-effort basis (in some cases, there
may be some loss).

   As an example, consider the POSIX function 'lseek()':

     off_t lseek(int fd, off_t offset, int whence);

   This function takes three integer arguments, and returns an integer
argument, so a Forth call for setting the current file offset to the
start of the file could look like this:

     fd @ 0 SEEK_SET lseek -1 = if
       ... \ error handling
     then

   You might be worried that an 'off_t' does not fit into a cell, so you
could not pass larger offsets to lseek, and might get only a part of the
return values.  In that case, in your declaration of the function (*note
Declaring C Functions::) you should declare it to use double-cells for
the off_t argument and return value, and maybe give the resulting Forth
word a different name, like 'dlseek'; the result could be called like
this:

     fd @ 0. SEEK_SET dlseek -1. d= if
       ... \ error handling
     then

   Passing and returning structs or unions is currently not supported by
our interface(1).

   Calling functions with a variable number of arguments (_variadic_
functions, e.g., 'printf()') is only supported by having you declare one
function-calling word for each argument pattern, and calling the
appropriate word for the desired pattern.

   ---------- Footnotes ----------

   (1) If you know the calling convention of your C compiler, you
usually can call such functions in some way, but that way is usually not
portable between platforms, and sometimes not even between C compilers.

6.28.2 Declaring C Functions
----------------------------

Before you can call 'lseek' or 'dlseek', you have to declare it.  The
declaration consists of two parts:

The C part
     is the C declaration of the function, or more typically and
     portably, a C-style '#include' of a file that contains the
     declaration of the C function.

The Forth part
     declares the Forth types of the parameters and the Forth word name
     corresponding to the C function.

   For the words 'lseek' and 'dlseek' mentioned earlier, the
declarations are:

     \c #define _FILE_OFFSET_BITS 64
     \c #include <sys/types.h>
     \c #include <unistd.h>
     c-function lseek lseek n n n -- n
     c-function dlseek lseek n d n -- d

   The C part of the declarations is prefixed by '\c', and the rest of
the line is ordinary C code.  You can use as many lines of C
declarations as you like, and they are visible for all further function
declarations.

   The Forth part declares each interface word with 'c-function',
followed by the Forth name of the word, the C name of the called
function, and the stack effect of the word.  The stack effect contains
an arbitrary number of types of parameters, then '--', and then exactly
one type for the return value.  The possible types are:

'n'
     single-cell integer

'a'
     address (single-cell)

'd'
     double-cell integer

'r'
     floating-point value

'func'
     C function pointer

'void'
     no value (used as return type for void functions)

   To deal with variadic C functions, you can declare one Forth word for
every pattern you want to use, e.g.:

     \c #include <stdio.h>
     c-function printf-nr printf a n r -- n
     c-function printf-rn printf a r n -- n

   Note that with C functions declared as variadic (or if you don't
provide a prototype), the C interface has no C type to convert to, so no
automatic conversion happens, which may lead to portability problems in
some cases.  You can add the C type cast in curly braces after the Forth
type.  This also allows to pass e.g.  structs to C functions, which in
Forth cannot live on the stack.

     c-function printfll printf a n{(long long)} -- n
     c-function pass-struct pass_struct a{*(struct foo *)} -- n

   This typecasting is not available to return values, as C does not
allow typecasts for lvalues.

'\c' ( "rest-of-line" --  ) gforth-0.7 "backslash-c"
   One line of C declarations for the C interface

'c-function' ( "forth-name" "c-name" "{type}" "---" "type" --  ) gforth-0.7 "c-function"
   Define a Forth word forth-name.  Forth-name has the specified stack
effect and calls the C function 'c-name'.

'c-value' ( "forth-name" "c-name" "---" "type" --  ) gforth-1.0 "c-value"
   Define a Forth word forth-name.  Forth-name has the specified stack
effect and gives the C value of 'c-name'.

'c-variable' ( "forth-name" "c-name" --  ) gforth-1.0 "c-variable"
   Define a Forth word forth-name.  Forth-name returns the address of
'c-name'.

   In order to work, this C interface invokes GCC at run-time and uses
dynamic linking.  If these features are not available, there are other,
less convenient and less portable C interfaces in 'lib.fs' and
'oldlib.fs'.  These interfaces are mostly undocumented and mostly
incompatible with each other and with the documented C interface; you
can find some examples for the 'lib.fs' interface in 'lib.fs'.

6.28.3 Calling C function pointers from Forth
---------------------------------------------

If you come across a C function pointer (e.g., in some C-constructed
structure) and want to call it from your Forth program, you could use
the structures as described above by defining a macro.  Or you use
'c-funptr'.

'c-funptr' ( "forth-name" <{>"c-typecast"<}> "{type}" "---" "type" --  ) gforth-1.0 "c-funptr"
   Define a Forth word forth-name.  Forth-name has the specified stack
effect plus the called pointer on top of stack, i.e.  '( {type} ptr --
type )' and calls the C function pointer 'ptr' using the typecast or
struct access 'c-typecast'.

   Let us assume that there is a C function pointer type 'func1' defined
in some header file 'func1.h', and you know that these functions take
one integer argument and return an integer result; and you want to call
functions through such pointers.  Just define

     \c #include <func1.h>
     c-funptr call-func1 {((func1)ptr)} n -- n

   and then you can call a function pointed to by, say 'func1a' as
follows:

     -5 func1a call-func1 .

   The Forth word 'call-func1' is similar to 'execute', except that it
takes a C 'func1' pointer instead of a Forth execution token, and it is
specific to 'func1' pointers.  For each type of function pointer you
want to call from Forth, you have to define a separate calling word.

6.28.4 Defining library interfaces
----------------------------------

You can give a name to a bunch of C function declarations (a library
interface), as follows:

     c-library lseek-lib
     \c #define _FILE_OFFSET_BITS 64
     ...
     end-c-library

   The effect of giving such a name to the interface is that the names
of the generated files will contain that name, and when you use the
interface a second time, it will use the existing files instead of
generating and compiling them again, saving you time.  The generated
file contains a 128 bit hash (not cryptographically safe, but good
enough for that purpose) of the source code, so changing the
declarations will cause a new compilation.  Normally these files are
cached in '$HOME/.gforth/'ARCHITECTURE'/libcc-named', so if you
experience problems or have other reasons to force a recompilation, you
can delete the files there.

   Note that you should use 'c-library' before everything else having
anything to do with that library, as it resets some setup stuff.  The
idea is that the typical use is to put each
'c-library'...'end-c-library' unit in its own file, and to be able to
include these files in any order.  All other words dealing with the C
interface are hidden in the vocabulary 'c-lib', which is put on top o
the search stack by 'c-library' and removed by 'end-c-library'.

   Note that the library name is not allocated in the dictionary and
therefore does not shadow dictionary names.  It is used in the file
system, so you have to use naming conventions appropriate for file
systems.  The name is also used as part of the C symbols, but characters
outside the legal C symbol names are replaced with underscores.  Also,
you shall not call a function you declare after 'c-library' before you
perform 'end-c-library'.

   A major benefit of these named library interfaces is that, once they
are generated, the tools used to generated them (in particular, the C
compiler and libtool) are no longer needed, so the interface can be used
even on machines that do not have the tools installed.  The build system
of Gforth can even cross-compile these libraries, so that the libraries
are available for plattforms on which build tools aren't installed.

'c-library-name' ( c-addr u --  ) gforth-0.7 "c-library-name"
   Start a C library interface with name c-addr u.

'c-library' ( "name" --  ) gforth-0.7 "c-library"
   Parsing version of 'c-library-name'

'end-c-library' ( --  ) gforth-0.7 "end-c-library"
   Finish and (if necessary) build the latest C library interface.

6.28.5 Declaring OS-level libraries
-----------------------------------

For calling some C functions, you need to link with a specific OS-level
library that contains that function.  E.g., the 'sin' function requires
linking a special library by using the command line switch '-lm'.  In
our C iterface you do the equivalent thing by calling 'add-lib' as
follows:

     clear-libs
     s" m" add-lib
     \c #include <math.h>
     c-function sin sin r -- r

   First, you clear any libraries that may have been declared earlier
(you don't need them for 'sin'); then you add the 'm' library (actually
'libm.so' or somesuch) to the currently declared libraries; you can add
as many as you need.  Finally you declare the function as shown above.
Typically you will use the same set of library declarations for many
function declarations; you need to write only one set for that, right at
the beginning.

   Note that you must not call 'clear-libs' inside
'c-library...end-c-library'; however, 'c-library' performs the function
of 'clear-libs', so 'clear-libs' is not necessary, and you usually want
to put 'add-lib' calls inside 'c-library...end-c-library'.

'clear-libs' ( --  ) gforth-0.7 "clear-libs"
   Clear the list of libs

'add-lib' ( c-addr u --  ) gforth-0.7 "add-lib"
   Add library libstring to the list of libraries, where string is
represented by c-addr u.

'add-libpath' ( c-addr u --  ) gforth-0.7 "add-libpath"
   Add path string to the list of library search pathes, where string is
represented by c-addr u.

'add-framework' ( c-addr u --  ) gforth-1.0 "add-framework"
   Add framework libstring to the list of frameworks, where string is
represented by c-addr u.

'add-incdir' ( c-addr u --  ) gforth-1.0 "add-incdir"
   Add path c-addr u to the list of include search pathes

'add-cflags' ( c-addr u --  ) gforth-1.0 "add-cflags"
   add any kind of cflags to compilation

'add-ldflags' ( c-addr u --  ) gforth-1.0 "add-ldflags"
   add flag to linker

6.28.6 Callbacks
----------------

In some cases you have to pass a function pointer to a C function, i.e.,
the library wants to call back to your application (and the pointed-to
function is called a callback function).  You can pass the address of an
existing C function (that you get with 'lib-sym', *note Low-Level C
Interface Words::), but if there is no appropriate C function, you
probably want to define the function as a Forth word.  Then you need to
generate a callback as described below:

   You can generate C callbacks from Forth code with 'c-callback'.

'c-callback' ( "forth-name" "{type}" "---" "type" --  ) gforth-1.0 "c-callback"
   Define a callback instantiator with the given signature.  The
callback instantiator forth-name '( xt -- addr )' takes an XT, and
returns the ADDRess of the C function handling that callback.

'c-callback-thread' ( "forth-name" "{type}" "---" "type" --  ) gforth-1.0 "c-callback-thread"
   Define a callback instantiator with the given signature.  The
callback instantiator forth-name '( xt -- addr )' takes an XT, and
returns the ADDRess of the C function handling that callback.  This
callback is safe when called from another thread

   This precompiles a number of callback functions (up to the value
'callback#').  The prototype of the C function is deduced from its Forth
signature.  If this is not sufficient, you can add types in curly braces
after the Forth type.

     c-callback vector4double: f f f f -- void
     c-callback vector4single: f{float} f{float} f{float} f{float} -- void

6.28.7 How the C interface works
--------------------------------

The documented C interface works by generating a C code out of the
declarations.

   In particular, for every Forth word declared with 'c-function', it
generates a wrapper function in C that takes the Forth data from the
Forth stacks, and calls the target C function with these data as
arguments.  The C compiler then performs an implicit conversion between
the Forth type from the stack, and the C type for the parameter, which
is given by the C function prototype.  After the C function returns, the
return value is likewise implicitly converted to a Forth type and
written back on the stack.

   The '\c' lines are literally included in the C code (but without the
'\c'), and provide the necessary declarations so that the C compiler
knows the C types and has enough information to perform the conversion.

   These wrapper functions are eventually compiled and dynamically
linked into Gforth, and then they can be called.

   The libraries added with 'add-lib' are used in the compile command
line to specify dependent libraries with '-lLIB', causing these
libraries to be dynamically linked when the wrapper function is linked.

6.28.8 Low-Level C Interface Words
----------------------------------

'open-lib' ( c-addr1 u1 -- u2 ) gforth-0.4 "open-lib"

'lib-sym' ( c-addr1 u1 u2 -- u3 ) gforth-0.4 "lib-sym"

'lib-error' ( -- c-addr u ) gforth-0.7 "lib-error"
   Error message for last failed 'open-lib' or 'lib-sym'.

'call-c' ( ... w -- ... ) gforth-0.2 "call-c"
   Call the C function pointed to by w.  The C function has to access
the stack itself.  The stack pointers are exported into a ptrpair
structure passed to the C function, and returned in that form.

6.28.9 Automated interface generation using SWIG
------------------------------------------------

SWIG, the Simple Wrapper Interface Generator, is used to create C
interfaces for a lot of programming languages.  The SWIG version
extended with a Forth module can be found on github
(https://github.com/GeraldWodni/swig).

6.28.9.1 Basic operation
........................

C-headers are parsed and converted to Forth-Sourcecode which uses the
previously describe C interface functions.

6.28.9.2 Detailed operation:
............................

  1. Select a target, in this example we are using 'example.h'
  2. Create an interface file for the header.  This can be used to pass
     options, switches and define variables.  In the simplest case it
     just instructs to translate all of 'example.h':
          %module example
          %insert("include")
          {
              #include "example.h"
          }
          %include "example.h"
  3. Use SWIG to create a '.fsi-c' file.
     'swig -forth -stackcomments -use-structs -enumcomments -o
     example-fsi.c example.i'.
     FSI stands "Forth Source Independent" meaning it can be transferred
     to any host having a C-compiler.  SWIG is not required past this
     point.
  4. On the target machine compile the '.fsi-c' file to a '.fsx' (x
     stands for executable)
     'gcc -o example.fsx example-fsi.c'
     The compilation will resolve all constants to the values on the
     target.
  5. The last step is to run the executable and capture its output to a
     '.fs' "Forth Source" file.
     './example.fsx -gforth > example.fs'
     This code can now be used on the target platform.

6.28.9.3 Examples
.................

You can find some examples in SWIG's Forth Example section
(https://github.com/GeraldWodni/swig/tree/master/Examples/forth).

   A lot of interface files can be found in Forth Posix C-Interface
(https://github.com/GeraldWodni/posix) and Forth C-Interface Modules
(https://github.com/GeraldWodni/forth-c-interfaces).

   Contribution to the Forth C-Interface Module repository
(https://github.com/GeraldWodni/forth-c-interfaces) is always welcome.

6.28.10 Migrating from Gforth 0.7
---------------------------------

In this version, you can use '\c', 'c-function' and 'add-lib' only
inside 'c-library'...'end-c-library'.  'add-lib' now always starts from
a clean slate inside a 'c-library', so you don't need to use
'clear-libs' in most cases.

   If you have a program that uses these words outside
'c-library'...'end-c-library', just wrap them in
'c-library'...'end-c-library'.  You may have to add some instances of
'add-lib', however.

6.29 Assembler and Code Words
=============================

6.29.1 Definitions in assembly language
---------------------------------------

Gforth provides ways to implement words in assembly language (using
'abi-code'...'end-code'), and also ways to define defining words with
arbitrary run-time behaviour (like 'does>'), where (unlike 'does>') the
behaviour is not defined in Forth, but in assembly language (with
';code').

   However, the machine-independent nature of Gforth poses a few
problems: First of all, Gforth runs on several architectures, so it can
provide no standard assembler.  It does provide assemblers for several
of the architectures it runs on, though.  Moreover, you can use a
system-independent assembler in Gforth, or compile machine code directly
with ',' and 'c,'.

   Another problem is that the virtual machine registers of Gforth (the
stack pointers and the virtual machine instruction pointer) depend on
the installation and engine.  Also, which registers are free to use also
depend on the installation and engine.  So any code written to run in
the context of the Gforth virtual machine is essentially limited to the
installation and engine it was developed for (it may run elsewhere, but
you cannot rely on that).

   Fortunately, you can define 'abi-code' words in Gforth that are
portable to any Gforth running on a platform with the same calling
convention (ABI); typically this means portability to the same
architecture/OS combination, sometimes crossing OS boundaries).

'assembler' ( --  ) tools-ext "assembler"
   A vocubulary: Replaces the wordlist at the top of the search order
with the assembler wordlist.

'init-asm' ( --  ) gforth-0.2 "init-asm"
   Pushes the assembler wordlist on the search order.

'abi-code' ( "name" -- colon-sys  ) gforth-1.0 "abi-code"
   Start a native code definition that is called using the platform's
ABI conventions corresponding to the C-prototype:
     Cell *function(Cell *sp, Float **fpp);
   The FP stack pointer is passed in by providing a reference to a
memory location containing the FP stack pointer and is passed out by
storing the changed FP stack pointer there (if necessary).

';abi-code' ( --  ) gforth-1.0 "semicolon-abi-code"
   Ends the colon definition, but at run-time also changes the last
defined word X (which must be a 'create'd word) to call the following
native code using the platform's ABI convention corresponding to the C
prototype:
      Cell *function(Cell *sp, Float **fpp, Address body);
   The FP stack pointer is passed in by providing a reference to a
memory location containing the FP stack pointer and is passed out by
storing the changed FP stack pointer there (if necessary).  The
parameter body is the body of X.

'end-code' ( colon-sys --  ) gforth-0.2 "end-code"
   End a code definition.  Note that you have to assemble the return
from the ABI call (for 'abi-code') or the dispatch to the next VM
instruction (for 'code' and ';code') yourself.

'code' ( "name" -- colon-sys  ) tools-ext "code"
   Start a native code definition that runs in the context of the Gforth
virtual machine (engine).  Such a definition is not portable between
Gforth installations, so we recommend using 'abi-code' instead of
'code'.  You have to end a 'code' definition with a dispatch to the next
virtual machine instruction.

';code' ( compilation. colon-sys1 -- colon-sys2  ) tools-ext "semicolon-code"
   The code after ';code' becomes the behaviour of the last defined word
(which must be a 'create'd word).  The same caveats apply as for 'code',
so we recommend using ';abi-code' instead.

'flush-icache' ( c-addr u -- ) gforth-0.2 "flush-icache"
   Make sure that the instruction cache of the processor (if there is
one) does not contain stale data at c-addr and u bytes afterwards.
'END-CODE' performs a 'flush-icache' automatically.  Caveat:
'flush-icache' might not work on your installation; this is usually the
case if direct threading is not supported on your machine (take a look
at your 'machine.h') and your machine has a separate instruction cache.
In such cases, 'flush-icache' does nothing instead of flushing the
instruction cache.

   If 'flush-icache' does not work correctly, 'abi-code' words etc.
will not work (reliably), either.

   The typical usage of these words can be shown most easily by analogy
to the equivalent high-level defining words:

     : foo                              abi-code foo
        <high-level Forth words>              <assembler>
     ;                                  end-code

     : bar                              : bar
        <high-level Forth words>           <high-level Forth words>
        CREATE                             CREATE
           <high-level Forth words>           <high-level Forth words>
        DOES>                              ;code
           <high-level Forth words>           <assembler>
     ;                                  end-code

   For using 'abi-code', take a look at the ABI documentation of your
platform to see how the parameters are passed (so you know where you get
the stack pointers) and how the return value is passed (so you know
where the data stack pointer is returned).  The ABI documentation also
tells you which registers are saved by the caller (caller-saved), so you
are free to destroy them in your code, and which registers have to be
preserved by the called word (callee-saved), so you have to save them
before using them, and restore them afterwards.  For some architectures
and OSs we give short summaries of the parts of the calling convention
in the appropriate sections.  More reverse-engineering oriented people
can also find out about the passing and returning of the stack pointers
through 'see abi-call'.

   Most ABIs pass the parameters through registers, but some (in
particular the most common 386 (aka IA-32) calling conventions) pass
them on the architectural stack.  The common ABIs all pass the return
value in a register.

   Other things you need to know for using 'abi-code' is that both the
data and the FP stack grow downwards (towards lower addresses) in
Gforth, with '1 cells' size per cell, and '1 floats' size per FP value.

   Here's an example of using 'abi-code' on the 386 architecture:

     abi-code my+ ( n1 n2 -- n )
     4 sp d) ax mov \ sp into return reg
     ax )    cx mov \ tos
     4 #     ax add \ update sp (pop)
     cx    ax ) add \ sec = sec+tos
     ret            \ return from my+
     end-code

   An AMD64 variant of this example can be found in *note AMD64
Assembler::.

   Here's a 386 example that deals with FP values:

     abi-code my-f+ ( r1 r2 -- r )
     8 sp d) cx mov  \ load address of fp
     cx )    dx mov  \ load fp
     .fl dx )   fld  \ r2
     8 #     dx add  \ update fp
     .fl dx )   fadd \ r1+r2
     .fl dx )   fstp \ store r
     dx    cx ) mov  \ store new fp
     4 sp d) ax mov  \ sp into return reg
     ret             \ return from my-f+
     end-code

6.29.2 Common Assembler
-----------------------

The assemblers in Gforth generally use a postfix syntax, i.e., the
instruction name follows the operands.

   The operands are passed in the usual order (the same that is used in
the manual of the architecture).  Since they all are Forth words, they
have to be separated by spaces; you can also use Forth words to compute
the operands.

   The instruction names usually end with a ','.  This makes it easier
to visually separate instructions if you put several of them on one
line; it also avoids shadowing other Forth words (e.g., 'and').

   Registers are usually specified by number; e.g., (decimal) '11'
specifies registers R11 and F11 on the Alpha architecture (which one,
depends on the instruction).  The usual names are also available, e.g.,
's2' for R11 on Alpha.

   Control flow is specified similar to normal Forth code (*note
Arbitrary control structures::), with 'if,', 'ahead,', 'then,',
'begin,', 'until,', 'again,', 'cs-roll', 'cs-pick', 'else,', 'while,',
and 'repeat,'.  The conditions are specified in a way specific to each
assembler.

   The rest of this section is of interest mainly for those who want to
define 'code' words (instead of the more portable 'abi-code' words).

   Note that the register assignments of the Gforth engine can change
between Gforth versions, or even between different compilations of the
same Gforth version (e.g., if you use a different GCC version).  If you
are using 'CODE' instead of 'ABI-CODE', and you want to refer to
Gforth's registers (e.g., the stack pointer or TOS), I recommend
defining your own words for refering to these registers, and using them
later on; then you can adapt to a changed register assignment.

   The most common use of these registers is to end a 'code' definition
with a dispatch to the next word (the 'next' routine).  A portable way
to do this is to jump to '' noop >code-address' (of course, this is less
efficient than integrating the 'next' code and scheduling it well).
When using 'ABI-CODE', you can just assemble a normal subroutine return
(but make sure you return the data stack pointer).

   Another difference between Gforth versions is that the top of stack
is kept in memory in 'gforth' and, on most platforms, in a register in
'gforth-fast'.  For 'ABI-CODE' definitions, any stack caching registers
are guaranteed to be flushed to the stack, allowing you to reliably
access the top of stack in memory.

6.29.3 Common Disassembler
--------------------------

You can disassemble a 'code' word with 'see' (*note Debugging::).  You
can disassemble a section of memory with

'discode' ( addr u --  ) gforth-0.2 "discode"
   hook for the disassembler: disassemble u bytes of code at addr

   There are two kinds of disassembler for Gforth: The Forth
disassembler (available on some CPUs) and the gdb disassembler
(available on platforms with 'gdb' and 'mktemp').  If both are
available, the Forth disassembler is used by default.  If you prefer the
gdb disassembler, say

     ' disasm-gdb is discode

   If neither is available, 'discode' performs 'dump'.

   The Forth disassembler generally produces output that can be fed into
the assembler (i.e., same syntax, etc.).  It also includes additional
information in comments.  In particular, the address of the instruction
is given in a comment before the instruction.

   The gdb disassembler produces output in the same format as the gdb
'disassemble' command (*note Source and machine code: (gdb)Machine
Code.), in the default flavour (AT&T syntax for the 386 and AMD64
architectures).

   'See' may display more or less than the actual code of the word,
because the recognition of the end of the code is unreliable.  You can
use 'discode' if it did not display enough.  It may display more, if the
code word is not immediately followed by a named word.  If you have
something else there, you can follow the word with 'align latest ,' to
ensure that the end is recognized.

6.29.4 386 Assembler
--------------------

The 386 assembler included in Gforth was written by Bernd Paysan, it's
available under GPL, and originally part of bigFORTH.

   The 386 disassembler included in Gforth was written by Andrew McKewan
and is in the public domain.

   The disassembler displays code in an Intel-like prefix syntax.

   The assembler uses a postfix syntax with AT&T-style parameter order
(i.e., destination last).

   The assembler includes all instruction of the Athlon, i.e.  486 core
instructions, Pentium and PPro extensions, floating point, MMX, 3Dnow!,
but not ISSE. It's an integrated 16- and 32-bit assembler.  Default is
32 bit, you can switch to 16 bit with .86 and back to 32 bit with .386.

   There are several prefixes to switch between different operation
sizes, '.b' for byte accesses, '.w' for word accesses, '.d' for
double-word accesses.  Addressing modes can be switched with '.wa' for
16 bit addresses, and '.da' for 32 bit addresses.  You don't need a
prefix for byte register names ('AL' et al).

   For floating point operations, the prefixes are '.fs' (IEEE single),
'.fl' (IEEE double), '.fx' (extended), '.fw' (word), '.fd'
(double-word), and '.fq' (quad-word).  The default is '.fx', so you need
to specify '.fl' explicitly when dealing with Gforth FP values.

   The MMX opcodes don't have size prefixes, they are spelled out like
in the Intel assembler.  Instead of move from and to memory, there are
PLDQ/PLDD and PSTQ/PSTD.

   The registers lack the 'e' prefix; even in 32 bit mode, eax is called
ax.  Immediate values are indicated by postfixing them with '#', e.g.,
'3 #'.  Here are some examples of addressing modes in various syntaxes:

     Gforth          Intel (NASM)   AT&T (gas)      Name
     .w ax           ax             %ax             register (16 bit)
     ax              eax            %eax            register (32 bit)
     3 #             offset 3       $3              immediate
     1000 #)         byte ptr 1000  1000            displacement
     bx )            [ebx]          (%ebx)          base
     100 di d)       100[edi]       100(%edi)       base+displacement
     20 ax *4 i#)    20[eax*4]      20(,%eax,4)     (index*scale)+displacement
     di ax *4 i)     [edi][eax*4]   (%edi,%eax,4)   base+(index*scale)
     4 bx cx di)     4[ebx][ecx]    4(%ebx,%ecx)    base+index+displacement
     12 sp ax *2 di) 12[esp][eax*2] 12(%esp,%eax,2) base+(index*scale)+displacement

   You can use 'L)' and 'LI)' instead of 'D)' and 'DI)' to enforce
32-bit displacement fields (useful for later patching).

   Some example of instructions are:

     ax bx mov             \ move ebx,eax
     3 # ax mov            \ mov eax,3
     100 di d) ax mov      \ mov eax,100[edi]
     4 bx cx di) ax mov    \ mov eax,4[ebx][ecx]
     .w ax bx mov          \ mov bx,ax

   The following forms are supported for binary instructions:

     <reg> <reg> <inst>
     <n> # <reg> <inst>
     <mem> <reg> <inst>
     <reg> <mem> <inst>
     <n> # <mem> <inst>

   The shift/rotate syntax is:

     <reg/mem> 1 # shl \ shortens to shift without immediate
     <reg/mem> 4 # shl
     <reg/mem> cl shl

   Precede string instructions ('movs' etc.)  with '.b' to get the byte
version.

   The control structure words 'IF' 'UNTIL' etc.  must be preceded by
one of these conditions: 'vs vc u< u>= 0= 0<> u<= u> 0< 0>= ps pc < >=
<= >'.  (Note that most of these words shadow some Forth words when
'assembler' is in front of 'forth' in the search path, e.g., in 'code'
words).  Currently the control structure words use one stack item, so
you have to use 'roll' instead of 'cs-roll' to shuffle them (you can
also use 'swap' etc.).

   Based on the Intel ABI (used in Linux), 'abi-code' words can find the
data stack pointer at '4 sp d)', and the address of the FP stack pointer
at '8 sp d)'; the data stack pointer is returned in 'ax'; 'Ax', 'cx',
and 'dx' are caller-saved, so you do not need to preserve their values
inside the word.  You can return from the word with 'ret', the
parameters are cleaned up by the caller.

   For examples of 386 'abi-code' words, see *note Assembler
Definitions::.

6.29.5 AMD64 (x86_64) Assembler
-------------------------------

The AMD64 assembler is a slightly modified version of the 386 assembler,
and as such shares most of the syntax.  Two new prefixes, '.q' and
'.qa', are provided to select 64-bit operand and address sizes
respectively.  64-bit sizes are the default, so normally you only have
to use the other prefixes.  Also there are additional register operands
'R8'-'R15'.

   The registers lack the 'e' or 'r' prefix; even in 64 bit mode, 'rax'
is called 'ax'.  Additional register operands are available to refer to
the lowest-significant byte of all registers: 'R8L'-'R15L', 'SPL',
'BPL', 'SIL', 'DIL'.

   The Linux-AMD64 calling convention is to pass the first 6 integer
parameters in rdi, rsi, rdx, rcx, r8 and r9 and to return the result in
rax and rdx; to pass the first 8 FP parameters in xmm0--xmm7 and to
return FP results in xmm0--xmm1.  So 'abi-code' words get the data stack
pointer in 'di' and the address of the FP stack pointer in 'si', and
return the data stack pointer in 'ax'.  The other caller-saved registers
are: r10, r11, xmm8-xmm15.  This calling convention reportedly is also
used in other non-Microsoft OSs.

   Windows x64 passes the first four integer parameters in rcx, rdx, r8
and r9 and return the integer result in rax.  The other caller-saved
registers are r10 and r11.

   On the Linux platform, according to
<https://uclibc.org/docs/psABI-x86_64.pdf> page 21 the registers AX CX
DX SI DI R8 R9 R10 R11 are available for scratch.

   The addressing modes for the AMD64 are:

     \ running word A produces a memory error as the registers are not initialised ;-)
     ABI-CODE A  ( -- )
         500        #               AX  MOV     \ immediate
             DX              AX  MOV     \ register
             200             AX  MOV     \ direct addressing
             DX  )           AX  MOV     \ indirect addressing
         40  DX  D)          AX  MOV     \ base with displacement
             DX  CX      I)  AX  MOV     \ scaled index
             DX  CX  *4  I)  AX  MOV     \ scaled index
         40  DX  CX  *4  DI) AX  MOV     \ scaled index with displacement

             DI              AX  MOV     \ SP Out := SP in
                                 RET
     END-CODE

   Here are a few examples of an AMD64 'abi-code' words:

     abi-code my+  ( n1 n2 -- n3 )
     \ SP passed in di, returned in ax,  address of FP passed in si
     8 di d) ax lea        \ compute new sp in result reg
     di )    dx mov        \ get old tos
     dx    ax ) add        \ add to new tos
     ret
     end-code

     \ Do nothing
     ABI-CODE aNOP  ( -- )
            DI  )       AX      LEA          \ SP out := SP in
                                RET
     END-CODE

     \ Drop TOS
     ABI-CODE aDROP  ( n -- )
        8   DI  D)      AX      LEA          \ SPout := SPin - 1
                                RET
     END-CODE

     \ Push 5 on the data stack
     ABI-CODE aFIVE   ( -- 5 )
        -8  DI  D)      AX      LEA          \ SPout := SPin + 1
        5   #           AX  )   MOV          \ TOS := 5
                                RET
     END-CODE

     \ Push 10 and 20 into data stack
     ABI-CODE aTOS2  ( -- n n )
        -16 DI  D)      AX      LEA          \ SPout := SPin + 2
        10  #       8   AX  D)  MOV          \ TOS - 1 := 10
        20  #           AX  )   MOV          \ TOS := 20
                                RET
     END-CODE

     \ Get Time Stamp Counter as two 32 bit integers
     \ The TSC is incremented every CPU clock pulse
     ABI-CODE aRDTSC   ( -- TSCl TSCh )
                                RDTSC        \ DX:AX := TSC
        $FFFFFFFF #     AX      AND          \ Clear upper 32 bit AX
       0xFFFFFFFF #     DX      AND          \ Clear upper 32 bit DX
            AX          R8      MOV          \ Tempory save AX
        -16 DI  D)      AX      LEA          \ SPout := SPin + 2
            R8      8   AX  D)  MOV          \ TOS-1 := saved AX = TSC low
            DX          AX  )   MOV          \ TOS := Dx = TSC high
                                RET
     END-CODE

     \ Get Time Stamp Counter as 64 bit integer
     ABI-CODE RDTSC   ( -- TSC )
                                RDTSC        \ DX:AX := TSC
        $FFFFFFFF #     AX      AND          \ Clear upper 32 bit AX
        32  #           DX      SHL          \ Move lower 32 bit DX to upper 32 bit
            AX          DX      OR           \ Combine AX wit DX in DX
        -8  DI  D)      AX      LEA          \ SPout := SPin + 1
            DX          AX  )   MOV          \ TOS := DX
                                RET
     END-CODE

     VARIABLE V

     \ Assign 4 to variable V
     ABI-CODE V=4 ( -- )
            BX                  PUSH         \ Save BX, used by gforth
        V   #           BX      MOV          \ BX := address of V
        4   #           BX )    MOV          \ Write 4 to V
            BX                  POP          \ Restore BX
            DI  )       AX      LEA          \ SPout := SPin
                                RET
     END-CODE

     VARIABLE V

     \ Assign 5 to variable V
     ABI-CODE V=5 ( -- )
        V   #           CX      MOV          \ CX := address of V
        5   #           CX )    MOV          \ Write 5 to V
        DI )            AX      LEA          \ SPout := SPin
                                RET
     END-CODE

     ABI-CODE TEST2  ( -- n n )
        -16 DI  D)  AX          LEA          \ SPout := SPin + 2
        5   #       CX          MOV          \ CX := 5
        5   #       CX          CMP
        0= IF
            1   #   8   AX  D)      MOV      \ If CX = 5 then TOS - 1 := 1  <--
        ELSE
            2   #   8   AX  D)      MOV      \ else TOS - 1 := 2
        THEN
        6   #       CX          CMP
        0= IF
            3   #       AX  )       MOV      \ If CX = 6 then TOS := 3
        ELSE
            4   #       AX  )       MOV      \ else TOS := 4  <--
        THEN
                                RET
     END-CODE

     \ Do four loops. Expect : ( 4 3 2 1 -- )
     ABI-CODE LOOP4  ( -- n n n n )
            DI          AX      MOV          \ SPout := SPin
        4   #           DX      MOV          \ DX := 4  loop counter
        BEGIN
            8   #           AX      SUB      \ SP := SP + 1
                DX          AX  )   MOV      \ TOS := DX
            1   #           DX      SUB      \ DX := DX - 1
        0= UNTIL
                                RET
     END-CODE

   Here's a AMD64 example that deals with FP values:

     abi-code my-f+  ( r1 r2 -- r )
     \ SP passed in di, returned in ax,  address of FP passed in si
     si )       dx mov         \ load fp
     8 dx d)  xmm0 movsd       \ r2
     dx )     xmm0 addsd       \ r1+r2
     xmm0  8 dx d) movsd       \ store r
     8 #      si ) add         \ update fp
     di         ax mov         \ sp into return reg
     ret
     end-code

6.29.6 Alpha Assembler
----------------------

The Alpha assembler and disassembler were originally written by Bernd
Thallner.

   The register names 'a0'--'a5' are not available to avoid shadowing hex
numbers.

   Immediate forms of arithmetic instructions are distinguished by a '#'
just before the ',', e.g., 'and#,' (note: 'lda,' does not count as
arithmetic instruction).

   You have to specify all operands to an instruction, even those that
other assemblers consider optional, e.g., the destination register for
'br,', or the destination register and hint for 'jmp,'.

   You can specify conditions for 'if,' by removing the first 'b' and
the trailing ',' from a branch with a corresponding name; e.g.,

     11 fgt if, \ if F11>0e
       ...
     endif,

   'fbgt,' gives 'fgt'.

6.29.7 MIPS assembler
---------------------

The MIPS assembler was originally written by Christian Pirker.

   Currently the assembler and disassembler covers most of the MIPS32
architecture and doesn't support FP instructions.

   The register names '$a0'--'$a3' are not available to avoid shadowing
hex numbers.  Use register numbers '$4'--'$7' instead.

   Nothing distinguishes registers from immediate values.  Use explicit
opcode names with the 'i' suffix for instructions with immediate
argument.  E.g.  'addiu,' in place of 'addu,'.

   Where the architecture manual specifies several formats for the
instruction (e.g., for 'jalr,'),use the one with more arguments (i.e.
two for 'jalr,').  When in doubt, see 'arch/mips/testasm.fs' for an
example of correct use.

   Branches and jumps in the MIPS architecture have a delay slot.  You
have to fill it manually (the simplest way is to use 'nop,'), the
assembler does not do it for you (unlike 'as').  Even 'if,', 'ahead,',
'until,', 'again,', 'while,', 'else,' and 'repeat,' need a delay slot.
Since 'begin,' and 'then,' just specify branch targets, they are not
affected.  For branches the argument specifying the target is a relative
address.  Add the address of the delay slot to get the absolute address.

   Note that you must not put branches nor jumps (nor control-flow
instructions) into the delay slot.  Also it is a bad idea to put
pseudo-ops such as 'li,' into a delay slot, as these may expand to
several instructions.  The MIPS I architecture also had load delay
slots, and newer MIPSes still have restrictions on using 'mfhi,' and
'mflo,'.  Be careful to satisfy these restrictions, the assembler does
not do it for you.

   Some example of instructions are:

     $ra  12 $sp  sw,         \ sw    ra,12(sp)
     $4    8 $s0  lw,         \ lw    a0,8(s0)
     $v0  $0  lui,            \ lui   v0,0x0
     $s0  $s4  $12  addiu,    \ addiu s0,s4,0x12
     $s0  $s4  $4  addu,      \ addu  s0,s4,$a0
     $ra  $t9  jalr,          \ jalr  t9

   You can specify the conditions for 'if,' etc.  by taking a
conditional branch and leaving away the 'b' at the start and the ',' at
the end.  E.g.,

     4 5 eq if,
       ... \ do something if $4 equals $5
     then,

   The calling conventions for 32-bit MIPS machines is to pass the first
4 arguments in registers '$4'..'$7', and to use '$v0'-'$v1' for return
values.  In addition to these registers, it is ok to clobber registers
'$t0'-'$t8' without saving and restoring them.

   If you use 'jalr,' to call into dynamic library routines, you must
first load the called function's address into '$t9', which is used by
position-indirect code to do relative memory accesses.

   Here is an example of a MIPS32 'abi-code' word:

     abi-code my+  ( n1 n2 -- n3 )
       \ SP passed in $4, returned in $v0
       $t0  4 $4  lw,         \ load n1, n2 from stack
       $t1  0 $4  lw,
       $t0  $t0  $t1  addu,   \ add n1+n2, result in $t0
       $t0  4 $4  sw,         \ store result (overwriting n1)
       $ra  jr,               \ return to caller
       $v0  $4  4  addiu,     \ (delay slot) return uptated SP in $v0
     end-code

6.29.8 PowerPC assembler
------------------------

The PowerPC assembler and disassembler were contributed by Michal
Revucky.

   This assembler does not follow the convention of ending mnemonic
names with a ",", so some mnemonic names shadow regular Forth words (in
particular: 'and or xor fabs'); so if you want to use the Forth words,
you have to make them visible first, e.g., with 'also forth'.

   Registers are referred to by their number, e.g., '9' means the
integer register 9 or the FP register 9 (depending on the instruction).

   Because there is no way to distinguish registers from immediate
values, you have to explicitly use the immediate forms of instructions,
i.e., 'addi,', not just 'add,'.

   The assembler and disassembler usually support the most general form
of an instruction, but usually not the shorter forms (especially for
branches).

6.29.9 ARM Assembler
--------------------

The ARM assembler includes all instruction of ARM architecture version
4, and the BLX instruction from architecture 5.  It does not (yet) have
support for Thumb instructions.  It also lacks support for any
co-processors.

   The assembler uses a postfix syntax with the same operand order as
used in the ARM Architecture Reference Manual.  Mnemonics are suffixed
by a comma.

   Registers are specified by their names 'r0' through 'r15', with the
aliases 'pc', 'lr', 'sp', 'ip' and 'fp' provided for convenience.  Note
that 'ip' refers to the"intra procedure call scratch register" ('r12')
and does not refer to an instruction pointer.  'sp' refers to the ARM
ABI stack pointer ('r13') and not the Forth stack pointer.

   Condition codes can be specified anywhere in the instruction, but
will be most readable if specified just in front of the mnemonic.  The
'S' flag is not a separate word, but encoded into instruction mnemonics,
ie.  just use 'adds,' instead of 'add,' if you want the status register
to be updated.

   The following table lists the syntax of operands for general
instructions:

     Gforth          normal assembler      description
     123 #           #123                  immediate
     r12             r12                   register
     r12 4 #LSL      r12, LSL #4           shift left by immediate
     r12 r1 LSL      r12, LSL r1           shift left by register
     r12 4 #LSR      r12, LSR #4           shift right by immediate
     r12 r1 LSR      r12, LSR r1           shift right by register
     r12 4 #ASR      r12, ASR #4           arithmetic shift right
     r12 r1 ASR      r12, ASR r1           ... by register
     r12 4 #ROR      r12, ROR #4           rotate right by immediate
     r12 r1 ROR      r12, ROR r1           ... by register
     r12 RRX         r12, RRX              rotate right with extend by 1

   Memory operand syntax is listed in this table:

     Gforth            normal assembler      description
     r4 ]              [r4]                  register
     r4 4 #]           [r4, #+4]             register with immediate offset
     r4 -4 #]          [r4, #-4]             with negative offset
     r4 r1 +]          [r4, +r1]             register with register offset
     r4 r1 -]          [r4, -r1]             with negated register offset
     r4 r1 2 #LSL -]   [r4, -r1, LSL #2]     with negated and shifted offset
     r4 4 #]!          [r4, #+4]!            immediate preincrement
     r4 r1 +]!         [r4, +r1]!            register preincrement
     r4 r1 -]!         [r4, +r1]!            register predecrement
     r4 r1 2 #LSL +]!  [r4, +r1, LSL #2]!    shifted preincrement
     r4 -4 ]#          [r4], #-4             immediate postdecrement
     r4 r1 ]+          [r4], r1              register postincrement
     r4 r1 ]-          [r4], -r1             register postdecrement
     r4 r1 2 #LSL ]-   [r4], -r1, LSL #2     shifted postdecrement
     ' xyz >body [#]   xyz                   PC-relative addressing

   Register lists for load/store multiple instructions are started and
terminated by using the words '{' and '}' respectively.  Between braces,
register names can be listed one by one or register ranges can be formed
by using the postfix operator 'r-r'.  The '^' flag is not encoded in the
register list operand, but instead directly encoded into the instruction
mnemonic, ie.  use '^ldm,' and '^stm,'.

   Addressing modes for load/store multiple are not encoded as
instruction suffixes, but instead specified like an addressing mode, Use
one of 'DA', 'IA', 'DB', 'IB', 'DA!', 'IA!', 'DB!' or 'IB!'.

   The following table gives some examples:

     Gforth                           normal assembler
     r4 ia  { r0 r7 r8 }  stm,        stmia    r4, {r0,r7,r8}
     r4 db!  { r0 r7 r8 }  ldm,       ldmdb    r4!, {r0,r7,r8}
     sp ia!  { r0 r15 r-r }  ^ldm,    ldmfd    sp!, {r0-r15}^

   Control structure words typical for Forth assemblers are available:
'if,' 'ahead,' 'then,' 'else,' 'begin,' 'until,' 'again,' 'while,'
'repeat,' 'repeat-until,'.  Conditions are specified in front of these
words:

     r1 r2 cmp,    \ compare r1 and r2
     eq if,        \ equal?
        ...          \ code executed if r1 == r2
     then,

   Example of a definition using the ARM assembler:

     abi-code my+ ( n1 n2 --  n3 )
        \ arm abi: r0=SP, r1=&FP, r2,r3,r12 saved by caller
        r0 IA!  { r2 r3 }  ldm,     \ pop r2 = n2, r3 = n1
        r3  r2  r3         add,     \ r3 = n1+n1
        r3  r0 -4 #]!      str,     \ push r3
        pc  lr             mov,     \ return to caller, new SP in r0
     end-code

6.29.10 Other assemblers
------------------------

If you want to contribute another assembler/disassembler, please contact
us (<anton@mips.complang.tuwien.ac.at>) to check if we have such an
assembler already.  If you are writing them from scratch, please use a
similar syntax style as the one we use (i.e., postfix, commas at the end
of the instruction names, *note Common Assembler::); make the output of
the disassembler be valid input for the assembler, and keep the style
similar to the style we used.

   Hints on implementation: The most important part is to have a good
test suite that contains all instructions.  Once you have that, the rest
is easy.  For actual coding you can take a look at 'arch/mips/disasm.fs'
to get some ideas on how to use data for both the assembler and
disassembler, avoiding redundancy and some potential bugs.  You can also
look at that file (and *note Advanced does> usage example::) to get
ideas how to factor a disassembler.

   Start with the disassembler, because it's easier to reuse data from
the disassembler for the assembler than the other way round.

   For the assembler, take a look at 'arch/alpha/asm.fs', which shows
how simple it can be.

6.30 Carnal words
=================

These words deal with the mechanics of Gforth (in Forth circles called
"carnal knowledge" of a Forth system), but we consider them stable
enough to document them.

6.30.1 Header fields
--------------------

In Gforth 1.0 we switched to a new word header layout.  For a detailed
description, read: Bernd Paysan and M. Anton Ertl.  'The new Gforth
header (http://www.euroforth.org/ef19/papers/paysan.pdf)'.  In 35th
EuroForth Conference, pages 5-20, 2019.  Since this paper was published,
xt and nt have been changed to point to the parameter field, like the
body, but otherwise it is still up-to-date.

   This section explains just the data structure and the words used to
access it.  A header has the following fields:

     name
     >f+c
     >link
     >cfa
     >namehm
     >body

   Currently Gforth has the names shown above for getting from the
xt/nt/body to the field, but apart from the standard '>body' they are
not stable Gforth words.  Instead, we provide access words.  Note that
the documented access words have survived the reorganization of the
header layout.

   Some of the words expect an nt, some expect an xt.  Given that both
nt and xt point to the body of a word, what is the difference?  For most
words, the xt and nt use the same header, and with nt=xt, they point to
the same place.  However, for a synonym (*note Aliases::) there is a
difference; consider the example

     create x
     synonym y x
     synonym z y

   In this case the nt of 'z' points to the body of 'z', while the xt of
'z' points to the body of 'x'.  Words defined with 'alias' or 'forward'
(*note Forward::) also have different nts and xts.

   The name field is variable-length and is accessed with 'name>string'
(*note Name token::).

   The '>f+c' field contains flags and the name length (count).  You
read the count with 'name>string', and the flags with

'compile-only?' ( nt -- flag  ) gforth-1.0 "compile-only?"
   true if nt is marked as compile-only.

   The '>link' field contains a link to the previous word in the same
word list.  You can read it with 'name>link' (*note Name token::).

   The name, '>f+c' and '>link' fields are not present for 'noname'
words, but 'name>string' and 'name>link' work nevertheless, producing 0
0 and 0, respectively.

   The '>cfa' field (aka code field) contains the code address used for
'execute'ing the word; you can read it with '>code-address' and write it
with 'code-address!' (*note Threading Words::).

   The '>namehm' field contains the address of the header methods table,
described below.  You access it by performing or accessing header
methods (*note Header methods::).

   The '>body' (aka parameter) field contains data or threaded code
specific to the word type; its length depends on the word type.  E.g.,
for a 'constant' it contains a cell with the value of the constant.  You
can access it through '>body' (*note CREATE..DOES> details::), but this
is only standard for words you defined with 'create'.

6.30.2 Header methods
---------------------

The new Gforth word header is object-oriented and supports the following
methods (method selectors):

     .hm label method          overrider        field
               execute         set-execute      >cfa
     opt:      opt-compile,    set-optimizer    >hmcompile,
     to:       defer!          set-to           >hmto
     defer@:   defer@          set-defer@       >hmdefer@
     extra:                                     >hmextra
     >int:     name>interpret  set->int         >hm>int
     >comp:    name>compile    set->comp        >hm>comp
     >string:  name>string     set-name>string  >hm>string
     >link:    name>link       set-name>link    >hm>link

   Many of these words are not stable Gforth words, but Gforth has
stable higher-level words that we mention below.

   You can look at the header methods of a word with

'.hm' ( nt --  ) gforth-1.0 "dot-h-m"
   print the header methods of nt

   Overrider (setter) words change the method implementation for the
most recent definition.  Quotations or closures restore the previous
most recent definition when they are completed, so they are not
considered most recent, and you can do things like:

     : my2dup over over ;
     [: drop ]] over over [[ ;] set-optimizer

   The 'execute' method is actually stored in the '>cfa' field in the
header rather than in the header-methods table for performance reasons;
also it is implemented through a native-code address, while the other
methods are implemented by calling an xt.  The high-level way to set
this method is

'set-execute' ( ca --  ) gforth-1.0 "set-execute"
   Changes the current word such that it jumps to the native code at ca.
Also changes the 'compile,' implementation to the most general (and
slowest) one.  Call 'set-optimizer' afterwards if you want a more
efficient 'compile,' implementation.

   To get a code address for use with 'set-execute', you can use words
like 'docol:' or '>code-address', *Note Threading Words::.

   As an alternative to 'set-execute', there is also 'set-does>' (*note
User-defined Defining Words::), which takes an xt.

   Moreover, there are the low-level 'code-address!' and 'definer!'
(*note Threading Words::).

   The 'opt-compile,' method is what 'compile,' does on most Gforth
engines ('gforth-itc' uses ',' instead).  You can define a more
efficient implementation of 'compile,' for the current word with
'set-optimizer' (*note User-defined compile-comma::).  Note that the end
result must be equivalent to 'postpone literal postpone execute'.

   As an example of the use of 'set-optimizer', consider the following
definition of 'constant':

     : constant ( n "name" -- ; name: -- n )
       create ,
       ['] @ set-does>
     ;

     5 constant five
     : foo five ; see foo

   The Forth system does not know that the value of a constant must not
be changed, and just sees a 'create'd word (which can be changed with
'>body'), and 'foo' first pushes the body address of 'five' and then
fetches from there.  With 'set-optimizer' the definition of 'constant'
can be optimized as follows:

     : constant ( n "name" -- ; name: -- n )
       create ,
       ['] @ set-does>
       [: >body @ postpone literal ;] set-optimizer
     ;

   Now 'foo' contains the literal 5 rather than a call to 'five'.

   Note that 'set-execute' and 'set-does>' perform 'set-optimizer'
themselves in order to ensure that 'execute' and 'compile,' agree, so if
you want to add your own optimizer, you should add it afterwards.

   The 'defer!' (aka '(to)' method (*note User-defined TO and DEFER@::)
implements 'defer!' for words defined with 'defer' and similar words,
but it is also the core of 'to'.  The general stack effect of the
'defer!'/'(to)' method is '( val xt -- )', where xt identifies the word
stored into, and val is the value (of appropriate type) stored there.

   E.g., one can implement 'fvalue' as follows:

     : fvalue-to ( r xt -- ) >body f! ;

     : fvalue ( r -- )
       create f,
       ['] f@ set-does>
       ['] fvalue-to set-to ;

     5e fvalue foo
     : bar foo 1e f+ to foo ;
     see bar

   You can improve the generated code with 'set-optimizer':

     : compile-fvalue-to ( xt-value-to -- )
       drop ]] >body f! [[ ;

     : fvalue-to ( r xt -- ) >body f! ;
     ' compile-fvalue-to set-optimizer

     : fvalue ( r -- )
       create f,
       ['] f@ set-does>
       [: >body ]] literal f@ [[ ;] set-optimizer
       ['] fvalue-to set-to ;

     5e fvalue foo
     : bar foo 1e f+ to foo ;
     see bar

   In practice Gforth has a few additional twists to implement, e.g.,
'+TO'.

   'Set-defer@' (*note User-defined TO and DEFER@::) allows to implement
variants of the 'defer@' (*note Deferred Words::) method for
'defer'-like words.

   The '>hmextra' field is used for cases where additional data needs to
be stored in the header methods table.  In particular, it stores the xt
passed to 'set-does>' (and 'does>' calls 'set-does>') and the code
address behind ';abi-code'.

   The methods above all consume an xt, not an nt, but the override
words work on the most recent definition.  This means that if you use,
e.g., 'set-optimizer' on a synonym, the effect will probably not be what
you intended: When 'compile,'ing the xt of the word, the 'opt-compile,'
implementation of the original word will be used, not the freshly-set
one of the synonym.

   The following methods consume an nt.

   The 'name>interpret' method is implemented as noop for most words,
except synonyms and similar words.

'set->int' ( xt --  ) gforth-1.0 "set-to-int"
   Sets the implementation of the 'name>interpret ( nt -- xt2 )' method
of the current word to xt.

   The 'name>compile' method produces the compilation semantics of the
nt.  By changing it with 'set->comp', you can change the compilation
semantics, but it's not as simple as just pushing the xt of the desired
compilation semantics, because of the stack effect of 'name>compile'.
Generally you should avoid changing the compilation semantics, and if
you do, use a higher-level word like 'immediate' or
'interpret/compile:', *Note Combined words::.

'set->comp' ( xt --  ) gforth-1.0 "set-to-comp"
   Sets the implementation of the 'name>compile ( nt -- w xt2 )' method
of the current word to xt.

'immediate?' ( nt -- flag  ) gforth-1.0 "immediate?"
   true if the word nt has non-default compilation semantics (that's not
quite according to the definition of immediacy, but many people mean
that when they call a word "immediate").

   'Name>string' and 'Name>link' are methods in order to make it
possible to eliminate the name, '>f+c' and 'link' fields from noname
headers, but still produce meaningful results when using these words.
You will typically not change the implementations of these methods
except with 'noname', but we still have

'set-name>string' ( xt --  ) gforth-1.0 "set-name-to-string"
   Sets the implementation of the 'name>string ( nt -- addr u )' method
of the current word to xt.

'set-name>link' ( xt --  ) gforth-1.0 "set-name-to-link"
   Sets the implementation of the 'name>link ( nt1 -- nt2|0 )' method of
the current word to xt.

6.30.3 Threading Words
----------------------

The terminology used here stems from indirect threaded Forth systems; in
such a system, the XT of a word is represented by the CFA (code field
address) of a word; the CFA points to a cell that contains the code
address.  The code address is the address of some machine code that
performs the run-time action of invoking the word (e.g., the 'dovar:'
routine pushes the address of the body of the word (a variable) on the
stack).

   These words provide access to code fields, code addresses and other
threading stuff in Gforth.  It more or less abstracts away the
differences between direct and indirect threading.

   Up to and including Gforth 0.7, the code address (plus, for
'does>'-defined words, the address returned by '>does-code') was
sufficient to know the type of the word.  However, since Gforth-1.0 the
behaviour or at least implementation of words like 'compile,' and
'name>compile' can be determined independently as described in *note
Header methods::.

   The following words for create a code field and at the same time
initialize the header methods:

'hmcopy,' ( xt --  ) gforth-experimental "hmcopy-comma"
   While constructing a header, allocate the code field, and use xt as
prototype for setting the code field and the header methods.

'docol,' ( --  ) gforth-1.0 "docol,"
   The code address of a colon definition.

'docon,' ( --  ) gforth-1.0 "docon,"
   The code address of a 'CONSTANT'.

'dovar,' ( --  ) gforth-1.0 "dovar,"
   The code address of a 'CREATE'd word.

'douser,' ( --  ) gforth-1.0 "douser,"
   The code address of a 'USER' variable.

'dodefer,' ( --  ) gforth-1.0 "dodefer,"
   The code address of a 'defer'ed word.

'dofield,' ( --  ) gforth-1.0 "dofield,"
   The code address of a 'field'.

'dovalue,' ( --  ) gforth-1.0 "dovalue,"
   The code address of a 'CONSTANT'.

'doabicode,' ( --  ) gforth-1.0 "doabicode,"
   The code address of a 'ABI-CODE' definition.

   For 'does>'-defined words, use 'hmcopy,'.

   Or you use a higher-level word like 'create-from' (*note Creating
from a prototype::).

   The following words were designed before the introduction of header
methods, and are therefore not the best (and recommended) way to deal
with different word types in Gforth.

   In an indirect threaded Forth, you can get the code address of name
with '' name @'; in Gforth you can get it with '' name >code-address',
independent of the threading method.

'threading-method' ( -- n ) gforth-0.2 "threading-method"
   0 if the engine is direct threaded.  Note that this may change during
the lifetime of an image.

'>code-address' ( xt -- c_addr  ) gforth-0.2 ">code-address"
   c-addr is the code address of the word xt.

'code-address!' ( c_addr xt --  ) gforth-obsolete "code-address!"
   Change a code field with code address c-addr at xt.

   The code addresses produced by various defining words are produced by
the following words:

'docol:' ( -- addr  ) gforth-0.2 "docol:"
   The code address of a colon definition.

'docon:' ( -- addr  ) gforth-0.2 "docon:"
   The code address of a 'CONSTANT'.

'dovar:' ( -- addr  ) gforth-0.2 "dovar:"
   The code address of a 'CREATE'd word.

'douser:' ( -- addr  ) gforth-0.2 "douser:"
   The code address of a 'USER' variable.

'dodefer:' ( -- addr  ) gforth-0.2 "dodefer:"
   The code address of a 'defer'ed word.

'dofield:' ( -- addr  ) gforth-0.2 "dofield:"
   The code address of a 'field'.

'dovalue:' ( -- addr  ) gforth-0.7 "dovalue:"
   The code address of a 'CONSTANT'.

'dodoes:' ( -- addr  ) gforth-0.6 "dodoes:"
   The code address of a 'DOES>'-defined word.

'doabicode:' ( -- addr  ) gforth-1.0 "doabicode:"
   The code address of a 'ABI-CODE' definition.

   For a word X defined with 'set-does>', the code address points to
'dodoes:', and the '>hmextra' field of the header methods contains the
xt of the word that is called after pushing the body addres of X.

   If you want to know whether a word is a 'DOES>'-defined word, and
what Forth code it executes, '>does-code' tells you that:

'>does-code' ( xt1 -- xt2  ) gforth-0.2 ">does-code"
   If xt1 is the execution token of a child of a 'set-does>'-defined
word, xt2 is the xt passed to 'set-does>', i.e, the xt of the word that
is executed when executing xt1 (but first the body address of xt1 is
pushed).  If xt1 does not belong to a 'set-does>'-defined word, xt2 is
0.

   You can use the resulting xt2 with 'set-does>' (preferred) to change
the latest word or with

'does-code!' ( xt2 xt1 --  ) gforth-0.2 "does-code!"
   Change xt1 to be a 'xt2 set-does>'-defined word.

   to change an arbitrary word.

   The following two words generalize '>code-address', '>does-code',
'code-address!', and 'does-code!':

'>definer' ( xt -- definer  ) gforth-0.2 ">definer"
   DEFINER is a unique identifier for the way the XT was defined.  Words
defined with different 'does>'-codes have different definers.  The
definer can be used for comparison and in 'definer!'.

'definer!' ( definer xt --  ) gforth-obsolete "definer!"
   The word represented by XT changes its behaviour to the behaviour
associated with DEFINER.

   'Code-address!', 'does-code!', and 'definer!' update the
'opt-compile,' method to a somewhat generic compiler for that word type
(in particular, primitives get the slow 'general-compile,' method rather
than the primitive-specific 'peephole-compile,').

6.31 Passing Commands to the Operating System
=============================================

Gforth allows you to pass an arbitrary string to the host operating
system shell (if such a thing exists) for execution.

'sh' ( "..." --  ) gforth-0.2 "sh"
   Execute the rest of the command line as shell command(s).
Afterwards, '$?' produces the exit status of the command.

'system' ( c-addr u --  ) gforth-0.2 "system"
   Pass the string specified by C-ADDR U to the host operating system
for execution in a sub-shell.  Afterwards, '$?' produces the exit status
of the command.  The value of the environment variable
'GFORTHSYSTEMPREFIX' (or its default value) is prepended to the string
(mainly to support using 'command.com' as shell in Windows instead of
whatever shell Cygwin uses by default; *note Environment variables::).

'sh-get' ( c-addr u -- c-addr2 u2  ) gforth-1.0 "sh-get"
   Run the shell command addr u; c-addr2 u2 is the output of the
command.  The exit code is in '$?', the output also in 'sh$ 2@'.

'$?' ( -- n  ) gforth-0.2 "dollar-question"
   'Value' -- the exit status returned by the most recently executed
'system' command.

'getenv' ( c-addr1 u1 -- c-addr2 u2 ) gforth-0.2 "getenv"
   The string c-addr1 u1 specifies an environment variable.  The string
c-addr2 u2 is the host operating system's expansion of that environment
variable.  If the environment variable does not exist, c-addr2 u2
specifies a string 0 characters in length.

6.32 Keeping track of Time
==========================

'ms' ( n --  ) facility-ext "ms"

'ns' ( d --  ) gforth-1.0 "ns"

'time&date' ( -- nsec nmin nhour nday nmonth nyear  ) facility-ext "time-and-date"
   Report the current time of day.  Seconds, minutes and hours are
numbered from 0.  Months are numbered from 1.

'>time&date&tz' ( udtime -- nsec nmin nhour nday nmonth nyear fdst ndstoff c-addrtz utz ) gforth-1.0 "to-time-and-date"
   Convert time in seconds since 1.1.1970 0:00Z to the current time of
day.  Seconds, minutes and hours are numbered from 0.  Months are
numbered from 1.

'utime' ( -- dtime ) gforth-0.5 "utime"
   Report the current time in microseconds since some epoch.  Use
'#1000000 um/mod nip' to convert to seconds

'ntime' ( -- dtime ) gforth-1.0 "ntime"
   Report the current time in nanoseconds since some epoch.

'cputime' ( -- duser dsystem ) gforth-0.5 "cputime"
   duser and dsystem are the respective user- and system-level CPU times
used since the start of the Forth system (excluding child processes), in
microseconds (the granularity may be much larger, however).  On
platforms without the getrusage call, it reports elapsed time (since
some epoch) for duser and 0 for dsystem.

6.33 Miscellaneous Words
========================

This section lists the Standard Forth words that are not documented
elsewhere in this manual.  Ultimately, they all need proper homes.

'quit' ( ?? -- ??  ) core "quit"
   Empty the return stack, make the user input device the input source,
enter interpret state and start the text interpreter.

   The following Standard Forth words are not currently supported by
Gforth (*note Standard conformance::):

   'EDITOR' 'EMIT?' 'FORGET'

7 Error messages
****************

A typical Gforth error message looks like this:

     in file included from \evaluated string/:-1
     in file included from ./yyy.fs:1
     ./xxx.fs:4: Invalid memory address
     >>>bar<<<
     Backtrace:
     $400E664C @
     $400E6664 foo

   The message identifying the error is 'Invalid memory address'.  The
error happened when text-interpreting line 4 of the file './xxx.fs'.
This line is given (it contains 'bar'), and the word on the line where
the error happened, is pointed out (with '>>>' and '<<<').

   The file containing the error was included in line 1 of './yyy.fs',
and 'yyy.fs' was included from a non-file (in this case, by giving
'yyy.fs' as command-line parameter to Gforth).

   At the end of the error message you find a return stack dump that can
be interpreted as a backtrace (possibly empty).  On top you find the top
of the return stack when the 'throw' happened, and at the bottom you
find the return stack entry just above the return stack of the topmost
text interpreter.

   To the right of most return stack entries you see a guess for the
word that pushed that return stack entry as its return address.  This
gives a backtrace.  In our case we see that 'bar' called 'foo', and
'foo' called '@' (and '@' had an _Invalid memory address_ exception).

   Note that the backtrace is not perfect: We don't know which return
stack entries are return addresses (so we may get false positives); and
in some cases (e.g., for 'abort"') we cannot determine from the return
address the word that pushed the return address, so for some return
addresses you see no names in the return stack dump.

   The return stack dump represents the return stack at the time when a
specific 'throw' was executed.  In programs that make use of 'catch', it
is not necessarily clear which 'throw' should be used for the return
stack dump (e.g., consider one 'throw' that indicates an error, which is
caught, and during recovery another error happens; which 'throw' should
be used for the stack dump?).  Gforth presents the return stack dump for
the first 'throw' after the last executed (not returned-to) 'catch' or
'nothrow'; this works well in the usual case.  To get the right
backtrace, you usually want to insert 'nothrow' or '['] false catch
2drop' after a 'catch' if the error is not rethrown.

   'Gforth' is able to do a return stack dump for throws generated from
primitives (e.g., invalid memory address, stack empty etc.);
'gforth-fast' is only able to do a return stack dump from a directly
called 'throw' (including 'abort' etc.).  Given an exception caused by a
primitive in 'gforth-fast', you will typically see no return stack dump
at all; however, if the exception is caught by 'catch' (e.g., for
restoring some state), and then 'throw'n again, the return stack dump
will be for the first such 'throw'.

   'gforth-fast' also does not attempt to differentiate between division
by zero and division overflow, because that costs time in every
division.

8 Tools
*******

See also *note Emacs and Gforth::.

8.1 'ans-report.fs': Report the words used, sorted by wordset
=============================================================

If you want to label a Forth program as Standard Program, you must
document which wordsets the program uses.

   The 'ans-report.fs' tool makes it easy for you to determine which
words from which wordset and which non-standard words your application
uses.  You simply have to include 'ans-report.fs' before loading the
program you want to check.  After loading your program, you can get the
report with 'print-ans-report'.  A typical use is to run this as batch
job like this:
     gforth ans-report.fs myprog.fs -e "print-ans-report bye"

   The output looks like this (for 'compat/control.fs'):
     The program uses the following words
     from CORE :
     : POSTPONE THEN ; immediate ?dup IF 0=
     from BLOCK-EXT :
     \
     from FILE :
     (

   'ans-report.fs' reports both Forth-94 and Forth-2012 wordsets.  For
words that are in both standards, it reports the wordset without suffix
(e.g., 'CORE-EXT').  For Forth-2012-only words, it reports the wordset
with a '-2012' suffix (e.g., 'CORE-EXT-2012'); and likewise for the
words that are Forth-94-only (i.e., that have been removed in
Forth-2012).

8.1.1 Caveats
-------------

Note that 'ans-report.fs' just checks which words are used, not whether
they are used in a standard-conforming way!

   Some words are defined in several wordsets in the standard.
'ans-report.fs' reports them for only one of the wordsets, and not
necessarily the one you expect.  It depends on usage which wordset is
the right one to specify.  E.g., if you only use the compilation
semantics of 'S"', it is a Core word; if you also use its interpretation
semantics, it is a File word.

8.2 Stack depth changes during interpretation
=============================================

Sometimes you notice that, after loading a file, there are items left on
the stack.  The tool 'depth-changes.fs' helps you find out quickly where
in the file these stack items are coming from.

   The simplest way of using 'depth-changes.fs' is to include it before
the file(s) you want to check, e.g.:

     gforth depth-changes.fs my-file.fs

   This will compare the stack depths of the data and FP stack at every
empty line (in interpretation state) against these depths at the last
empty line (in interpretation state).  If the depths are not equal, the
position in the file and the stack contents are printed with '~~' (*note
Debugging::).  This indicates that a stack depth change has occured in
the paragraph of non-empty lines before the indicated line.  It is a
good idea to leave an empty line at the end of the file, so the last
paragraph is checked, too.

   Checking only at empty lines usually works well, but sometimes you
have big blocks of non-empty lines (e.g., when building a big table),
and you want to know where in this block the stack depth changed.  You
can check all interpreted lines with

     gforth depth-changes.fs -e "' all-lines is depth-changes-filter" my-file.fs

   This checks the stack depth at every end-of-line.  So the depth
change occured in the line reported by the '~~' (not in the line
before).

   Note that, while this offers better accuracy in indicating where the
stack depth changes, it will often report many intentional stack depth
changes (e.g., when an interpreted computation stretches across several
lines).  You can suppress the checking of some lines by putting
backslashes at the end of these lines (not followed by white space), and
using

     gforth depth-changes.fs -e "' most-lines is depth-changes-filter" my-file.fs

9 Standard conformance
**********************

To the best of our knowledge, Gforth is a

   ANS Forth System and a Forth-2012 System
   * providing the Core Extensions word set
   * providing the Block word set
   * providing the Block Extensions word set
   * providing the Double-Number word set
   * providing the Double-Number Extensions word set
   * providing the Exception word set
   * providing the Exception Extensions word set
   * providing the Facility word set
   * providing the Facility Extensions word set, except 'EMIT?'
   * providing the File Access word set
   * providing the File Access Extensions word set
   * providing the Floating-Point word set
   * providing the Floating-Point Extensions word set
   * providing the Locals word set
   * providing the Locals Extensions word set
   * providing the Memory-Allocation word set
   * providing the Memory-Allocation Extensions word set
   * providing the Programming-Tools word set
   * providing the Programming-Tools Extensions word set, except
     'EDITOR' and 'FORGET'
   * providing the Search-Order word set
   * providing the Search-Order Extensions word set
   * providing the String word set
   * providing the String Extensions word set
   * providing the Extended-Character wordset

   Gforth has the following environmental restrictions:

   * While processing the OS command line, if an exception is not
     caught, Gforth exits with a non-zero exit code instead of
     performing QUIT.

   * When an 'throw' is performed after a 'query', Gforth does not
     always restore the input source specification in effect at the
     corresponding catch.

   In addition, Standard Forth systems are required to document certain
implementation choices.  This chapter tries to meet these requirements
for the Forth-94 standard.  For the Forth-2012 standard, we decided to
produce the additional documentation only if there is demand.  So if you
are really missing this documentation, please let us know.

   In many cases, the following documentation gives a way to ask the
system for the information instead of providing the information
directly, in particular, if the information depends on the processor,
the operating system or the installation options chosen, or if they are
likely to change during the maintenance of Gforth.

9.1 The Core Words
==================

9.1.1 Implementation Defined Options
------------------------------------

(Cell) aligned addresses:
     processor-dependent.  Gforth's alignment words perform natural
     alignment (e.g., an address aligned for a datum of size 8 is
     divisible by 8).  Unaligned accesses usually result in a '-23
     THROW'.

'EMIT' and non-graphic characters:
     The character is output using the C library function (actually,
     macro) 'putc'.

character editing of 'ACCEPT' and 'EXPECT':
     This is modeled on the GNU readline library (*note Command Line
     Editing: (readline)Readline Interaction.) with Emacs-like key
     bindings.  'Tab' deviates a little by producing a full word
     completion every time you type it (instead of producing the common
     prefix of all completions).  *Note Command-line editing::.

character set:
     The character set of your computer and display device.  Gforth is
     8-bit-clean (but some other component in your system may make
     trouble).

Character-aligned address requirements:
     installation-dependent.  Currently a character is represented by a
     C 'unsigned char'; in the future we might switch to 'wchar_t'
     (Comments on that requested).

character-set extensions and matching of names:
     Any character except the ASCII NUL character can be used in a name.
     Matching is case-insensitive (except in 'TABLE's).  The matching is
     performed using the C library function 'strncasecmp', whose
     function is probably influenced by the locale.  E.g., the 'C'
     locale does not know about accents and umlauts, so they are matched
     case-sensitively in that locale.  For portability reasons it is
     best to write programs such that they work in the 'C' locale.  Then
     one can use libraries written by a Polish programmer (who might use
     words containing ISO Latin-2 encoded characters) and by a French
     programmer (ISO Latin-1) in the same program (of course, 'WORDS'
     will produce funny results for some of the words (which ones,
     depends on the font you are using)).  Also, the locale you prefer
     may not be available in other operating systems.  Hopefully,
     Unicode will solve these problems one day.

conditions under which control characters match a space delimiter:
     If 'word' is called with the space character as a delimiter, all
     white-space characters (as identified by the C macro 'isspace()')
     are delimiters.  'Parse', on the other hand, treats space like
     other delimiters.  'Parse-name', which is used by the outer
     interpreter (aka text interpreter) by default, treats all
     white-space characters as delimiters.

format of the control-flow stack:
     The data stack is used as control-flow stack.  The size of a
     control-flow stack item in cells is given by the constant
     'cs-item-size'.  At the time of this writing, an item consists of a
     (pointer to a) locals list (third), an address in the code
     (second), and a tag for identifying the item (TOS). The following
     tags are used: 'defstart', 'live-orig', 'dead-orig', 'dest',
     'do-dest', 'scopestart'.

conversion of digits > 35
     The characters '[\]^_'' are the digits with the decimal value
     36-41.  There is no way to input many of the larger digits.

display after input terminates in 'ACCEPT' and 'EXPECT':
     The cursor is moved to the end of the entered string.  If the input
     is terminated using the 'Return' key, a space is typed.

exception abort sequence of 'ABORT"':
     The error string is stored into the variable '"error' and a '-2
     throw' is performed.

input line terminator:
     For interactive input, 'C-m' (CR) and 'C-j' (LF) terminate lines.
     One of these characters is typically produced when you type the
     'Enter' or 'Return' key.

maximum size of a counted string:
     's" /counted-string" environment? drop .'.  Currently 255
     characters on all platforms, but this may change.

maximum size of a parsed string:
     Given by the constant '/line'.  Currently 255 characters.

maximum size of a definition name, in characters:
     MAXU/8

maximum string length for 'ENVIRONMENT?', in characters:
     MAXU/8

method of selecting the user input device:
     The user input device is the standard input.  There is currently no
     way to change it from within Gforth.  However, the input can
     typically be redirected in the command line that starts Gforth.

method of selecting the user output device:
     'EMIT' and 'TYPE' output to the file-id stored in the value
     'outfile-id' ('stdout' by default).  Gforth uses unbuffered output
     when the user output device is a terminal, otherwise the output is
     buffered.

methods of dictionary compilation:
     What are we expected to document here?

number of bits in one address unit:
     's" address-units-bits" environment? drop .'.  8 in all current
     platforms.

number representation and arithmetic:
     Processor-dependent.  Binary two's complement on all current
     platforms.

ranges for integer types:
     Installation-dependent.  Make environmental queries for 'MAX-N',
     'MAX-U', 'MAX-D' and 'MAX-UD'.  The lower bounds for unsigned (and
     positive) types is 0.  The lower bound for signed types on two's
     complement and one's complement machines machines can be computed
     by adding 1 to the upper bound.

read-only data space regions:
     The whole Forth data space is writable.

size of buffer at 'WORD':
     'PAD HERE - .'.  104 characters on 32-bit machines.  The buffer is
     shared with the pictured numeric output string.  If overwriting
     'PAD' is acceptable, it is as large as the remaining dictionary
     space, although only as much can be sensibly used as fits in a
     counted string.

size of one cell in address units:
     '1 cells .'.

size of one character in address units:
     '1 chars .'.  1 on all current platforms.

size of the keyboard terminal buffer:
     Varies.  You can determine the size at a specific time using 'lp@
     tib - .'.  It is shared with the locals stack and TIBs of files
     that include the current file.  You can change the amount of space
     for TIBs and locals stack at Gforth startup with the command line
     option '-l'.

size of the pictured numeric output buffer:
     'PAD HERE - .'.  104 characters on 32-bit machines.  The buffer is
     shared with 'WORD'.

size of the scratch area returned by 'PAD':
     The remainder of dictionary space.  'unused pad here - - .'.

system case-sensitivity characteristics:
     Dictionary searches are case-insensitive (except in 'TABLE's).
     However, as explained above under character-set extensions, the
     matching for non-ASCII characters is determined by the locale you
     are using.  In the default 'C' locale all non-ASCII characters are
     matched case-sensitively.

system prompt:
     ' ok' in interpret state, ' compiled' in compile state.

division rounding:
     The ordinary division words '/ mod /mod */ */mod' perform floored
     division (with the default installation of Gforth).  You can check
     this with 's" floored" environment? drop .'.  If you write programs
     that need a specific division rounding, best use 'fm/mod' or
     'sm/rem' for portability.

values of 'STATE' when true:
     -1.

values returned after arithmetic overflow:
     On two's complement machines, arithmetic is performed modulo
     2**bits-per-cell for single arithmetic and 4**bits-per-cell for
     double arithmetic (with appropriate mapping for signed types).
     Division by zero typically results in a '-55 throw' (Floating-point
     unidentified fault) or '-10 throw' (divide by zero).  Integer
     division overflow can result in these throws, or in '-11 throw'; in
     'gforth-fast' division overflow and divide by zero may also result
     in returning bogus results without producing an exception.

whether the current definition can be found after DOES>:
     No.

9.1.2 Ambiguous conditions
--------------------------

a name is neither a word nor a number:
     '-13 throw' (Undefined word).

a definition name exceeds the maximum length allowed:
     '-19 throw' (Word name too long)

addressing a region not inside the various data spaces of the forth system:
     The stacks, code space and header space are accessible.  Machine
     code space is typically readable.  Accessing other addresses gives
     results dependent on the operating system.  On decent systems: '-9
     throw' (Invalid memory address).

argument type incompatible with parameter:
     This is usually not caught.  Some words perform checks, e.g., the
     control flow words, and issue a 'ABORT"' or '-12 THROW' (Argument
     type mismatch).

attempting to obtain the execution token of a word with undefined execution semantics:
     The execution token represents the interpretation semantics of the
     word.  Gforth defines interpretation semantics for all words; for
     words where the standard does not define interpretation semantics,
     but defines the execution semantics (except 'LEAVE'), the
     interpretation semantics are to perform the execution semantics.
     For words where the standard defines no interprtation semantics,
     but defined compilation semantics (plus 'LEAVE'), the
     interpretation semantics are to perform the compilation semantics.
     Some words are marked as compile-only, and ''' gives a warning for
     these words.

dividing by zero:
     On some platforms, this produces a '-10 throw' (Division by zero);
     on other systems, this typically results in a '-55 throw'
     (Floating-point unidentified fault).

insufficient data stack or return stack space:
     Depending on the operating system, the installation, and the
     invocation of Gforth, this is either checked by the memory
     management hardware, or it is not checked.  If it is checked, you
     typically get a '-3 throw' (Stack overflow), '-5 throw' (Return
     stack overflow), or '-9 throw' (Invalid memory address) (depending
     on the platform and how you achieved the overflow) as soon as the
     overflow happens.  If it is not checked, overflows typically result
     in mysterious illegal memory accesses, producing '-9 throw'
     (Invalid memory address) or '-23 throw' (Address alignment
     exception); they might also destroy the internal data structure of
     'ALLOCATE' and friends, resulting in various errors in these words.

insufficient space for loop control parameters:
     Like other return stack overflows.

insufficient space in the dictionary:
     If you try to allot (either directly with 'allot', or indirectly
     with ',', 'create' etc.)  more memory than available in the
     dictionary, you get a '-8 throw' (Dictionary overflow).  If you try
     to access memory beyond the end of the dictionary, the results are
     similar to stack overflows.

interpreting a word with undefined interpretation semantics:
     Gforth defines interpretation semantics for all words; for words
     where the standard defines execution semantics (except 'LEAVE'),
     the interpretation semantics are to perform the execution
     semantics.  For words where the standard defines no interprtation
     semantics, but defined compilation semantics (plus 'LEAVE'), the
     interpretation semantics are to perform the compilation semantics.
     Some words are marked as compile-only, and text-interpreting them
     gives a warning.

modifying the contents of the input buffer or a string literal:
     These are located in writable memory and can be modified.

overflow of the pictured numeric output string:
     '-17 throw' (Pictured numeric ouput string overflow).

parsed string overflow:
     'PARSE' cannot overflow.  'WORD' does not check for overflow.

producing a result out of range:
     On two's complement machines, arithmetic is performed modulo
     2**bits-per-cell for single arithmetic and 4**bits-per-cell for
     double arithmetic (with appropriate mapping for signed types).
     Division by zero typically results in a '-10 throw' (divide by
     zero) or '-55 throw' (floating point unidentified fault).  Overflow
     on division may result in these errors or in '-11 throw' (result
     out of range).  'Gforth-fast' may silently produce bogus results on
     division overflow or division by zero.  'Convert' and '>number'
     currently overflow silently.

reading from an empty data or return stack:
     The data stack is checked by the outer (aka text) interpreter after
     every word executed.  If it has underflowed, a '-4 throw' (Stack
     underflow) is performed.  Apart from that, stacks may be checked or
     not, depending on operating system, installation, and invocation.
     If they are caught by a check, they typically result in '-4 throw'
     (Stack underflow), '-6 throw' (Return stack underflow) or '-9
     throw' (Invalid memory address), depending on the platform and
     which stack underflows and by how much.  Note that even if the
     system uses checking (through the MMU), your program may have to
     underflow by a significant number of stack items to trigger the
     reaction (the reason for this is that the MMU, and therefore the
     checking, works with a page-size granularity).  If there is no
     checking, the symptoms resulting from an underflow are similar to
     those from an overflow.  Unbalanced return stack errors can result
     in a variety of symptoms, including '-9 throw' (Invalid memory
     address) and Illegal Instruction (typically '-260 throw').

unexpected end of the input buffer, resulting in an attempt to use a zero-length string as a name:
     'Create' and its descendants perform a '-16 throw' (Attempt to use
     zero-length string as a name).  Words like ''' probably will not
     find what they search.  Note that it is possible to create
     zero-length names with 'nextname' (should it not?).

'>IN' greater than input buffer:
     The next invocation of a parsing word returns a string with length
     0.

'RECURSE' appears after 'DOES>':
     Compiles a recursive call to the code after 'DOES>'.

argument input source different than current input source for 'RESTORE-INPUT':
     '-12 THROW'.  Note that, once an input file is closed (e.g.,
     because the end of the file was reached), its source-id may be
     reused.  Therefore, restoring an input source specification
     referencing a closed file may lead to unpredictable results instead
     of a '-12 THROW'.

     In the future, Gforth may be able to restore input source
     specifications from other than the current input source.

data space containing definitions gets de-allocated:
     Deallocation with 'allot' is not checked.  This typically results
     in memory access faults or execution of illegal instructions.

data space read/write with incorrect alignment:
     Processor-dependent.  Typically results in a '-23 throw' (Address
     alignment exception).  Under Linux-Intel on a 486 or later
     processor with alignment turned on, incorrect alignment results in
     a '-9 throw' (Invalid memory address).  There are reportedly some
     processors with alignment restrictions that do not report
     violations.

data space pointer not properly aligned, ',', 'C,':
     Like other alignment errors.

less than u+2 stack items ('PICK' and 'ROLL'):
     Like other stack underflows.

loop control parameters not available:
     Not checked.  The counted loop words simply assume that the top of
     return stack items are loop control parameters and behave
     accordingly.

most recent definition does not have a name ('IMMEDIATE'):
     'abort" last word was headerless"'.

name not defined by 'VALUE' used by 'TO':
     '-32 throw' (Invalid name argument) (unless name is a local or was
     defined by 'CONSTANT'; in the latter case it just changes the
     constant).

name not found (''', 'POSTPONE', '[']', '[COMPILE]'):
     '-13 throw' (Undefined word)

parameters are not of the same type ('DO', '?DO', 'WITHIN'):
     Gforth behaves as if they were of the same type.  I.e., you can
     predict the behaviour by interpreting all parameters as, e.g.,
     signed.

'POSTPONE' or '[COMPILE]' applied to 'TO':
     Assume ': X POSTPONE TO ; IMMEDIATE'.  'X' performs the compilation
     semantics of 'TO'.

String longer than a counted string returned by 'WORD':
     Not checked.  The string will be ok, but the count will, of course,
     contain only the least significant bits of the length.

u greater than or equal to the number of bits in a cell ('LSHIFT', 'RSHIFT'):
     Processor-dependent.  Typical behaviours are returning 0 and using
     only the low bits of the shift count.

word not defined via 'CREATE':
     '>BODY' produces the PFA of the word no matter how it was defined.

     'DOES>' changes the execution semantics of the last defined word no
     matter how it was defined.  E.g., 'CONSTANT DOES>' is equivalent to
     'CREATE , DOES>'.

words improperly used outside '<#' and '#>':
     Not checked.  As usual, you can expect memory faults.

9.1.3 Other system documentation
--------------------------------

nonstandard words using 'PAD':
     None.

operator's terminal facilities available:
     After processing the OS's command line, Gforth goes into
     interactive mode, and you can give commands to Gforth
     interactively.  The actual facilities available depend on how you
     invoke Gforth.

program data space available:
     'UNUSED .' gives the remaining dictionary space.  The total
     dictionary space can be specified with the '-m' switch (*note
     Invoking Gforth::) when Gforth starts up.

return stack space available:
     You can compute the total return stack space in cells with 's"
     RETURN-STACK-CELLS" environment? drop .'.  You can specify it at
     startup time with the '-r' switch (*note Invoking Gforth::).

stack space available:
     You can compute the total data stack space in cells with 's"
     STACK-CELLS" environment? drop .'.  You can specify it at startup
     time with the '-d' switch (*note Invoking Gforth::).

system dictionary space required, in address units:
     Type 'here forthstart - .' after startup.  At the time of this
     writing, this gives 80080 (bytes) on a 32-bit system.

9.2 The optional Block word set
===============================

9.2.1 Implementation Defined Options
------------------------------------

the format for display by 'LIST':
     First the screen number is displayed, then 16 lines of 64
     characters, each line preceded by the line number.

the length of a line affected by '\':
     64 characters.

9.2.2 Ambiguous conditions
--------------------------

correct block read was not possible:
     Typically results in a 'throw' of some OS-derived value (between
     -512 and -2048).  If the blocks file was just not long enough,
     blanks are supplied for the missing portion.

I/O exception in block transfer:
     Typically results in a 'throw' of some OS-derived value (between
     -512 and -2048).

invalid block number:
     '-35 throw' (Invalid block number)

a program directly alters the contents of 'BLK':
     The input stream is switched to that other block, at the same
     position.  If the storing to 'BLK' happens when interpreting
     non-block input, the system will get quite confused when the block
     ends.

no current block buffer for 'UPDATE':
     'UPDATE' has no effect.

9.2.3 Other system documentation
--------------------------------

any restrictions a multiprogramming system places on the use of buffer addresses:
     No restrictions (yet).

the number of blocks available for source and data:
     depends on your disk space.

9.3 The optional Double Number word set
=======================================

9.3.1 Ambiguous conditions
--------------------------

d outside of range of n in 'D>S':
     The least significant cell of d is produced.

9.4 The optional Exception word set
===================================

9.4.1 Implementation Defined Options
------------------------------------

'THROW'-codes used in the system:
     The codes -256--511 are used for reporting signals.  The mapping
     from OS signal numbers to throw codes is -256-signal.  The codes
     -512--2047 are used for OS errors (for file and memory allocation
     operations).  The mapping from OS error numbers to throw codes is
     -512-'errno'.  One side effect of this mapping is that undefined OS
     errors produce a message with a strange number; e.g., '-1000 THROW'
     results in 'Unknown error 488' on my system.

9.5 The optional Facility word set
==================================

9.5.1 Implementation Defined Options
------------------------------------

encoding of keyboard events ('EKEY'):
     Keys corresponding to ASCII characters are encoded as ASCII
     characters.  Other keys are encoded with the constants 'k-left',
     'k-right', 'k-up', 'k-down', 'k-home', 'k-end', 'k1', 'k2', 'k3',
     'k4', 'k5', 'k6', 'k7', 'k8', 'k9', 'k10', 'k11', 'k12', 'k-winch',
     'k-eof'.

duration of a system clock tick:
     System dependent.  With respect to 'MS', the time is specified in
     microseconds.  How well the OS and the hardware implement this, is
     another question.

repeatability to be expected from the execution of 'MS':
     System dependent.  On Unix, a lot depends on load.  If the system
     is lightly loaded, and the delay is short enough that Gforth does
     not get swapped out, the performance should be acceptable.  Under
     MS-DOS and other single-tasking systems, it should be good.

9.5.2 Ambiguous conditions
--------------------------

'AT-XY' can't be performed on user output device:
     Largely terminal dependent.  No range checks are done on the
     arguments.  No errors are reported.  You may see some garbage
     appearing, you may see simply nothing happen.

9.6 The optional File-Access word set
=====================================

9.6.1 Implementation Defined Options
------------------------------------

file access methods used:
     'R/O', 'R/W' and 'BIN' work as you would expect.  'W/O' translates
     into the C file opening mode 'w' (or 'wb'): The file is cleared, if
     it exists, and created, if it does not (with both 'open-file' and
     'create-file').  Under Unix 'create-file' creates a file with 666
     permissions modified by your umask.

file exceptions:
     The file words do not raise exceptions (except, perhaps, memory
     access faults when you pass illegal addresses or file-ids).

file line terminator:
     System-dependent.  Gforth uses C's newline character as line
     terminator.  What the actual character code(s) of this are is
     system-dependent.

file name format:
     System dependent.  Gforth just uses the file name format of your
     OS.

information returned by 'FILE-STATUS':
     'FILE-STATUS' returns the most powerful file access mode allowed
     for the file: Either 'R/O', 'W/O' or 'R/W'.  If the file cannot be
     accessed, 'R/O BIN' is returned.  'BIN' is applicable along with
     the returned mode.

input file state after an exception when including source:
     All files that are left via the exception are closed.

ior values and meaning:
     The iors returned by the file and memory allocation words are
     intended as throw codes.  They typically are in the range
     -512--2047 of OS errors.  The mapping from OS error numbers to iors
     is -512-errno.

maximum depth of file input nesting:
     limited by the amount of return stack, locals/TIB stack, and the
     number of open files available.  This should not give you troubles.

maximum size of input line:
     '/line'.  Currently 255.

methods of mapping block ranges to files:
     By default, blocks are accessed in the file 'blocks.fb' in the
     current working directory.  The file can be switched with 'USE'.

number of string buffers provided by 'S"':
     As many as memory available; the strings are stored in memory
     blocks allocated with ALLOCATE indefinitely.

size of string buffer used by 'S"':
     '/line'.  currently 255.

9.6.2 Ambiguous conditions
--------------------------

attempting to position a file outside its boundaries:
     'REPOSITION-FILE' is performed as usual: Afterwards,
     'FILE-POSITION' returns the value given to 'REPOSITION-FILE'.

attempting to read from file positions not yet written:
     End-of-file, i.e., zero characters are read and no error is
     reported.

file-id is invalid ('INCLUDE-FILE'):
     An appropriate exception may be thrown, but a memory fault or other
     problem is more probable.

I/O exception reading or closing file-id ('INCLUDE-FILE', 'INCLUDED'):
     The ior produced by the operation, that discovered the problem, is
     thrown.

named file cannot be opened ('INCLUDED'):
     The ior produced by 'open-file' is thrown.

requesting an unmapped block number:
     There are no unmapped legal block numbers.  On some operating
     systems, writing a block with a large number may overflow the file
     system and have an error message as consequence.

using 'source-id' when 'blk' is non-zero:
     'source-id' performs its function.  Typically it will give the id
     of the source which loaded the block.  (Better ideas?)

9.7 The optional Floating-Point word set
========================================

9.7.1 Implementation Defined Options
------------------------------------

format and range of floating point numbers:
     System-dependent; the 'double' type of C.

results of 'REPRESENT' when float is out of range:
     System dependent; 'REPRESENT' is implemented using the C library
     function 'ecvt()' and inherits its behaviour in this respect.

rounding or truncation of floating-point numbers:
     System dependent; the rounding behaviour is inherited from the
     hosting C compiler.  IEEE-FP-based (i.e., most) systems by default
     round to nearest, and break ties by rounding to even (i.e., such
     that the last bit of the mantissa is 0).

size of floating-point stack:
     's" FLOATING-STACK" environment? drop .' gives the total size of
     the floating-point stack (in floats).  You can specify this on
     startup with the command-line option '-f' (*note Invoking
     Gforth::).

width of floating-point stack:
     '1 floats'.

9.7.2 Ambiguous conditions
--------------------------

'df@' or 'df!' used with an address that is not double-float aligned:
     System-dependent.  Typically results in a '-23 THROW' like other
     alignment violations.

'f@' or 'f!' used with an address that is not float aligned:
     System-dependent.  Typically results in a '-23 THROW' like other
     alignment violations.

floating-point result out of range:
     System-dependent.  Can result in a '-43 throw' (floating point
     overflow), '-54 throw' (floating point underflow), '-41 throw'
     (floating point inexact result), '-55 THROW' (Floating-point
     unidentified fault), or can produce a special value representing,
     e.g., Infinity.

'sf@' or 'sf!' used with an address that is not single-float aligned:
     System-dependent.  Typically results in an alignment fault like
     other alignment violations.

'base' is not decimal ('REPRESENT', 'F.', 'FE.', 'FS.'):
     The floating-point number is converted into decimal nonetheless.

Both arguments are equal to zero ('FATAN2'):
     System-dependent.  'FATAN2' is implemented using the C library
     function 'atan2()'.

Using 'FTAN' on an argument r1 where cos(r1) is zero:
     System-dependent.  Anyway, typically the cos of r1 will not be zero
     because of small errors and the tan will be a very large (or very
     small) but finite number.

d cannot be presented precisely as a float in 'D>F':
     The result is rounded to the nearest float.

dividing by zero:
     Platform-dependent; can produce an Infinity, NaN, '-42 throw'
     (floating point divide by zero) or '-55 throw' (Floating-point
     unidentified fault).

exponent too big for conversion ('DF!', 'DF@', 'SF!', 'SF@'):
     System dependent.  On IEEE-FP based systems the number is converted
     into an infinity.

float<1 ('FACOSH'):
     Platform-dependent; on IEEE-FP systems typically produces a NaN.

float<=-1 ('FLNP1'):
     Platform-dependent; on IEEE-FP systems typically produces a NaN (or
     a negative infinity for float=-1).

float<=0 ('FLN', 'FLOG'):
     Platform-dependent; on IEEE-FP systems typically produces a NaN (or
     a negative infinity for float=0).

float<0 ('FASINH', 'FSQRT'):
     Platform-dependent; for 'fsqrt' this typically gives a NaN, for
     'fasinh' some platforms produce a NaN, others a number (bug in the
     C library?).

|float|>1 ('FACOS', 'FASIN', 'FATANH'):
     Platform-dependent; IEEE-FP systems typically produce a NaN.

integer part of float cannot be represented by d in 'F>D':
     Platform-dependent; typically, some double number is produced and
     no error is reported.

string larger than pictured numeric output area ('f.', 'fe.', 'fs.'):
     'Precision' characters of the numeric output area are used.  If
     'precision' is too high, these words will smash the data or code
     close to 'here'.

9.8 The optional Locals word set
================================

9.8.1 Implementation Defined Options
------------------------------------

maximum number of locals in a definition:
     's" #locals" environment? drop .'.  Currently 15.  This is a lower
     bound, e.g., on a 32-bit machine there can be 41 locals of up to 8
     characters.  The number of locals in a definition is bounded by the
     size of locals-buffer, which contains the names of the locals.

9.8.2 Ambiguous conditions
--------------------------

executing a named local in interpretation state:
     Compiles the local into the current definition (just as in compile
     state); in addition text-interpreting a local in interpretation
     state gives an "is compile-only" warning.

name not defined by 'VALUE' or '(LOCAL)' ('TO'):
     '-32 throw' (Invalid name argument)

9.9 The optional Memory-Allocation word set
===========================================

9.9.1 Implementation Defined Options
------------------------------------

values and meaning of ior:
     The iors returned by the file and memory allocation words are
     intended as throw codes.  They typically are in the range
     -512--2047 of OS errors.  The mapping from OS error numbers to iors
     is -512-errno.

9.10 The optional Programming-Tools word set
============================================

9.10.1 Implementation Defined Options
-------------------------------------

ending sequence for input following ';CODE' and 'CODE':
     'END-CODE'

manner of processing input following ';CODE' and 'CODE':
     The 'ASSEMBLER' vocabulary is pushed on the search order stack, and
     the input is processed by the text interpreter, (starting) in
     interpret state.

search order capability for 'EDITOR' and 'ASSEMBLER':
     The Search-Order word set.

source and format of display by 'SEE':
     The source for 'see' is the executable code used by the inner
     interpreter.  The current 'see' tries to output Forth source code
     (and on some platforms, assembly code for primitives) as well as
     possible.

9.10.2 Ambiguous conditions
---------------------------

deleting the compilation word list ('FORGET'):
     Not implemented (yet).

fewer than u+1 items on the control-flow stack ('CS-PICK', 'CS-ROLL'):
     This typically results in an 'abort"' with a descriptive error
     message (may change into a '-22 throw' (Control structure mismatch)
     in the future).  You may also get a memory access error.  If you
     are unlucky, this ambiguous condition is not caught.

name can't be found ('FORGET'):
     Not implemented (yet).

name not defined via 'CREATE':
     ';CODE' behaves like 'DOES>' in this respect, i.e., it changes the
     execution semantics of the last defined word no matter how it was
     defined.

'POSTPONE' applied to '[IF]':
     After defining ': X POSTPONE [IF] ; IMMEDIATE'.  'X' is equivalent
     to '[IF]'.

reaching the end of the input source before matching '[ELSE]' or '[THEN]':
     Continue in the same state of conditional compilation in the next
     outer input source.  Currently there is no warning to the user
     about this.

removing a needed definition ('FORGET'):
     Not implemented (yet).

9.11 The optional Search-Order word set
=======================================

9.11.1 Implementation Defined Options
-------------------------------------

maximum number of word lists in search order:
     's" wordlists" environment? drop .'.  Currently 16.

minimum search order:
     'root root'.

9.11.2 Ambiguous conditions
---------------------------

changing the compilation word list (during compilation):
     The word is entered into the word list that was the compilation
     word list at the start of the definition.  Any changes to the name
     field (e.g., 'immediate') or the code field (e.g., when executing
     'DOES>') are applied to the latest defined word (as reported by
     'latest' or 'latestxt'), if possible, irrespective of the
     compilation word list.

search order empty ('previous'):
     'abort" Vocstack empty"'.

too many word lists in search order ('also'):
     'abort" Vocstack full"'.

10 Should I use Gforth extensions?
**********************************

As you read through the rest of this manual, you will see documentation
for Standard words, and documentation for some appealing Gforth
extensions.  You might ask yourself the question: "Should I restrict
myself to the standard, or should I use the extensions?"

   The answer depends on the goals you have for the program you are
working on:

   * Is it just for yourself or do you want to share it with others?

   * If you want to share it, do the others all use Gforth?

   * If it is just for yourself, do you want to restrict yourself to
     Gforth?

   If restricting the program to Gforth is ok, then there is no reason
not to use extensions.  It is still a good idea to keep to the standard
where it is easy, in case you want to reuse these parts in another
program that you want to be portable.

   If you want to be able to port the program to other Forth systems,
there are the following points to consider:

   * Most Forth systems that are being maintained support Standard
     Forth.  So if your program complies with the standard, it will be
     portable among many systems.

   * A number of the Gforth extensions can be implemented in Standard
     Forth using public-domain files provided in the 'compat/'
     directory.  These are mentioned in the text in passing.  There is
     no reason not to use these extensions, your program will still be
     Standard Forth compliant; just include the appropriate compat files
     with your program.

   * The tool 'ans-report.fs' (*note Standard Report::) makes it easy to
     analyse your program and determine what non-Standard words it
     relies upon.  However, it does not check whether you use standard
     words in a non-standard way.

   * Some techniques are not standardized by Standard Forth, and are
     hard or impossible to implement in a standard way, but can be
     implemented in most Forth systems easily, and usually in similar
     ways (e.g., accessing word headers).  Forth has a rich historical
     precedent for programmers taking advantage of
     implementation-dependent features of their tools (for example,
     relying on a knowledge of the dictionary structure).  Sometimes
     these techniques are necessary to extract every last bit of
     performance from the hardware, sometimes they are just a
     programming shorthand.

   * Does using a Gforth extension save more work than the porting this
     part to other Forth systems (if any) will cost?

   * Is the additional functionality worth the reduction in portability
     and the additional porting problems?

   In order to perform these considerations, you need to know what's
standard and what's not.  This manual generally states if something is
non-standard, but the authoritative source is the standard document
(https://forth-standard.org/standard/words).  Appendix A of the Standard
(RATIONALE) provides a valuable insight into the thought processes of
the technical committee.

   Note also that portability between Forth systems is not the only
portability issue; there is also the issue of portability between
different platforms (processor/OS combinations).

11 Model
********

This chapter has yet to be written.  It will contain information, on
which internal structures you can rely.

12 Integrating Gforth into C programs
*************************************

Several people like to use Forth as scripting language for applications
that are otherwise written in C, C++, or some other language.

   The Forth system ATLAST provides facilities for embedding it into
applications; unfortunately it has several disadvantages: most
importantly, it is not based on Standard Forth, and it is apparently
dead (i.e., not developed further and not supported).  The facilities
provided by Gforth in this area are inspired by ATLAST's facilities, so
making the switch should not be hard.

   We also tried to design the interface such that it can easily be
implemented by other Forth systems, so that we may one day arrive at a
standardized interface.  Such a standard interface would allow you to
replace the Forth system without having to rewrite C code.

   You embed the Gforth interpreter by linking with the library
'libgforth.a' or 'libgforth.so' (give the compiler the option
'-lgforth', or for one of the other engines '-lgforth-fast',
'-lgforth-itc', or '-lgforth-ditc').  All global symbols in this library
that belong to the interface, have the prefix 'gforth_'; if a common
interface emerges, the functions may also be available through
'#define's with the prefix 'forth_'.

   You can include the declarations of Forth types, the functions and
variables of the interface with '#include <gforth.h>'.

   You can now run a Gforth session by either calling 'gforth_main' or
using the components:

     Cell gforth_main(int argc, char **argv, char **env)
     {
       Cell retvalue=gforth_start(argc, argv);

       if(retvalue == -56) { /* throw-code for quit */
         retvalue = gforth_bootmessage();     // show boot message
         if(retvalue == -56)
           retvalue = gforth_quit(); // run quit loop
       }
       gforth_cleanup();
       gforth_printmetrics();
       // gforth_free_dict(); // if you want to restart, do this

       return retvalue;
     }

   To interact with the Forth interpreter, there's 'Xt gforth_find(Char
* name)' and 'Cell gforth_execute(Xt xt)'.

   More documentation needs to be put here.

12.1 Types
==========

'Cell', 'UCell': data stack elements.

   'Float': float stack element.

   'Address', 'Xt', 'Label': pointer typies to memory, Forth words, and
Forth instructions inside the VM.

12.2 Variables
==============

Data and FP Stack pointer.  Area sizes.  Accessing the Stacks

   'gforth_SP', 'gforth_FP'.

12.3 Functions
==============

     void *gforth_engine(Xt *, stackpointers *);
     Cell gforth_main(int argc, char **argv, char **env);
     int gforth_args(int argc, char **argv, char **path, char **imagename);
     ImageHeader* gforth_loader(char* imagename, char* path);
     user_area* gforth_stacks(Cell dsize, Cell rsize, Cell fsize, Cell lsize);
     void gforth_free_stacks(user_area* t);
     void gforth_setstacks(user_area * t);
     void gforth_free_dict();
     Cell gforth_go(Xt* ip0);
     Cell gforth_boot(int argc, char** argv, char* path);
     void gforth_bootmessage();
     Cell gforth_start(int argc, char ** argv);
     Cell gforth_quit();
     Xt gforth_find(Char * name);
     Cell gforth_execute(Xt xt);
     void gforth_cleanup();
     void gforth_printmetrics();
     void gforth_setwinch();

12.4 Signals
============

Gforth sets up signal handlers to catch exceptions and window size
changes.  This may interfere with your C program.

13 Emacs and Gforth
*******************

Gforth comes with 'gforth.el', an improved version of 'forth.el' by
Goran Rydqvist (included in the TILE package).  The improvements are:

   * A better handling of indentation.
   * A custom hilighting engine for Forth-code.
   * Comment paragraph filling ('M-q')
   * Commenting ('C-x \') and uncommenting ('C-u C-x \') of regions
   * Removal of debugging tracers ('C-x ~', *note Debugging::).
   * Support of the 'info-lookup' feature for looking up the
     documentation of a word.
   * Support for reading and writing blocks files.

   To get a basic description of these features, enter Forth mode and
type 'C-h m'.

   In addition, Gforth supports Emacs quite well: The source code
locations given in error messages, debugging output (from '~~') and
failed assertion messages are in the right format for Emacs' compilation
mode (*note Running Compilations under Emacs: (emacs)Compilation.) so
the source location corresponding to an error or other message is only a
few keystrokes away ('C-x `' for the next error, 'C-c C-c' for the error
under the cursor).

   Moreover, for words documented in this manual, you can look up the
glossary entry quickly by using 'C-h TAB' ('info-lookup-symbol', *note
Documentation Commands: (emacs)Documentation.).  This feature requires
Emacs 20.3 or later and does not work for words containing ':'.

13.1 Installing gforth.el
=========================

To make the features from 'gforth.el' available in Emacs, add the
following lines to your '.emacs' file:

     (autoload 'forth-mode "gforth.el")
     (setq auto-mode-alist (cons '("\\.fs\\'" . forth-mode)
     			    auto-mode-alist))
     (autoload 'forth-block-mode "gforth.el")
     (setq auto-mode-alist (cons '("\\.fb\\'" . forth-block-mode)
     			    auto-mode-alist))
     (add-hook 'forth-mode-hook (function (lambda ()
        ;; customize variables here:
        (setq forth-indent-level 4)
        (setq forth-minor-indent-level 2)
        (setq forth-hilight-level 3)
        ;;; ...
     )))

13.2 Emacs Tags
===============

If you 'require' 'etags.fs', a new 'TAGS' file will be produced (*note
Tags Tables: (emacs)Tags.) that contains the definitions of all words
defined afterwards.  You can then find the source for a word using
'M-.'.  Note that Emacs can use several tags files at the same time
(e.g., one for the Gforth sources and one for your program, *note
Selecting a Tags Table: (emacs)Select Tags Table.).  The TAGS file for
the preloaded words is '$(datadir)/gforth/$(VERSION)/TAGS' (e.g.,
'/usr/local/share/gforth/0.2.0/TAGS').  To get the best behaviour with
'etags.fs', you should avoid putting definitions both before and after
'require' etc., otherwise you will see the same file visited several
times by commands like 'tags-search'.

13.3 Hilighting
===============

'gforth.el' comes with a custom source hilighting engine.  When you open
a file in 'forth-mode', it will be completely parsed, assigning faces to
keywords, comments, strings etc.  While you edit the file, modified
regions get parsed and updated on-the-fly.

   Use the variable 'forth-hilight-level' to change the level of
decoration from 0 (no hilighting at all) to 3 (the default).  Even if
you set the hilighting level to 0, the parser will still work in the
background, collecting information about whether regions of text are
"compiled" or "interpreted".  Those information are required for
auto-indentation to work properly.  Set 'forth-disable-parser' to
non-nil if your computer is too slow to handle parsing.  This will have
an impact on the smartness of the auto-indentation engine, though.

   Sometimes Forth sources define new features that should be hilighted,
new control structures, defining-words etc.  You can use the variable
'forth-custom-words' to make 'forth-mode' hilight additional words and
constructs.  See the docstring of 'forth-words' for details (in Emacs,
type 'C-h v forth-words').

   'forth-custom-words' is meant to be customized in your '.emacs' file.
To customize hilighing in a file-specific manner, set
'forth-local-words' in a local-variables section at the end of your
source file (*note Variables: (emacs)Local Variables in Files.).

   Example:
     0 [IF]
        Local Variables:
        forth-local-words:
           ((("t:") definition-starter (font-lock-keyword-face . 1)
             "[ \t\n]" t name (font-lock-function-name-face . 3))
            ((";t") definition-ender (font-lock-keyword-face . 1)))
        End:
     [THEN]

13.4 Auto-Indentation
=====================

'forth-mode' automatically tries to indent lines in a smart way,
whenever you type <TAB> or break a line with 'C-m'.

   Simple customization can be achieved by setting 'forth-indent-level'
and 'forth-minor-indent-level' in your '.emacs' file.  For historical
reasons 'gforth.el' indents per default by multiples of 4 columns.  To
use the more traditional 3-column indentation, add the following lines
to your '.emacs':

     (add-hook 'forth-mode-hook (function (lambda ()
        ;; customize variables here:
        (setq forth-indent-level 3)
        (setq forth-minor-indent-level 1)
     )))

   If you want indentation to recognize non-default words, customize it
by setting 'forth-custom-indent-words' in your '.emacs'.  See the
docstring of 'forth-indent-words' for details (in Emacs, type 'C-h v
forth-indent-words').

   To customize indentation in a file-specific manner, set
'forth-local-indent-words' in a local-variables section at the end of
your source file (*note Variables: (emacs)Local Variables in Files.).

   Example:
     0 [IF]
        Local Variables:
        forth-local-indent-words:
           ((("t:") (0 . 2) (0 . 2))
            ((";t") (-2 . 0) (0 . -2)))
        End:
     [THEN]

13.5 Blocks Files
=================

'forth-mode' Autodetects blocks files by checking whether the length of
the first line exceeds 1023 characters.  It then tries to convert the
file into normal text format.  When you save the file, it will be
written to disk as normal stream-source file.

   If you want to write blocks files, use 'forth-blocks-mode'.  It
inherits all the features from 'forth-mode', plus some additions:

   * Files are written to disk in blocks file format.
   * Screen numbers are displayed in the mode line (enumerated beginning
     with the value of 'forth-block-base')
   * Warnings are displayed when lines exceed 64 characters.
   * The beginning of the currently edited block is marked with an
     overlay-arrow.

   There are some restrictions you should be aware of.  When you open a
blocks file that contains tabulator or newline characters, these
characters will be translated into spaces when the file is written back
to disk.  If tabs or newlines are encountered during blocks file
reading, an error is output to the echo area.  So have a look at the
'*Messages*' buffer, when Emacs' bell rings during reading.

   Please consult the docstring of 'forth-blocks-mode' for more
information by typing 'C-h v forth-blocks-mode').

14 Image Files
**************

An image file is a file containing an image of the Forth dictionary,
i.e., compiled Forth code and data residing in the dictionary.  By
convention, we use the extension '.fi' for image files.

14.1 Image Licensing Issues
===========================

An image created with 'gforthmi' (*note gforthmi::) or 'savesystem'
(*note Non-Relocatable Image Files::) includes the original image; i.e.,
according to copyright law it is a derived work of the original image.

   Since Gforth is distributed under the GNU GPL, the newly created
image falls under the GNU GPL, too.  In particular, this means that if
you distribute the image, you have to make all of the sources for the
image available, including those you wrote.  For details see *note GNU
General Public License (Section 3): Copying.

   If you create an image with 'cross' (*note cross.fs::), the image
contains only code compiled from the sources you gave it; if none of
these sources is under the GPL, the terms discussed above do not apply
to the image.  However, if your image needs an engine (a gforth binary)
that is under the GPL, you should make sure that you distribute both in
a way that is at most a _mere aggregation_, if you don't want the terms
of the GPL to apply to the image.

14.2 Image File Background
==========================

Gforth consists not only of primitives (in the engine), but also of
definitions written in Forth.  Since the Forth compiler itself belongs
to those definitions, it is not possible to start the system with the
engine and the Forth source alone.  Therefore we provide the Forth code
as an image file in nearly executable form.  When Gforth starts up, a C
routine loads the image file into memory, optionally relocates the
addresses, then sets up the memory (stacks etc.)  according to
information in the image file, and (finally) starts executing Forth
code.

   The default image file is 'gforth.fi' (in the 'GFORTHPATH').  You can
use a different image by using the '-i', '--image-file' or
'--appl-image' options (*note Invoking Gforth::), e.g.:

     gforth-fast -i myimage.fi

   There are different variants of image files, and they represent
different compromises between the goals of making it easy to generate
image files and making them portable.

   Win32Forth 3.4 and Mitch Bradley's 'cforth' use relocation at
run-time.  This avoids many of the complications discussed below (image
files are data relocatable without further ado), but costs performance
(one addition per memory access) and makes it difficult to pass
addresses between Forth and library calls or other programs.

   By contrast, the Gforth loader performs relocation at image load
time.  The loader also has to replace tokens that represent primitive
calls with the appropriate code-field addresses (or code addresses in
the case of direct threading).

   There are three kinds of image files, with different degrees of
relocatability: non-relocatable, data-relocatable, and fully relocatable
image files.

   These image file variants have several restrictions in common; they
are caused by the design of the image file loader:

   * There is only one segment; in particular, this means, that an image
     file cannot represent 'ALLOCATE'd memory chunks (and pointers to
     them).  The contents of the stacks are not represented, either.

   * The only kinds of relocation supported are: adding the same offset
     to all cells that represent data addresses; and replacing special
     tokens with code addresses or with pieces of machine code.

     If any complex computations involving addresses are performed, the
     results cannot be represented in the image file.  Several
     applications that use such computations come to mind:

        - Hashing addresses (or data structures which contain addresses)
          for table lookup.  If you use Gforth's 'table's or 'wordlist's
          for this purpose, you will have no problem, because the hash
          tables are recomputed automatically when the system is
          started.  If you use your own hash tables, you will have to do
          something similar.

        - There's a cute implementation of doubly-linked lists that uses
          'XOR'ed addresses.  You could represent such lists as
          singly-linked in the image file, and restore the doubly-linked
          representation on startup.(1)

        - The code addresses of run-time routines like 'docol:' cannot
          be represented in the image file (because their tokens would
          be replaced by machine code in direct threaded
          implementations).  As a workaround, compute these addresses at
          run-time with '>code-address' from the executions tokens of
          appropriate words (see the definitions of 'docol:' and friends
          in 'kernel/getdoers.fs').

        - On many architectures addresses are represented in machine
          code in some shifted or mangled form.  You cannot put 'CODE'
          words that contain absolute addresses in this form in a
          relocatable image file.  Workarounds are representing the
          address in some relative form (e.g., relative to the CFA,
          which is present in some register), or loading the address
          from a place where it is stored in a non-mangled form.

   ---------- Footnotes ----------

   (1) In my opinion, though, you should think thrice before using a
doubly-linked list (whatever implementation).

14.3 Non-Relocatable Image Files
================================

These files are simple memory dumps of the dictionary.  They are
specific to the executable (i.e., 'gforth' file) they were created with.
What's worse, they are specific to the place on which the dictionary
resided when the image was created.  Now, there is no guarantee that the
dictionary will reside at the same place the next time you start Gforth,
so there's no guarantee that a non-relocatable image will work the next
time (Gforth will complain instead of crashing, though).  Indeed, on OSs
with (enabled) address-space randomization non-relocatable images are
unlikely to work.

   You can create a non-relocatable image file with 'savesystem', e.g.:

     gforth app.fs -e "savesystem app.fi bye"

'savesystem' ( "image" --  ) gforth-0.2 "savesystem"

14.4 Data-Relocatable Image Files
=================================

These files contain relocatable data addresses, but fixed code addresses
(instead of tokens).  They are specific to the executable (i.e.,
'gforth' file) they were created with.  Also, they disable dynamic
native code generation (typically a factor of 2 in speed).  You get a
data-relocatable image, if you pass the engine you want to use through
the 'GFORTHD' environment variable to 'gforthmi' (*note gforthmi::),
e.g.

     GFORTHD="/usr/bin/gforth-fast --no-dynamic" gforthmi myimage.fi source.fs

   Note that the '--no-dynamic' is required here for the image to work
(otherwise it will contain references to dynamically generated code that
is not saved in the image).

14.5 Fully Relocatable Image Files
==================================

These image files have relocatable data addresses, and tokens for code
addresses.  They can be used with different binaries (e.g., with and
without debugging) on the same machine, and even across machines with
the same data formats (byte order, cell size, floating point format),
and they work with dynamic native code generation.  However, they are
usually specific to the version of Gforth they were created with.  The
files 'gforth.fi' and 'kernl*.fi' are fully relocatable.

   There are two ways to create a fully relocatable image file:

14.5.1 'gforthmi'
-----------------

You will usually use 'gforthmi'.  If you want to create an image file
that contains everything you would load by invoking Gforth with 'gforth
options', you simply say:
     gforthmi file options

   E.g., if you want to create an image 'asm.fi' that has the file
'asm.fs' loaded in addition to the usual stuff, you could do it like
this:

     gforthmi asm.fi asm.fs

   'gforthmi' is implemented as a sh script and works like this: It
produces two non-relocatable images for different addresses and then
compares them.  Its output reflects this: first you see the output (if
any) of the two Gforth invocations that produce the non-relocatable
image files, then you see the output of the comparing program: It
displays the offset used for data addresses and the offset used for code
addresses; moreover, for each cell that cannot be represented correctly
in the image files, it displays a line like this:

          78DC         BFFFFA50         BFFFFA40

   This means that at offset $78dc from 'forthstart', one input image
contains $bffffa50, and the other contains $bffffa40.  Since these cells
cannot be represented correctly in the output image, you should examine
these places in the dictionary and verify that these cells are dead
(i.e., not read before they are written).

   If you insert the option '--application' in front of the image file
name, you will get an image that uses the '--appl-image' option instead
of the '--image-file' option (*note Invoking Gforth::).  When you
execute such an image on Unix (by typing the image name as command), the
Gforth engine will pass all options to the image instead of trying to
interpret them as engine options.

   If you type 'gforthmi' with no arguments, it prints some usage
instructions.

   There are a few wrinkles: After processing the passed options, the
words 'savesystem' and 'bye' must be visible.  A special doubly indirect
threaded version of the 'gforth' executable is used for creating the
non-relocatable images; you can pass the exact filename of this
executable through the environment variable 'GFORTHD' (default:
'gforth-ditc'); if you pass a version that is not doubly indirect
threaded, you will not get a fully relocatable image, but a
data-relocatable image (*note Data-Relocatable Image Files::), because
there is no code address offset).  The normal 'gforth' executable is
used for creating the relocatable image; you can pass the exact filename
of this executable through the environment variable 'GFORTH'.

14.5.2 'cross.fs'
-----------------

You can also use 'cross', a batch compiler that accepts a Forth-like
programming language (*note Cross Compiler::).

   'cross' allows you to create image files for machines with different
data sizes and data formats than the one used for generating the image
file.  You can also use it to create an application image that does not
contain a Forth compiler.  These features are bought with restrictions
and inconveniences in programming.  E.g., addresses have to be stored in
memory with special words ('A!', 'A,', etc.)  in order to make the code
relocatable.

14.6 Stack and Dictionary Sizes
===============================

If you invoke Gforth with a command line flag for the size (*note
Invoking Gforth::), the size you specify is stored in the dictionary.
If you save the dictionary with 'savesystem' or create an image with
'gforthmi', this size will become the default for the resulting image
file.  E.g., the following will create a fully relocatable version of
'gforth.fi' with a 1MB dictionary:

     gforthmi gforth.fi -m 1M

   In other words, if you want to set the default size for the
dictionary and the stacks of an image, just invoke 'gforthmi' with the
appropriate options when creating the image.

   Note: For cache-friendly behaviour (i.e., good performance), you
should make the sizes of the stacks modulo, say, 2K, somewhat different.
E.g., the default stack sizes are: data: 16k (mod 2k=0); fp: 15.5k (mod
2k=1.5k); return: 15k(mod 2k=1k); locals: 14.5k (mod 2k=0.5k).

14.7 Running Image Files
========================

You can invoke Gforth with an image file image instead of the default
'gforth.fi' with the '-i' flag (*note Invoking Gforth::):
     gforth -i image

   If your operating system supports starting scripts with a line of the
form '#! ...', you just have to type the image file name to start Gforth
with this image file (note that the file extension '.fi' is just a
convention).  I.e., to run Gforth with the image file image, you can
just type image instead of 'gforth -i image'.  This works because every
'.fi' file starts with a line of this format:

     #! /usr/local/bin/gforth-0.4.0 -i

   The file and pathname for the Gforth engine specified on this line is
the specific Gforth executable that it was built against; i.e.  the
value of the environment variable 'GFORTH' at the time that 'gforthmi'
was executed.

   You can make use of the same shell capability to make a Forth source
file into an executable.  For example, if you place this text in a file:

     #! /usr/local/bin/gforth

     ." Hello, world" CR
     bye

and then make the file executable (chmod +x in Unix), you can run it
directly from the command line.  The sequence '#!' is used in two ways;
firstly, it is recognised as a "magic sequence" by the operating
system(1) secondly it is treated as a comment character by Gforth.
Because of the second usage, a space is required between '#!' and the
path to the executable (moreover, some Unixes require the sequence '#!
/').

   Most Unix systems (including Linux) support exactly one option after
the binary name.  If that is not enough, you can use the following
trick:

     #! /bin/sh
     : ## ; 0 [if]
     exec gforth -m 10M -d 1M $0 "$@"
     [then]
     ." Hello, world" cr
     bye \ caution: this prevents (further) processing of "$@"

   First this script is interpreted as shell script, which treats the
first two lines as (mostly) comments, then performs the third line,
which invokes gforth with this script ('$0') as parameter and its
parameters as additional parameters ('"$@"').  Then this script is
interpreted as Forth script, which first defines a colon definition
'##', then ignores everything up to '[then]' and finally processes the
following Forth code.  You can also use

     #0 [if]

   in the second line, but this works only in Gforth-0.7.0 and later.

   The 'gforthmi' approach is the fastest one, the shell-based one is
slowest (needs to start an additional shell).  An additional advantage
of the shell approach is that it is unnecessary to know where the Gforth
binary resides, as long as it is in the '$PATH'.

'#!' ( --  ) gforth-0.2 "hash-bang"
   An alias for '\'

   ---------- Footnotes ----------

   (1) The Unix kernel actually recognises two types of files:
executable files and files of data, where the data is processed by an
interpreter that is specified on the "interpreter line" -- the first line
of the file, starting with the sequence #!.  There may be a small limit
(e.g., 32) on the number of characters that may be specified on the
interpreter line.

14.8 Modifying the Startup Sequence
===================================

You can add your own initialization to the startup sequence of an image
through the deferred word ''cold'.  ''cold' is invoked just before the
image-specific command line processing (i.e., loading files and
evaluating ('-e') strings) starts.

   A sequence for adding your initialization usually looks like this:

     :noname
         Defers 'cold \ do other initialization stuff (e.g., rehashing wordlists)
         ... \ your stuff
     ; IS 'cold

   After ''cold', Gforth processes the image options (*note Invoking
Gforth::), and then it performs 'bootmessage', another deferred word.
This normally prints Gforth's startup message and does nothing else.

   So, if you want to make a turnkey image (i.e., an image for an
application instead of an extended Forth system), you can do this in
several ways:

   * If you want to do your interpretation of the OS command-line
     arguments, hook into ''cold'.  In that case you probably also want
     to build the image with 'gforthmi --application' (*note gforthmi::)
     to keep the engine from processing OS command line options.  You
     can then do your own command-line processing with 'next-arg'

   * If you want to have the normal Gforth processing of OS command-line
     arguments, but specify your own command-line options, hook into
     'process-option'.

   * If you want to have more options in addition to the ones that come
     with Gforth, define words into the 'options' vocabulary.

   * If you want to display your own boot message, hook into
     'bootmessage'.

   In either case, you probably do not want the word that you execute in
these hooks to exit normally, but use 'bye' or 'throw'.  Otherwise the
Gforth startup process would continue and eventually present the Forth
command line to the user.

''cold' ( --  ) gforth-0.2 "tick-cold"
   Hook (deferred word) for things to do right before interpreting the
OS command-line arguments.  Normally does some initializations that you
also want to perform.

'bootmessage' ( --  ) gforth-0.4 "bootmessage"
   Hook (deferred word) executed right after interpreting the OS
command-line arguments.  Normally prints the Gforth startup message.

   doc-'quit
'process-option' ( addr u -- true / addr u false  ) gforth-0.7 "process-option"
   Process an option ADDR U, return true, if the option is processed;
unprocessed options are loaded as files throu 'required'.

15 Engine
*********

Reading this chapter is not necessary for programming with Gforth.  It
may be helpful for finding your way in the Gforth sources.

   The ideas in this section have also been published in the following
papers: Bernd Paysan, 'ANS fig/GNU/??? Forth' (in German), Forth-Tagung
'93; M. Anton Ertl, 'A Portable Forth Engine
(https://www.complang.tuwien.ac.at/papers/ertl93.ps.Z)', EuroForth '93;
M. Anton Ertl, 'Threaded code variations and optimizations (extended
version) (https://www.complang.tuwien.ac.at/papers/ertl02.ps.gz)',
Forth-Tagung '02.

15.1 Portability
================

An important goal of the Gforth Project is availability across a wide
range of personal machines.  fig-Forth, and, to a lesser extent, F83,
achieved this goal by manually coding the engine in assembly language
for several then-popular processors.  This approach is very
labor-intensive and the results are short-lived due to progress in
computer architecture.

   Others have avoided this problem by coding in C, e.g., Mitch Bradley
(cforth), Mikael Patel (TILE) and Dirk Zoller (pfe).  This approach is
particularly popular for UNIX-based Forths due to the large variety of
architectures of UNIX machines.  Unfortunately an implementation in C
does not mix well with the goals of efficiency and with using
traditional techniques: Indirect or direct threading cannot be expressed
in C, and switch threading, the fastest technique available in C, is
significantly slower.  Another problem with C is that it is very
cumbersome to express double integer arithmetic.

   Fortunately, there is a portable language that does not have these
limitations: GNU C, the version of C processed by the GNU C compiler
(*note Extensions to the C Language Family: (gcc)C Extensions.).  Its
labels as values feature (*note Labels as Values: (gcc)Labels as
Values.) makes direct and indirect threading possible, its 'long long'
type (*note Double-Word Integers: (gcc)Long Long.) corresponds to
Forth's double numbers on many systems.  GNU C is freely available on
all important (and many unimportant) UNIX machines, VMS, 80386s running
MS-DOS, the Amiga, and the Atari ST, so a Forth written in GNU C can run
on all these machines.

   Writing in a portable language has the reputation of producing code
that is slower than assembly.  For our Forth engine we repeatedly looked
at the code produced by the compiler and eliminated most
compiler-induced inefficiencies by appropriate changes in the source
code.

   However, register allocation cannot be portably influenced by the
programmer, leading to some inefficiencies on register-starved machines.
We use explicit register declarations (*note Variables in Specified
Registers: (gcc)Explicit Reg Vars.) to improve the speed on some
machines.  They are turned on by using the configuration flag
'--enable-force-reg' ('gcc' switch '-DFORCE_REG').  Unfortunately, this
feature not only depends on the machine, but also on the compiler
version: On some machines some compiler versions produce incorrect code
when certain explicit register declarations are used.  So by default
'-DFORCE_REG' is not used.

15.2 Threading
==============

GNU C's labels as values extension (available since 'gcc-2.0', *note
Labels as Values: (gcc)Labels as Values.) makes it possible to take the
address of label by writing '&&label'.  This address can then be used in
a statement like 'goto *address'.  I.e., 'goto *&&x' is the same as
'goto x'.

   With this feature an indirect threaded 'NEXT' looks like:
     cfa = *ip++;
     ca = *cfa;
     goto *ca;
   For those unfamiliar with the names: 'ip' is the Forth instruction
pointer; the 'cfa' (code-field address) corresponds to Standard Forth's
execution token and points to the code field of the next word to be
executed; The 'ca' (code address) fetched from there points to some
executable code, e.g., a primitive or the colon definition handler
'docol'.

   Direct threading is even simpler:
     ca = *ip++;
     goto *ca;

   Of course we have packaged the whole thing neatly in macros called
'NEXT' and 'NEXT1' (the part of 'NEXT' after fetching the cfa).

15.2.1 Scheduling
-----------------

There is a little complication: Pipelined and superscalar processors,
i.e., RISC and some modern CISC machines can process independent
instructions while waiting for the results of an instruction.  The
compiler usually reorders (schedules) the instructions in a way that
achieves good usage of these delay slots.  However, on our first tries
the compiler did not do well on scheduling primitives.  E.g., for '+'
implemented as
     n=sp[0]+sp[1];
     sp++;
     sp[0]=n;
     NEXT;
   the 'NEXT' comes strictly after the other code, i.e., there is nearly
no scheduling.  After a little thought the problem becomes clear: The
compiler cannot know that 'sp' and 'ip' point to different addresses
(and the version of 'gcc' we used would not know it even if it was
possible), so it could not move the load of the cfa above the store to
the TOS. Indeed the pointers could be the same, if code on or very near
the top of stack were executed.  In the interest of speed we chose to
forbid this probably unused "feature" and helped the compiler in
scheduling: 'NEXT' is divided into several parts: 'NEXT_P0', 'NEXT_P1'
and 'NEXT_P2').  '+' now looks like:
     NEXT_P0;
     n=sp[0]+sp[1];
     sp++;
     NEXT_P1;
     sp[0]=n;
     NEXT_P2;

   There are various schemes that distribute the different operations of
NEXT between these parts in several ways; in general, different schemes
perform best on different processors.  We use a scheme for most
architectures that performs well for most processors of this
architecture; in the future we may switch to benchmarking and chosing
the scheme on installation time.

15.2.2 Direct or Indirect Threaded?
-----------------------------------

Threaded forth code consists of references to primitives (simple machine
code routines like '+') and to non-primitives (e.g., colon definitions,
variables, constants); for a specific class of non-primitives (e.g.,
variables) there is one code routine (e.g., 'dovar'), but each variable
needs a separate reference to its data.

   Traditionally Forth has been implemented as indirect threaded code,
because this allows to use only one cell to reference a non-primitive
(basically you point to the data, and find the code address there).

   However, threaded code in Gforth (since 0.6.0) uses two cells for
non-primitives, one for the code address, and one for the data address;
the data pointer is an immediate argument for the virtual machine
instruction represented by the code address.  We call this
_primitive-centric_ threaded code, because all code addresses point to
simple primitives.  E.g., for a variable, the code address is for 'lit'
(also used for integer literals like '99').

   Primitive-centric threaded code allows us to use (faster) direct
threading as dispatch method, completely portably (direct threaded code
in Gforth before 0.6.0 required architecture-specific code).  It also
eliminates the performance problems related to I-cache consistency that
386 implementations have with direct threaded code, and allows
additional optimizations.

   There is a catch, however: the XT parameter of 'execute' can occupy
only one cell, so how do we pass non-primitives with their code _and_
data addresses to them?  Our answer is to use indirect threaded dispatch
for 'execute' and other words that use a single-cell xt.  So, normal
threaded code in colon definitions uses direct threading, and 'execute'
and similar words, which dispatch to xts on the data stack, use indirect
threaded code.  We call this _hybrid direct/indirect_ threaded code.

   The engines 'gforth' and 'gforth-fast' use hybrid direct/indirect
threaded code.  This means that with these engines you cannot use ',' to
compile an xt.  Instead, you have to use 'compile,'.

   If you want to compile xts with ',', use 'gforth-itc'.  This engine
uses plain old indirect threaded code.  It still compiles in a
primitive-centric style, so you cannot use 'compile,' instead of ','
(e.g., for producing tables of xts with '] word1 word2 ... [').  If you
want to do that, you have to use 'gforth-itc' and execute '' , is
compile,'.  Your program can check if it is running on a hybrid
direct/indirect threaded engine or a pure indirect threaded engine with
'threading-method' (*note Threading Words::).

15.2.3 Dynamic Superinstructions
--------------------------------

The engines 'gforth' and 'gforth-fast' use another optimization: Dynamic
superinstructions with replication.  As an example, consider the
following colon definition:

     : squared ( n1 -- n2 )
       dup * ;

   Gforth compiles this into the threaded code sequence

     dup
     *
     ;s

   Use 'simple-see' (*note Examining compiled code::) to see the
threaded code of a colon definition.

   In normal direct threaded code there is a code address occupying one
cell for each of these primitives.  Each code address points to a
machine code routine, and the interpreter jumps to this machine code in
order to execute the primitive.  The routines for these three primitives
are (in 'gforth-fast' on the 386):

     Code dup
     ( $804B950 )  add     esi , # -4  \ $83 $C6 $FC
     ( $804B953 )  add     ebx , # 4  \ $83 $C3 $4
     ( $804B956 )  mov     dword ptr 4 [esi] , ecx  \ $89 $4E $4
     ( $804B959 )  jmp     dword ptr FC [ebx]  \ $FF $63 $FC
     end-code
     Code *
     ( $804ACC4 )  mov     eax , dword ptr 4 [esi]  \ $8B $46 $4
     ( $804ACC7 )  add     esi , # 4  \ $83 $C6 $4
     ( $804ACCA )  add     ebx , # 4  \ $83 $C3 $4
     ( $804ACCD )  imul    ecx , eax  \ $F $AF $C8
     ( $804ACD0 )  jmp     dword ptr FC [ebx]  \ $FF $63 $FC
     end-code
     Code ;s
     ( $804A693 )  mov     eax , dword ptr [edi]  \ $8B $7
     ( $804A695 )  add     edi , # 4  \ $83 $C7 $4
     ( $804A698 )  lea     ebx , dword ptr 4 [eax]  \ $8D $58 $4
     ( $804A69B )  jmp     dword ptr FC [ebx]  \ $FF $63 $FC
     end-code

   With dynamic superinstructions and replication the compiler does not
just lay down the threaded code, but also copies the machine code
fragments, usually without the jump at the end.

     ( $4057D27D )  add     esi , # -4  \ $83 $C6 $FC
     ( $4057D280 )  add     ebx , # 4  \ $83 $C3 $4
     ( $4057D283 )  mov     dword ptr 4 [esi] , ecx  \ $89 $4E $4
     ( $4057D286 )  mov     eax , dword ptr 4 [esi]  \ $8B $46 $4
     ( $4057D289 )  add     esi , # 4  \ $83 $C6 $4
     ( $4057D28C )  add     ebx , # 4  \ $83 $C3 $4
     ( $4057D28F )  imul    ecx , eax  \ $F $AF $C8
     ( $4057D292 )  mov     eax , dword ptr [edi]  \ $8B $7
     ( $4057D294 )  add     edi , # 4  \ $83 $C7 $4
     ( $4057D297 )  lea     ebx , dword ptr 4 [eax]  \ $8D $58 $4
     ( $4057D29A )  jmp     dword ptr FC [ebx]  \ $FF $63 $FC

   Only when a threaded-code control-flow change happens (e.g., in
';s'), the jump is appended.  This optimization eliminates many of these
jumps and makes the rest much more predictable.  The speedup depends on
the processor and the application; on the Athlon and Pentium III this
optimization typically produces a speedup by a factor of 2.

   The code addresses in the direct-threaded code are set to point to
the appropriate points in the copied machine code, in this example like
this:

     primitive  code address
        dup       $4057D27D
        *         $4057D286
        ;s        $4057D292

   Thus there can be threaded-code jumps to any place in this piece of
code.  This also simplifies decompilation quite a bit.

   'See-code' (*note Examining compiled code::) shows the threaded code
intermingled with the native code of dynamic superinstructions.  These
days some additional optimizations are applied for the
dynamically-generated native code, so the output of 'see-code squared'
on 'gforth-fast' on one particular AMD64 installation looks like this:

     $7FB689C678C8 dup    1->2
     7FB68990C1B2:   mov     r15,r8
     $7FB689C678D0 *    2->1
     7FB68990C1B5:   imul    r8,r15
     $7FB689C678D8 ;s    1->1
     7FB68990C1B9:   mov     rbx,[r14]
     7FB68990C1BC:   add     r14,$08
     7FB68990C1C0:   mov     rax,[rbx]
     7FB68990C1C3:   jmp     eax

   You can disable this optimization with '--no-dynamic'.  You can use
the copying without eliminating the jumps (i.e., dynamic replication,
but without superinstructions) with '--no-super'; this gives the branch
prediction benefit alone; the effect on performance depends on the CPU;
on the Athlon and Pentium III the speedup is a little less than for
dynamic superinstructions with replication.

   One use of these options is if you want to patch the threaded code.
With superinstructions, many of the dispatch jumps are eliminated, so
patching often has no effect.  These options preserve all the dispatch
jumps.

   On some machines dynamic superinstructions are disabled by default,
because it is unsafe on these machines.  However, if you feel
adventurous, you can enable it with '--dynamic'.

15.2.4 DOES>
------------

One of the most complex parts of a Forth engine is 'dodoes', i.e., the
chunk of code executed by every word defined by a 'CREATE'...'DOES>'
pair; actually with primitive-centric code, this is only needed if the
xt of the word is 'execute'd.  The main problem here is: How to find the
Forth code to be executed, i.e.  the code after the 'DOES>' (the
'DOES>'-code)?  There are two solutions:

   In fig-Forth the code field points directly to the 'dodoes' and the
'DOES>'-code address is stored in the cell after the code address (i.e.
at 'CFA cell+').  It may seem that this solution is illegal in the
Forth-79 and all later standards, because in fig-Forth this address lies
in the body (which is illegal in these standards).  However, by making
the code field larger for all words this solution becomes legal again.
We use this approach.  Leaving a cell unused in most words is a bit
wasteful, but on the machines we are targeting this is hardly a problem.

15.3 Primitives
===============

15.3.1 Automatic Generation
---------------------------

Since the primitives are implemented in a portable language, there is no
longer any need to minimize the number of primitives.  On the contrary,
having many primitives has an advantage: speed.  In order to reduce the
number of errors in primitives and to make programming them easier, we
provide a tool, the primitive generator ('prims2x.fs' aka Vmgen, *note
Vmgen: (vmgen)Top.), that automatically generates most (and sometimes
all) of the C code for a primitive from the stack effect notation.  The
source for a primitive has the following form:

Forth-name  ( stack-effect )        category    [pronounc.]
['""'glossary entry'""']
C code
[':'
Forth code]

   The items in brackets are optional.  The category and glossary fields
are there for generating the documentation, the Forth code is there for
manual implementations on machines without GNU C. E.g., the source for
the primitive '+' is:
     +    ( n1 n2 -- n )   core    plus
     n = n1+n2;

   This looks like a specification, but in fact 'n = n1+n2' is C code.
Our primitive generation tool extracts a lot of information from the
stack effect notations(1): The number of items popped from and pushed on
the stack, their type, and by what name they are referred to in the C
code.  It then generates a C code prelude and postlude for each
primitive.  The final C code for '+' looks like this:

     I_plus: /* + ( n1 n2 -- n ) */  /* label, stack effect */
     /*  */                          /* documentation */
     NAME("+")                       /* debugging output (with -DDEBUG) */
     {
     DEF_CA                          /* definition of variable ca (indirect threading) */
     Cell n1;                        /* definitions of variables */
     Cell n2;
     Cell n;
     NEXT_P0;                        /* NEXT part 0 */
     n1 = (Cell) sp[1];              /* input */
     n2 = (Cell) TOS;
     sp += 1;                        /* stack adjustment */
     {
     n = n1+n2;                      /* C code taken from the source */
     }
     NEXT_P1;                        /* NEXT part 1 */
     TOS = (Cell)n;                  /* output */
     NEXT_P2;                        /* NEXT part 2 */
     }

   This looks long and inefficient, but the GNU C compiler optimizes
quite well and produces optimal code for '+' on, e.g., the R3000 and the
HP RISC machines: Defining the 'n's does not produce any code, and using
them as intermediate storage also adds no cost.

   There are also other optimizations that are not illustrated by this
example: assignments between simple variables are usually for free (copy
propagation).  If one of the stack items is not used by the primitive
(e.g.  in 'drop'), the compiler eliminates the load from the stack (dead
code elimination).  On the other hand, there are some things that the
compiler does not do, therefore they are performed by 'prims2x.fs': The
compiler does not optimize code away that stores a stack item to the
place where it just came from (e.g., 'over').

   While programming a primitive is usually easy, there are a few cases
where the programmer has to take the actions of the generator into
account, most notably '?dup', but also words that do not (always) fall
through to 'NEXT'.

   For more information

   ---------- Footnotes ----------

   (1) We use a one-stack notation, even though we have separate data
and floating-point stacks; The separate notation can be generated easily
from the unified notation.

15.3.2 TOS Optimization
-----------------------

An important optimization for stack machine emulators, e.g., Forth
engines, is keeping one or more of the top stack items in registers.  If
a word has the stack effect in1...inx '--' out1...outy, keeping the top
n items in registers
   * is better than keeping n-1 items, if x>=n and y>=n, due to fewer
     loads from and stores to the stack.
   * is slower than keeping n-1 items, if x<>y and x<n and y<n, due to
     additional moves between registers.

   In particular, keeping one item in a register is never a
disadvantage, if there are enough registers.  Keeping two items in
registers is a disadvantage for frequent words like '?branch',
constants, variables, literals and 'i'.  Therefore our generator only
produces code that keeps zero or one items in registers.  The generated
C code covers both cases; the selection between these alternatives is
made at C-compile time using the switch '-DUSE_TOS'.  'TOS' in the C
code for '+' is just a simple variable name in the one-item case,
otherwise it is a macro that expands into 'sp[0]'.  Note that the GNU C
compiler tries to keep simple variables like 'TOS' in registers, and it
usually succeeds, if there are enough registers.

   The primitive generator performs the TOS optimization for the
floating-point stack, too ('-DUSE_FTOS').  For floating-point operations
the benefit of this optimization is even larger: floating-point
operations take quite long on most processors, but can be performed in
parallel with other operations as long as their results are not used.
If the FP-TOS is kept in a register, this works.  If it is kept on the
stack, i.e., in memory, the store into memory has to wait for the result
of the floating-point operation, lengthening the execution time of the
primitive considerably.

   The TOS optimization makes the automatic generation of primitives a
bit more complicated.  Just replacing all occurrences of 'sp[0]' by
'TOS' is not sufficient.  There are some special cases to consider:
   * In the case of 'dup ( w -- w w )' the generator must not eliminate
     the store to the original location of the item on the stack, if the
     TOS optimization is turned on.
   * Primitives with stack effects of the form '--' out1...outy must
     store the TOS to the stack at the start.  Likewise, primitives with
     the stack effect in1...inx '--' must load the TOS from the stack at
     the end.  But for the null stack effect '--' no stores or loads
     should be generated.

15.3.3 Produced code
--------------------

To see what assembly code is produced for the primitives on your machine
with your compiler and your flag settings, type 'make engine.s' and look
at the resulting file 'engine.s'.  Alternatively, you can also
disassemble the code of primitives with 'see' on some architectures.

15.4 Performance
================

On RISCs the Gforth engine is very close to optimal; i.e., it is usually
impossible to write a significantly faster threaded-code engine.

   On register-starved machines like the 386 architecture processors
improvements are possible, because 'gcc' does not utilize the registers
as well as a human, even with explicit register declarations; e.g.,
Bernd Beuster wrote a Forth system fragment in assembly language and
hand-tuned it for the 486; this system is 1.19 times faster on the Sieve
benchmark on a 486DX2/66 than Gforth compiled with 'gcc-2.6.3' with
'-DFORCE_REG'.  The situation has improved with gcc-2.95 and
gforth-0.4.9; now the most important virtual machine registers fit in
real registers (and we can even afford to use the TOS optimization),
resulting in a speedup of 1.14 on the sieve over the earlier results.
And dynamic superinstructions provide another speedup (but only around a
factor 1.2 on the 486).

   The potential advantage of assembly language implementations is not
necessarily realized in complete Forth systems: We compared Gforth-0.5.9
(direct threaded, compiled with 'gcc-2.95.1' and '-DFORCE_REG') with
Win32Forth 1.2093 (newer versions are reportedly much faster), LMI's NT
Forth (Beta, May 1994) and Eforth (with and without peephole (aka
pinhole) optimization of the threaded code); all these systems were
written in assembly language.  We also compared Gforth with three
systems written in C: PFE-0.9.14 (compiled with 'gcc-2.6.3' with the
default configuration for Linux: '-O2 -fomit-frame-pointer -DUSE_REGS
-DUNROLL_NEXT'), ThisForth Beta (compiled with 'gcc-2.6.3 -O3
-fomit-frame-pointer'; ThisForth employs peephole optimization of the
threaded code) and TILE (compiled with 'make opt').  We benchmarked
Gforth, PFE, ThisForth and TILE on a 486DX2/66 under Linux.  Kenneth
O'Heskin kindly provided the results for Win32Forth and NT Forth on a
486DX2/66 with similar memory performance under Windows NT. Marcel
Hendrix ported Eforth to Linux, then extended it to run the benchmarks,
added the peephole optimizer, ran the benchmarks and reported the
results.

   We used four small benchmarks: the ubiquitous Sieve; bubble-sorting
and matrix multiplication come from the Stanford integer benchmarks and
have been translated into Forth by Martin Fraeman; we used the versions
included in the TILE Forth package, but with bigger data set sizes; and
a recursive Fibonacci number computation for benchmarking calling
performance.  The following table shows the time taken for the
benchmarks scaled by the time taken by Gforth (in other words, it shows
the speedup factor that Gforth achieved over the other systems).

     relative       Win32-    NT       eforth       This-
     time     Gforth Forth Forth eforth  +opt   PFE Forth  TILE
     sieve      1.00  2.16  1.78   2.16  1.32  2.46  4.96 13.37
     bubble     1.00  1.93  2.07   2.18  1.29  2.21        5.70
     matmul     1.00  1.92  1.76   1.90  0.96  2.06        5.32
     fib        1.00  2.32  2.03   1.86  1.31  2.64  4.55  6.54

   You may be quite surprised by the good performance of Gforth when
compared with systems written in assembly language.  One important
reason for the disappointing performance of these other systems is
probably that they are not written optimally for the 486 (e.g., they use
the 'lods' instruction).  In addition, Win32Forth uses a comfortable,
but costly method for relocating the Forth image: like 'cforth', it
computes the actual addresses at run time, resulting in two address
computations per 'NEXT' (*note Image File Background::).

   The speedup of Gforth over PFE, ThisForth and TILE can be easily
explained with the self-imposed restriction of the latter systems to
standard C, which makes efficient threading impossible (however, the
measured implementation of PFE uses a GNU C extension: *note Defining
Global Register Variables: (gcc)Global Reg Vars.).  Moreover, current C
compilers have a hard time optimizing other aspects of the ThisForth and
the TILE source.

   The performance of Gforth on 386 architecture processors varies
widely with the version of 'gcc' used.  E.g., 'gcc-2.5.8' failed to
allocate any of the virtual machine registers into real machine
registers by itself and would not work correctly with explicit register
declarations, giving a significantly slower engine (on a 486DX2/66
running the Sieve) than the one measured above.

   Note that there have been several releases of Win32Forth since the
release presented here, so the results presented above may have little
predictive value for the performance of Win32Forth today (results for
the current release on an i486DX2/66 are welcome).

   In 'Translating Forth to Efficient C
(https://www.complang.tuwien.ac.at/papers/ertl&maierhofer95.ps.gz)' by
M. Anton Ertl and Martin Maierhofer (presented at EuroForth '95), an
indirect threaded version of Gforth is compared with Win32Forth, NT
Forth, PFE, ThisForth, and several native code systems; that version of
Gforth is slower on a 486 than the version used here.  You can find a
newer version of these measurements at
<https://www.complang.tuwien.ac.at/forth/performance.html>.  You can
find numbers for Gforth on various machines in 'Benchres'.

16 Cross Compiler
*****************

The cross compiler is used to bootstrap a Forth kernel.  Since Gforth is
mostly written in Forth, including crucial parts like the outer
interpreter and compiler, it needs compiled Forth code to get started.
The cross compiler allows to create new images for other architectures,
even running under another Forth system.

16.1 Using the Cross Compiler
=============================

The cross compiler uses a language that resembles Forth, but isn't.  The
main difference is that you can execute Forth code after definition,
while you usually can't execute the code compiled by cross, because the
code you are compiling is typically for a different computer than the
one you are compiling on.

   The Makefile is already set up to allow you to create kernels for new
architectures with a simple make command.  The generic kernels using the
GCC compiled virtual machine are created in the normal build process
with 'make'.  To create a embedded Gforth executable for e.g.  the 8086
processor (running on a DOS machine), type

     make kernl-8086.fi

   This will use the machine description from the 'arch/8086' directory
to create a new kernel.  A machine file may look like that:

     \ Parameter for target systems                         06oct92py

         4 Constant cell             \ cell size in bytes
         2 Constant cell<<           \ cell shift to bytes
         5 Constant cell>bit         \ cell shift to bits
         8 Constant bits/char        \ bits per character
         8 Constant bits/byte        \ bits per byte [default: 8]
         8 Constant float            \ bytes per float
         8 Constant /maxalign        \ maximum alignment in bytes
     false Constant bigendian        \ byte order
     ( true=big, false=little )

     include machpc.fs               \ feature list

   This part is obligatory for the cross compiler itself, the feature
list is used by the kernel to conditionally compile some features in and
out, depending on whether the target supports these features.

   There are some optional features, if you define your own primitives,
have an assembler, or need special, nonstandard preparation to make the
boot process work.  'asm-include' includes an assembler, 'prims-include'
includes primitives, and '>boot' prepares for booting.

     : asm-include    ." Include assembler" cr
       s" arch/8086/asm.fs" included ;

     : prims-include  ." Include primitives" cr
       s" arch/8086/prim.fs" included ;

     : >boot          ." Prepare booting" cr
       s" ' boot >body into-forth 1+ !" evaluate ;

   These words are used as sort of macro during the cross compilation in
the file 'kernel/main.fs'.  Instead of using these macros, it would be
possible --- but more complicated --- to write a new kernel project file,
too.

   'kernel/main.fs' expects the machine description file name on the
stack; the cross compiler itself ('cross.fs') assumes that either
'mach-file' leaves a counted string on the stack, or 'machine-file'
leaves an address, count pair of the filename on the stack.

   The feature list is typically controlled using 'SetValue', generic
files that are used by several projects can use 'DefaultValue' instead.
Both functions work like 'Value', when the value isn't defined, but
'SetValue' works like 'to' if the value is defined, and 'DefaultValue'
doesn't set anything, if the value is defined.

     \ generic mach file for pc gforth                       03sep97jaw

     true DefaultValue NIL  \ relocating

     >ENVIRON

     true DefaultValue file          \ controls the presence of the
                                     \ file access wordset
     true DefaultValue OS            \ flag to indicate a operating system

     true DefaultValue prims         \ true: primitives are c-code

     true DefaultValue floating      \ floating point wordset is present

     true DefaultValue glocals       \ gforth locals are present
                                     \ will be loaded
     true DefaultValue dcomps        \ double number comparisons

     true DefaultValue hash          \ hashing primitives are loaded/present

     true DefaultValue xconds        \ used together with glocals,
                                     \ special conditionals supporting gforths'
                                     \ local variables
     true DefaultValue header        \ save a header information

     true DefaultValue backtrace     \ enables backtrace code

     false DefaultValue ec
     false DefaultValue crlf

     cell 2 = [IF] &32 [ELSE] &256 [THEN] KB DefaultValue kernel-size

     &16 KB          DefaultValue stack-size
     &15 KB &512 +   DefaultValue fstack-size
     &15 KB          DefaultValue rstack-size
     &14 KB &512 +   DefaultValue lstack-size

16.2 How the Cross Compiler Works
=================================

17 MINOS2, a GUI library
************************

17.1 MINOS2 object framework
============================

MINOS2 is a GUI library, written in 'mini-oof2.fs''s object model.  It
has two main class hierarchies:

'actor' ( -- class  ) minos2 "actor"
   class for the actions bound to a component.

'widget' ( -- class  ) minos2 "widget"
   class for visual components

17.1.1 'actor' methods:
-----------------------

'caller-w' ( -- optr  ) minos2 "caller-w"
   pointer back to the widget embedding the actor

'active-w' ( -- optr  ) minos2 "active-w"
   pointer to the active subwidget embedding the actor

'act-name$' ( -- addr u  ) minos2 "act-name-string"
   Debugging aid: name of the actor

'clicked' ( rx ry bmask n --  ) minos2 "clicked"
   processed clicks

'scrolled' ( axis dir --  ) minos2 "scrolled"
   process scrolling

'touchdown' ( $rxy*n bmask --  ) minos2 "touchdown"
   raw click down

'touchup' ( $rxy*n bmask --  ) minos2 "touchup"
   raw click up

'ukeyed' ( addr u --  ) minos2 "ukeyed"
   key event, string of printable unicode characters

'ekeyed' ( ekey --  ) minos2 "ekeyed"
   key event, non-printable key

'?inside' ( rx ry -- act / 0  ) minos2 "query-inside"
   check if coordinates are inside the widget

'focus' ( --  ) minos2 "focus"
   put widget into focus

'defocus' ( --  ) minos2 "defocus"
   put widget out of focus

'entered' ( --  ) minos2 "entered"
   react on cursor entering the widget area

'left' ( --  ) minos2 "left"
   react on cursor leaving the widget area

'show' ( --  ) minos2 "show"
   widget is shown

'hide' ( --  ) minos2 "hide"
   widget is hidden

'get' ( -- something  ) minos2 "get"
   getter for the value behind the widget

'set' ( something --  ) minos2 "set"
   setter for the value behind the widget

'show-you' ( --  ) minos2 "show-you"
   make widget visible

17.1.2 'widget' methods:
------------------------

'parent-w' ( -- optr  ) minos2 "parent-w"
   pointer to parent widget

'act' ( -- optr  ) minos2 "act"
   pointer to actor

'name$' ( -- addr u  ) minos2 "name-string"
   Widget name for debugging and searching

'x' ( -- r  ) minos2 "x"
   widget x coordinate

'y' ( -- r  ) minos2 "y"
   widget y coordinate

'w' ( -- r  ) minos2 "w"
   widget width

'h' ( -- r  ) minos2 "h"
   widget height above baseline

'd' ( -- r  ) minos2 "d"
   widget depth below baseline

'gap' ( -- r  ) minos2 "gap"
   gap between lines

'baseline' ( -- r  ) minos2 "baseline"
   minimun skip per line

'kerning' ( -- r  ) minos2 "kerning"
   add kerning

'raise' ( -- r  ) minos2 "raise"
   raise/lower box

'border' ( -- r  ) minos2 "border"
   surrounding border, all directions

'borderv' ( -- r  ) minos2 "borderv"
   vertical border offset

'bordert' ( -- r  ) minos2 "bordert"
   top border offset

'borderl' ( -- r  ) minos2 "borderl"
   left border offset

'w-color' ( -- r  ) minos2 "w-color"
   widget color index (into color map), if any

'draw-init' ( --  ) minos2 "draw-init"
   init draw

'draw' ( --  ) minos2 "draw"
   draw widget

'split' ( firstflag rstart1 rx -- o rstart2  ) minos2 "split"
   split a widget into parts for typesetting paragraphs

'lastfit' ( --  ) minos2 "lastfit"
   fit last widget element in a box

'hglue' ( -- rtyp rsub radd  ) minos2 "hglue"
   calculate horizontal glue

'dglue' ( -- rtyp rsub radd  ) minos2 "dglue"
   calculate vertical glue below baseline

'vglue' ( -- rtyp rsub radd  ) minos2 "vglue"
   calculate vertical glue above baseline

'hglue@' ( -- rtyp rsub radd  ) minos2 "hglue-fetch"
   cached variant of 'hglue'

'dglue@' ( -- rtyp rsub radd  ) minos2 "dglue-fetch"
   cached variant of 'dglue'

'vglue@' ( -- rtyp rsub radd  ) minos2 "vglue-fetch"
   cached variant of 'vglue'

'xywh' ( -- rx0 ry0 rw rh  ) minos2 "xywh"
   widget bounding box, starting at the top left corner

'xywhd' ( -- rx ry rw rh rd  ) minos2 "xywhd"
   widget bounding box, starting at the left baseline point

'!resize' ( rx ry rw rh rd --  ) minos2 "store-resize"
   resize a widget

'!size' ( --  ) minos2 "store-size"
   let the widget self-determine its size

'dispose-widget' ( --  ) minos2 "dispose-widget"
   get rid of a widget

'.widget' ( --  ) minos2 "print-widget"
   debugging: Print informations about the widget

'par-split' ( rw --  ) minos2 "par-split"
   split a paragraph by width RW

'resized' ( --  ) minos2 "resized"
   widget is resized

   Components are composed using a boxes&glue model similar to LaTeX,
including paragraph breaking.  For the sake of simplicity and
portability, MINOS2 only supports a single window, and uses OpenGL for
rendering.

   MINOS2 furthermore supports animations with the 'animation' class.  A
color index texture is used for different color schemes, and transition
between neighboring schemes can also be animated.

'>animate' ( rdelta addr xt --  ) minos2 "to-animate"
   create a new animation, calling XT with stack effect '( addr r0..1 --
)' repeatedly, until the RDELTA timeout expired; last call is always
with argument 1E for the time.

   You can create named color indexes and assign them color values for
the currently active color scheme.

'color:' ( rgba "name" --  ) minos2 "color:"
   Create a (possibly shared) color index initialized with RGBA

'new-color:' ( rgba "name" --  ) minos2 "new-color:"
   Create a unique color index initialized with RGBA

'text-color:' ( rgba "name" --  ) minos2 "text-color:"
   Create a unique text color index initialized with RGBA, the
corresponding emoji color is set to white.

'text-emoji-color:' ( rgbatext rgbaemoji "name" --  ) minos2 "text-emoji-color:"
   Create a unique text color index initialized with RGBATEXT, the
corresponding emoji color is set to RGBAEMOJI.

'fade-color:' ( rgba1 rgba2 "name" --  ) minos2 "fade-color:"
   Create a unique pair of text color index initialized with RGBA1 and
RGBA2, the corresponding emoji color is set to white.  By slowly
shifting the index from one to the next index, the object will shift its
color using a linear interpolation when redrawn.

'text-emoji-fade-color:' ( rgbatext1 ~2 rgbaemoji1 ~2 "name" --  ) minos2 "text-emoji-fade-color:"
   Create a unique pair of text color index initialized with RGBATEXT1
and ~2, the corresponding emoji color pair is set to RGBAEMOJI1 to ~2.
By slowly shifting the index from one to the next index, the object will
shift its color using a linear interpolation when redrawn.

're-color' ( rgba "name" --  ) minos2 "re-color"
   assign the named color index "NAME" in the current color scheme with
the value RGBA.

're-text-color' ( rgba "name" --  ) minos2 "re-text-color"
   assign the named text color index "NAME" in the current color scheme
with the value RGBA.

're-emoji-color' ( rgbatext rgbaemoji "name" --  ) minos2 "re-emoji-color"
   assign the named text and emoji color index "NAME" in the current
color scheme with the value RGBATEXT and RGBAEMOJI.

're-fade-color' ( rgba1 rgba2 "name" --  ) minos2 "re-fade-color"
   assign the named color index pair "NAME" in the current color scheme
with the value RGBA1 and RGBA2.

're-text-emoji-fade-color' ( rgbatext1 ~2 rgbaemoji1 ~2 "name" --  ) minos2 "re-text-emoji-fade-color"
   assign the named color index pair "NAME" in the current color scheme
with the value RGBATEXT1 and ~2 resp.  RGBAEMOJI1 and ~2.

   For a number of specific objects, there are early bound methods, that
only work on these objects

   * Viewport

     'vp-top' ( o:vp --  ) minos2 "vp-top"
     scroll viewport to top

     'vp-bottom' ( o:vp --  ) minos2 "vp-bottom"
     scroll viewport to bottom

     'vp-left' ( o:vp --  ) minos2 "vp-left"
     scroll viewport to left

     'vp-right' ( o:vp --  ) minos2 "vp-right"
     scroll viewport to right

     'vp-reslide' ( o:vp --  ) minos2 "vp-reslide"
     Adjust the sliders of a viewport after scrolling

     'vp-needed' ( xt --  ) minos2 "vp-needed"
     collect needs in viewport's vp-need

17.2 MINOS2 tutorial
====================

Tutorials are small files, each showing a bit of MINOS2.  For the common
framework, the file 'minos2/tutorial/tutorial.fs' needs to be loaded
first; all other tutorials in the command line argument are included
from within that file.  Scroll wheel or previous/next mouse buttons as
well as clicking on the left or right edge of the window allow
navigation between the different tutorials loaded.

   I.e.  to load the buttons tutorial, you start Gforth with

     gforth minos2/tutorial/tutorial.fs buttons.fs

   Available tutorials:

   * 'buttons.fs': Clickable buttons

   * 'plots.fs': Plot functions

   * 'markdown.fs': Markdown document viewer

   * 'screenshot.fs': Screenshot function

Appendix A Bugs
***************

Known bugs are described in the file 'BUGS' in the Gforth distribution.

   If you find a bug, please submit a bug report through
<https://savannah.gnu.org/bugs/?func=addbug&group=gforth>.

   * A program (or a sequence of keyboard commands) that reproduces the
     bug.
   * A description of what you think constitutes the buggy behaviour.
   * The Gforth version used (it is announced at the start of an
     interactive Gforth session).
   * The machine and operating system (on Unix systems 'uname -a' will
     report this information).
   * The installation options (you can find the configure options at the
     start of 'config.status') and configuration ('configure' output or
     'config.cache').
   * A complete list of changes (if any) you (or your installer) have
     made to the Gforth sources.

   For a thorough guide on reporting bugs read *note How to Report Bugs:
(gcc)Bug Reporting.

Appendix B Authors and Ancestors of Gforth
******************************************

B.1 Authors and Contributors
============================

The Gforth project was started in mid-1992 by Bernd Paysan and Anton
Ertl.  The third major author was Jens Wilke.  Neal Crook contributed a
lot to the manual.  Assemblers and disassemblers were contributed by
Andrew McKewan, Christian Pirker, Bernd Thallner, and Michal Revucky.
Lennart Benschop (who was one of Gforth's first users, in mid-1993) and
Stuart Ramsden inspired us with their continuous feedback.  Lennart
Benshop contributed 'glosgen.fs', while Stuart Ramsden has been working
on automatic support for calling C libraries.  Helpful comments also
came from Paul Kleinrubatscher, Christian Pirker, Dirk Zoller, Marcel
Hendrix, John Wavrik, Barrie Stott, Marc de Groot, Jorge Acerada, Bruce
Hoyt, Robert Epprecht, Dennis Ruffer and David N. Williams.  Since the
release of Gforth-0.2.1 there were also helpful comments from many
others; thank you all, sorry for not listing you here (but digging
through my mailbox to extract your names is on my to-do list).

   Gforth also owes a lot to the authors of the tools we used (GCC, CVS,
and autoconf, among others), and to the creators of the Internet: Gforth
was developed across the Internet, and its authors did not meet
physically for the first 4 years of development.

B.2 Pedigree
============

Gforth descends from bigFORTH (1993) and fig-Forth.  Of course, a
significant part of the design of Gforth was prescribed by Standard
Forth.

   Bernd Paysan wrote bigFORTH, a descendent from TurboForth, an
unreleased 32 bit native code version of VolksForth for the Atari ST,
written mostly by Dietrich Weineck.

   VolksForth was written by Klaus Schleisiek, Bernd Pennemann, Georg
Rehfeld and Dietrich Weineck for the C64 (called UltraForth there) in
the mid-80s and ported to the Atari ST in 1986.  It descends from
fig-Forth.

   A team led by Bill Ragsdale implemented fig-Forth on many processors
in 1979.  Robert Selzer and Bill Ragsdale developed the original
implementation of fig-Forth for the 6502 based on microForth.

   The principal architect of microForth was Dean Sanderson.  microForth
was FORTH, Inc.'s first off-the-shelf product.  It was developed in 1976
for the 1802, and subsequently implemented on the 8080, the 6800 and the
Z80.

   All earlier Forth systems were custom-made, usually by Charles Moore,
who discovered (as he puts it) Forth during the late 60s.  The first
full Forth existed in 1971.

   A part of the information in this section comes from 'The Evolution
of Forth (https://www.forth.com/resources/evolution/index.html)' by
Elizabeth D. Rather, Donald R. Colburn and Charles H. Moore, presented
at the HOPL-II conference and preprinted in SIGPLAN Notices 28(3), 1993.
You can find more historical and genealogical information about Forth
there.  For a more general (and graphical) Forth family tree look see
'<https://www.complang.tuwien.ac.at/forth/family-tree/>, Forth Family
Tree and Timeline'.

Appendix C Other Forth-related information
******************************************

There is an active news group (comp.lang.forth) discussing Forth
(including Gforth) and Forth-related issues.  Its FAQs
(https://www.complang.tuwien.ac.at/forth/faq/faq-general-2.html)
(frequently asked questions and their answers) contains a lot of
information on Forth.  You should read it before posting to
comp.lang.forth.

   The Forth standard is most usable in its HTML form
(https://forth-standard.org/).

Appendix D Licenses
*******************

D.1 GNU Free Documentation License
==================================

                      Version 1.2, November 2002

     Copyright © 2000,2001,2002 Free Software Foundation, Inc.
     59 Temple Place, Suite 330, Boston, MA  02111-1307, USA

     Everyone is permitted to copy and distribute verbatim copies
     of this license document, but changing it is not allowed.

  0. PREAMBLE

     The purpose of this License is to make a manual, textbook, or other
     functional and useful document "free" in the sense of freedom: to
     assure everyone the effective freedom to copy and redistribute it,
     with or without modifying it, either commercially or
     noncommercially.  Secondarily, this License preserves for the
     author and publisher a way to get credit for their work, while not
     being considered responsible for modifications made by others.

     This License is a kind of "copyleft", which means that derivative
     works of the document must themselves be free in the same sense.
     It complements the GNU General Public License, which is a copyleft
     license designed for free software.

     We have designed this License in order to use it for manuals for
     free software, because free software needs free documentation: a
     free program should come with manuals providing the same freedoms
     that the software does.  But this License is not limited to
     software manuals; it can be used for any textual work, regardless
     of subject matter or whether it is published as a printed book.  We
     recommend this License principally for works whose purpose is
     instruction or reference.

  1. APPLICABILITY AND DEFINITIONS

     This License applies to any manual or other work, in any medium,
     that contains a notice placed by the copyright holder saying it can
     be distributed under the terms of this License.  Such a notice
     grants a world-wide, royalty-free license, unlimited in duration,
     to use that work under the conditions stated herein.  The
     "Document", below, refers to any such manual or work.  Any member
     of the public is a licensee, and is addressed as "you".  You accept
     the license if you copy, modify or distribute the work in a way
     requiring permission under copyright law.

     A "Modified Version" of the Document means any work containing the
     Document or a portion of it, either copied verbatim, or with
     modifications and/or translated into another language.

     A "Secondary Section" is a named appendix or a front-matter section
     of the Document that deals exclusively with the relationship of the
     publishers or authors of the Document to the Document's overall
     subject (or to related matters) and contains nothing that could
     fall directly within that overall subject.  (Thus, if the Document
     is in part a textbook of mathematics, a Secondary Section may not
     explain any mathematics.)  The relationship could be a matter of
     historical connection with the subject or with related matters, or
     of legal, commercial, philosophical, ethical or political position
     regarding them.

     The "Invariant Sections" are certain Secondary Sections whose
     titles are designated, as being those of Invariant Sections, in the
     notice that says that the Document is released under this License.
     If a section does not fit the above definition of Secondary then it
     is not allowed to be designated as Invariant.  The Document may
     contain zero Invariant Sections.  If the Document does not identify
     any Invariant Sections then there are none.

     The "Cover Texts" are certain short passages of text that are
     listed, as Front-Cover Texts or Back-Cover Texts, in the notice
     that says that the Document is released under this License.  A
     Front-Cover Text may be at most 5 words, and a Back-Cover Text may
     be at most 25 words.

     A "Transparent" copy of the Document means a machine-readable copy,
     represented in a format whose specification is available to the
     general public, that is suitable for revising the document
     straightforwardly with generic text editors or (for images composed
     of pixels) generic paint programs or (for drawings) some widely
     available drawing editor, and that is suitable for input to text
     formatters or for automatic translation to a variety of formats
     suitable for input to text formatters.  A copy made in an otherwise
     Transparent file format whose markup, or absence of markup, has
     been arranged to thwart or discourage subsequent modification by
     readers is not Transparent.  An image format is not Transparent if
     used for any substantial amount of text.  A copy that is not
     "Transparent" is called "Opaque".

     Examples of suitable formats for Transparent copies include plain
     ASCII without markup, Texinfo input format, LaTeX input format,
     SGML or XML using a publicly available DTD, and standard-conforming
     simple HTML, PostScript or PDF designed for human modification.
     Examples of transparent image formats include PNG, XCF and JPG.
     Opaque formats include proprietary formats that can be read and
     edited only by proprietary word processors, SGML or XML for which
     the DTD and/or processing tools are not generally available, and
     the machine-generated HTML, PostScript or PDF produced by some word
     processors for output purposes only.

     The "Title Page" means, for a printed book, the title page itself,
     plus such following pages as are needed to hold, legibly, the
     material this License requires to appear in the title page.  For
     works in formats which do not have any title page as such, "Title
     Page" means the text near the most prominent appearance of the
     work's title, preceding the beginning of the body of the text.

     A section "Entitled XYZ" means a named subunit of the Document
     whose title either is precisely XYZ or contains XYZ in parentheses
     following text that translates XYZ in another language.  (Here XYZ
     stands for a specific section name mentioned below, such as
     "Acknowledgements", "Dedications", "Endorsements", or "History".)
     To "Preserve the Title" of such a section when you modify the
     Document means that it remains a section "Entitled XYZ" according
     to this definition.

     The Document may include Warranty Disclaimers next to the notice
     which states that this License applies to the Document.  These
     Warranty Disclaimers are considered to be included by reference in
     this License, but only as regards disclaiming warranties: any other
     implication that these Warranty Disclaimers may have is void and
     has no effect on the meaning of this License.

  2. VERBATIM COPYING

     You may copy and distribute the Document in any medium, either
     commercially or noncommercially, provided that this License, the
     copyright notices, and the license notice saying this License
     applies to the Document are reproduced in all copies, and that you
     add no other conditions whatsoever to those of this License.  You
     may not use technical measures to obstruct or control the reading
     or further copying of the copies you make or distribute.  However,
     you may accept compensation in exchange for copies.  If you
     distribute a large enough number of copies you must also follow the
     conditions in section 3.

     You may also lend copies, under the same conditions stated above,
     and you may publicly display copies.

  3. COPYING IN QUANTITY

     If you publish printed copies (or copies in media that commonly
     have printed covers) of the Document, numbering more than 100, and
     the Document's license notice requires Cover Texts, you must
     enclose the copies in covers that carry, clearly and legibly, all
     these Cover Texts: Front-Cover Texts on the front cover, and
     Back-Cover Texts on the back cover.  Both covers must also clearly
     and legibly identify you as the publisher of these copies.  The
     front cover must present the full title with all words of the title
     equally prominent and visible.  You may add other material on the
     covers in addition.  Copying with changes limited to the covers, as
     long as they preserve the title of the Document and satisfy these
     conditions, can be treated as verbatim copying in other respects.

     If the required texts for either cover are too voluminous to fit
     legibly, you should put the first ones listed (as many as fit
     reasonably) on the actual cover, and continue the rest onto
     adjacent pages.

     If you publish or distribute Opaque copies of the Document
     numbering more than 100, you must either include a machine-readable
     Transparent copy along with each Opaque copy, or state in or with
     each Opaque copy a computer-network location from which the general
     network-using public has access to download using public-standard
     network protocols a complete Transparent copy of the Document, free
     of added material.  If you use the latter option, you must take
     reasonably prudent steps, when you begin distribution of Opaque
     copies in quantity, to ensure that this Transparent copy will
     remain thus accessible at the stated location until at least one
     year after the last time you distribute an Opaque copy (directly or
     through your agents or retailers) of that edition to the public.

     It is requested, but not required, that you contact the authors of
     the Document well before redistributing any large number of copies,
     to give them a chance to provide you with an updated version of the
     Document.

  4. MODIFICATIONS

     You may copy and distribute a Modified Version of the Document
     under the conditions of sections 2 and 3 above, provided that you
     release the Modified Version under precisely this License, with the
     Modified Version filling the role of the Document, thus licensing
     distribution and modification of the Modified Version to whoever
     possesses a copy of it.  In addition, you must do these things in
     the Modified Version:

       A. Use in the Title Page (and on the covers, if any) a title
          distinct from that of the Document, and from those of previous
          versions (which should, if there were any, be listed in the
          History section of the Document).  You may use the same title
          as a previous version if the original publisher of that
          version gives permission.

       B. List on the Title Page, as authors, one or more persons or
          entities responsible for authorship of the modifications in
          the Modified Version, together with at least five of the
          principal authors of the Document (all of its principal
          authors, if it has fewer than five), unless they release you
          from this requirement.

       C. State on the Title page the name of the publisher of the
          Modified Version, as the publisher.

       D. Preserve all the copyright notices of the Document.

       E. Add an appropriate copyright notice for your modifications
          adjacent to the other copyright notices.

       F. Include, immediately after the copyright notices, a license
          notice giving the public permission to use the Modified
          Version under the terms of this License, in the form shown in
          the Addendum below.

       G. Preserve in that license notice the full lists of Invariant
          Sections and required Cover Texts given in the Document's
          license notice.

       H. Include an unaltered copy of this License.

       I. Preserve the section Entitled "History", Preserve its Title,
          and add to it an item stating at least the title, year, new
          authors, and publisher of the Modified Version as given on the
          Title Page.  If there is no section Entitled "History" in the
          Document, create one stating the title, year, authors, and
          publisher of the Document as given on its Title Page, then add
          an item describing the Modified Version as stated in the
          previous sentence.

       J. Preserve the network location, if any, given in the Document
          for public access to a Transparent copy of the Document, and
          likewise the network locations given in the Document for
          previous versions it was based on.  These may be placed in the
          "History" section.  You may omit a network location for a work
          that was published at least four years before the Document
          itself, or if the original publisher of the version it refers
          to gives permission.

       K. For any section Entitled "Acknowledgements" or "Dedications",
          Preserve the Title of the section, and preserve in the section
          all the substance and tone of each of the contributor
          acknowledgements and/or dedications given therein.

       L. Preserve all the Invariant Sections of the Document, unaltered
          in their text and in their titles.  Section numbers or the
          equivalent are not considered part of the section titles.

       M. Delete any section Entitled "Endorsements".  Such a section
          may not be included in the Modified Version.

       N. Do not retitle any existing section to be Entitled
          "Endorsements" or to conflict in title with any Invariant
          Section.

       O. Preserve any Warranty Disclaimers.

     If the Modified Version includes new front-matter sections or
     appendices that qualify as Secondary Sections and contain no
     material copied from the Document, you may at your option designate
     some or all of these sections as invariant.  To do this, add their
     titles to the list of Invariant Sections in the Modified Version's
     license notice.  These titles must be distinct from any other
     section titles.

     You may add a section Entitled "Endorsements", provided it contains
     nothing but endorsements of your Modified Version by various
     parties---for example, statements of peer review or that the text has
     been approved by an organization as the authoritative definition of
     a standard.

     You may add a passage of up to five words as a Front-Cover Text,
     and a passage of up to 25 words as a Back-Cover Text, to the end of
     the list of Cover Texts in the Modified Version.  Only one passage
     of Front-Cover Text and one of Back-Cover Text may be added by (or
     through arrangements made by) any one entity.  If the Document
     already includes a cover text for the same cover, previously added
     by you or by arrangement made by the same entity you are acting on
     behalf of, you may not add another; but you may replace the old
     one, on explicit permission from the previous publisher that added
     the old one.

     The author(s) and publisher(s) of the Document do not by this
     License give permission to use their names for publicity for or to
     assert or imply endorsement of any Modified Version.

  5. COMBINING DOCUMENTS

     You may combine the Document with other documents released under
     this License, under the terms defined in section 4 above for
     modified versions, provided that you include in the combination all
     of the Invariant Sections of all of the original documents,
     unmodified, and list them all as Invariant Sections of your
     combined work in its license notice, and that you preserve all
     their Warranty Disclaimers.

     The combined work need only contain one copy of this License, and
     multiple identical Invariant Sections may be replaced with a single
     copy.  If there are multiple Invariant Sections with the same name
     but different contents, make the title of each such section unique
     by adding at the end of it, in parentheses, the name of the
     original author or publisher of that section if known, or else a
     unique number.  Make the same adjustment to the section titles in
     the list of Invariant Sections in the license notice of the
     combined work.

     In the combination, you must combine any sections Entitled
     "History" in the various original documents, forming one section
     Entitled "History"; likewise combine any sections Entitled
     "Acknowledgements", and any sections Entitled "Dedications".  You
     must delete all sections Entitled "Endorsements."

  6. COLLECTIONS OF DOCUMENTS

     You may make a collection consisting of the Document and other
     documents released under this License, and replace the individual
     copies of this License in the various documents with a single copy
     that is included in the collection, provided that you follow the
     rules of this License for verbatim copying of each of the documents
     in all other respects.

     You may extract a single document from such a collection, and
     distribute it individually under this License, provided you insert
     a copy of this License into the extracted document, and follow this
     License in all other respects regarding verbatim copying of that
     document.

  7. AGGREGATION WITH INDEPENDENT WORKS

     A compilation of the Document or its derivatives with other
     separate and independent documents or works, in or on a volume of a
     storage or distribution medium, is called an "aggregate" if the
     copyright resulting from the compilation is not used to limit the
     legal rights of the compilation's users beyond what the individual
     works permit.  When the Document is included in an aggregate, this
     License does not apply to the other works in the aggregate which
     are not themselves derivative works of the Document.

     If the Cover Text requirement of section 3 is applicable to these
     copies of the Document, then if the Document is less than one half
     of the entire aggregate, the Document's Cover Texts may be placed
     on covers that bracket the Document within the aggregate, or the
     electronic equivalent of covers if the Document is in electronic
     form.  Otherwise they must appear on printed covers that bracket
     the whole aggregate.

  8. TRANSLATION

     Translation is considered a kind of modification, so you may
     distribute translations of the Document under the terms of section
     4.  Replacing Invariant Sections with translations requires special
     permission from their copyright holders, but you may include
     translations of some or all Invariant Sections in addition to the
     original versions of these Invariant Sections.  You may include a
     translation of this License, and all the license notices in the
     Document, and any Warranty Disclaimers, provided that you also
     include the original English version of this License and the
     original versions of those notices and disclaimers.  In case of a
     disagreement between the translation and the original version of
     this License or a notice or disclaimer, the original version will
     prevail.

     If a section in the Document is Entitled "Acknowledgements",
     "Dedications", or "History", the requirement (section 4) to
     Preserve its Title (section 1) will typically require changing the
     actual title.

  9. TERMINATION

     You may not copy, modify, sublicense, or distribute the Document
     except as expressly provided for under this License.  Any other
     attempt to copy, modify, sublicense or distribute the Document is
     void, and will automatically terminate your rights under this
     License.  However, parties who have received copies, or rights,
     from you under this License will not have their licenses terminated
     so long as such parties remain in full compliance.

  10. FUTURE REVISIONS OF THIS LICENSE

     The Free Software Foundation may publish new, revised versions of
     the GNU Free Documentation License from time to time.  Such new
     versions will be similar in spirit to the present version, but may
     differ in detail to address new problems or concerns.  See
     <http://www.gnu.org/copyleft/>.

     Each version of the License is given a distinguishing version
     number.  If the Document specifies that a particular numbered
     version of this License "or any later version" applies to it, you
     have the option of following the terms and conditions either of
     that specified version or of any later version that has been
     published (not as a draft) by the Free Software Foundation.  If the
     Document does not specify a version number of this License, you may
     choose any version ever published (not as a draft) by the Free
     Software Foundation.

D.1.1 ADDENDUM: How to use this License for your documents
----------------------------------------------------------

To use this License in a document you have written, include a copy of
the License in the document and put the following copyright and license
notices just after the title page:

       Copyright (C)  YEAR  YOUR NAME.
       Permission is granted to copy, distribute and/or modify this document
       under the terms of the GNU Free Documentation License, Version 1.2
       or any later version published by the Free Software Foundation;
       with no Invariant Sections, no Front-Cover Texts, and no Back-Cover
       Texts.  A copy of the license is included in the section entitled ``GNU
       Free Documentation License''.

   If you have Invariant Sections, Front-Cover Texts and Back-Cover
Texts, replace the "with...Texts." line with this:

         with the Invariant Sections being LIST THEIR TITLES, with
         the Front-Cover Texts being LIST, and with the Back-Cover Texts
         being LIST.

   If you have Invariant Sections without Cover Texts, or some other
combination of the three, merge those two alternatives to suit the
situation.

   If your document contains nontrivial examples of program code, we
recommend releasing these examples in parallel under your choice of free
software license, such as the GNU General Public License, to permit
their use in free software.

D.2 GNU GENERAL PUBLIC LICENSE
==============================

                        Version 3, 29 June 2007

     Copyright © 2007 Free Software Foundation, Inc. <http://fsf.org/>

     Everyone is permitted to copy and distribute verbatim copies of this
     license document, but changing it is not allowed.

Preamble
========

The GNU General Public License is a free, copyleft license for software
and other kinds of works.

   The licenses for most software and other practical works are designed
to take away your freedom to share and change the works.  By contrast,
the GNU General Public License is intended to guarantee your freedom to
share and change all versions of a program---to make sure it remains free
software for all its users.  We, the Free Software Foundation, use the
GNU General Public License for most of our software; it applies also to
any other work released this way by its authors.  You can apply it to
your programs, too.

   When we speak of free software, we are referring to freedom, not
price.  Our General Public Licenses are designed to make sure that you
have the freedom to distribute copies of free software (and charge for
them if you wish), that you receive source code or can get it if you
want it, that you can change the software or use pieces of it in new
free programs, and that you know you can do these things.

   To protect your rights, we need to prevent others from denying you
these rights or asking you to surrender the rights.  Therefore, you have
certain responsibilities if you distribute copies of the software, or if
you modify it: responsibilities to respect the freedom of others.

   For example, if you distribute copies of such a program, whether
gratis or for a fee, you must pass on to the recipients the same
freedoms that you received.  You must make sure that they, too, receive
or can get the source code.  And you must show them these terms so they
know their rights.

   Developers that use the GNU GPL protect your rights with two steps:
(1) assert copyright on the software, and (2) offer you this License
giving you legal permission to copy, distribute and/or modify it.

   For the developers' and authors' protection, the GPL clearly explains
that there is no warranty for this free software.  For both users' and
authors' sake, the GPL requires that modified versions be marked as
changed, so that their problems will not be attributed erroneously to
authors of previous versions.

   Some devices are designed to deny users access to install or run
modified versions of the software inside them, although the manufacturer
can do so.  This is fundamentally incompatible with the aim of
protecting users' freedom to change the software.  The systematic
pattern of such abuse occurs in the area of products for individuals to
use, which is precisely where it is most unacceptable.  Therefore, we
have designed this version of the GPL to prohibit the practice for those
products.  If such problems arise substantially in other domains, we
stand ready to extend this provision to those domains in future versions
of the GPL, as needed to protect the freedom of users.

   Finally, every program is threatened constantly by software patents.
States should not allow patents to restrict development and use of
software on general-purpose computers, but in those that do, we wish to
avoid the special danger that patents applied to a free program could
make it effectively proprietary.  To prevent this, the GPL assures that
patents cannot be used to render the program non-free.

   The precise terms and conditions for copying, distribution and
modification follow.

TERMS AND CONDITIONS
====================

  0. Definitions.

     "This License" refers to version 3 of the GNU General Public
     License.

     "Copyright" also means copyright-like laws that apply to other
     kinds of works, such as semiconductor masks.

     "The Program" refers to any copyrightable work licensed under this
     License.  Each licensee is addressed as "you".  "Licensees" and
     "recipients" may be individuals or organizations.

     To "modify" a work means to copy from or adapt all or part of the
     work in a fashion requiring copyright permission, other than the
     making of an exact copy.  The resulting work is called a "modified
     version" of the earlier work or a work "based on" the earlier work.

     A "covered work" means either the unmodified Program or a work
     based on the Program.

     To "propagate" a work means to do anything with it that, without
     permission, would make you directly or secondarily liable for
     infringement under applicable copyright law, except executing it on
     a computer or modifying a private copy.  Propagation includes
     copying, distribution (with or without modification), making
     available to the public, and in some countries other activities as
     well.

     To "convey" a work means any kind of propagation that enables other
     parties to make or receive copies.  Mere interaction with a user
     through a computer network, with no transfer of a copy, is not
     conveying.

     An interactive user interface displays "Appropriate Legal Notices"
     to the extent that it includes a convenient and prominently visible
     feature that (1) displays an appropriate copyright notice, and (2)
     tells the user that there is no warranty for the work (except to
     the extent that warranties are provided), that licensees may convey
     the work under this License, and how to view a copy of this
     License.  If the interface presents a list of user commands or
     options, such as a menu, a prominent item in the list meets this
     criterion.

  1. Source Code.

     The "source code" for a work means the preferred form of the work
     for making modifications to it.  "Object code" means any non-source
     form of a work.

     A "Standard Interface" means an interface that either is an
     official standard defined by a recognized standards body, or, in
     the case of interfaces specified for a particular programming
     language, one that is widely used among developers working in that
     language.

     The "System Libraries" of an executable work include anything,
     other than the work as a whole, that (a) is included in the normal
     form of packaging a Major Component, but which is not part of that
     Major Component, and (b) serves only to enable use of the work with
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     which an implementation is available to the public in source code
     form.  A "Major Component", in this context, means a major
     essential component (kernel, window system, and so on) of the
     specific operating system (if any) on which the executable work
     runs, or a compiler used to produce the work, or an object code
     interpreter used to run it.

     The "Corresponding Source" for a work in object code form means all
     the source code needed to generate, install, and (for an executable
     work) run the object code and to modify the work, including scripts
     to control those activities.  However, it does not include the
     work's System Libraries, or general-purpose tools or generally
     available free programs which are used unmodified in performing
     those activities but which are not part of the work.  For example,
     Corresponding Source includes interface definition files associated
     with source files for the work, and the source code for shared
     libraries and dynamically linked subprograms that the work is
     specifically designed to require, such as by intimate data
     communication or control flow between those subprograms and other
     parts of the work.

     The Corresponding Source need not include anything that users can
     regenerate automatically from other parts of the Corresponding
     Source.

     The Corresponding Source for a work in source code form is that
     same work.

  2. Basic Permissions.

     All rights granted under this License are granted for the term of
     copyright on the Program, and are irrevocable provided the stated
     conditions are met.  This License explicitly affirms your unlimited
     permission to run the unmodified Program.  The output from running
     a covered work is covered by this License only if the output, given
     its content, constitutes a covered work.  This License acknowledges
     your rights of fair use or other equivalent, as provided by
     copyright law.

     You may make, run and propagate covered works that you do not
     convey, without conditions so long as your license otherwise
     remains in force.  You may convey covered works to others for the
     sole purpose of having them make modifications exclusively for you,
     or provide you with facilities for running those works, provided
     that you comply with the terms of this License in conveying all
     material for which you do not control copyright.  Those thus making
     or running the covered works for you must do so exclusively on your
     behalf, under your direction and control, on terms that prohibit
     them from making any copies of your copyrighted material outside
     their relationship with you.

     Conveying under any other circumstances is permitted solely under
     the conditions stated below.  Sublicensing is not allowed; section
     10 makes it unnecessary.

  3. Protecting Users' Legal Rights From Anti-Circumvention Law.

     No covered work shall be deemed part of an effective technological
     measure under any applicable law fulfilling obligations under
     article 11 of the WIPO copyright treaty adopted on 20 December
     1996, or similar laws prohibiting or restricting circumvention of
     such measures.

     When you convey a covered work, you waive any legal power to forbid
     circumvention of technological measures to the extent such
     circumvention is effected by exercising rights under this License
     with respect to the covered work, and you disclaim any intention to
     limit operation or modification of the work as a means of
     enforcing, against the work's users, your or third parties' legal
     rights to forbid circumvention of technological measures.

  4. Conveying Verbatim Copies.

     You may convey verbatim copies of the Program's source code as you
     receive it, in any medium, provided that you conspicuously and
     appropriately publish on each copy an appropriate copyright notice;
     keep intact all notices stating that this License and any
     non-permissive terms added in accord with section 7 apply to the
     code; keep intact all notices of the absence of any warranty; and
     give all recipients a copy of this License along with the Program.

     You may charge any price or no price for each copy that you convey,
     and you may offer support or warranty protection for a fee.

  5. Conveying Modified Source Versions.

     You may convey a work based on the Program, or the modifications to
     produce it from the Program, in the form of source code under the
     terms of section 4, provided that you also meet all of these
     conditions:

       a. The work must carry prominent notices stating that you
          modified it, and giving a relevant date.

       b. The work must carry prominent notices stating that it is
          released under this License and any conditions added under
          section 7.  This requirement modifies the requirement in
          section 4 to "keep intact all notices".

       c. You must license the entire work, as a whole, under this
          License to anyone who comes into possession of a copy.  This
          License will therefore apply, along with any applicable
          section 7 additional terms, to the whole of the work, and all
          its parts, regardless of how they are packaged.  This License
          gives no permission to license the work in any other way, but
          it does not invalidate such permission if you have separately
          received it.

       d. If the work has interactive user interfaces, each must display
          Appropriate Legal Notices; however, if the Program has
          interactive interfaces that do not display Appropriate Legal
          Notices, your work need not make them do so.

     A compilation of a covered work with other separate and independent
     works, which are not by their nature extensions of the covered
     work, and which are not combined with it such as to form a larger
     program, in or on a volume of a storage or distribution medium, is
     called an "aggregate" if the compilation and its resulting
     copyright are not used to limit the access or legal rights of the
     compilation's users beyond what the individual works permit.
     Inclusion of a covered work in an aggregate does not cause this
     License to apply to the other parts of the aggregate.

  6. Conveying Non-Source Forms.

     You may convey a covered work in object code form under the terms
     of sections 4 and 5, provided that you also convey the
     machine-readable Corresponding Source under the terms of this
     License, in one of these ways:

       a. Convey the object code in, or embodied in, a physical product
          (including a physical distribution medium), accompanied by the
          Corresponding Source fixed on a durable physical medium
          customarily used for software interchange.

       b. Convey the object code in, or embodied in, a physical product
          (including a physical distribution medium), accompanied by a
          written offer, valid for at least three years and valid for as
          long as you offer spare parts or customer support for that
          product model, to give anyone who possesses the object code
          either (1) a copy of the Corresponding Source for all the
          software in the product that is covered by this License, on a
          durable physical medium customarily used for software
          interchange, for a price no more than your reasonable cost of
          physically performing this conveying of source, or (2) access
          to copy the Corresponding Source from a network server at no
          charge.

       c. Convey individual copies of the object code with a copy of the
          written offer to provide the Corresponding Source.  This
          alternative is allowed only occasionally and noncommercially,
          and only if you received the object code with such an offer,
          in accord with subsection 6b.

       d. Convey the object code by offering access from a designated
          place (gratis or for a charge), and offer equivalent access to
          the Corresponding Source in the same way through the same
          place at no further charge.  You need not require recipients
          to copy the Corresponding Source along with the object code.
          If the place to copy the object code is a network server, the
          Corresponding Source may be on a different server (operated by
          you or a third party) that supports equivalent copying
          facilities, provided you maintain clear directions next to the
          object code saying where to find the Corresponding Source.
          Regardless of what server hosts the Corresponding Source, you
          remain obligated to ensure that it is available for as long as
          needed to satisfy these requirements.

       e. Convey the object code using peer-to-peer transmission,
          provided you inform other peers where the object code and
          Corresponding Source of the work are being offered to the
          general public at no charge under subsection 6d.

     A separable portion of the object code, whose source code is
     excluded from the Corresponding Source as a System Library, need
     not be included in conveying the object code work.

     A "User Product" is either (1) a "consumer product", which means
     any tangible personal property which is normally used for personal,
     family, or household purposes, or (2) anything designed or sold for
     incorporation into a dwelling.  In determining whether a product is
     a consumer product, doubtful cases shall be resolved in favor of
     coverage.  For a particular product received by a particular user,
     "normally used" refers to a typical or common use of that class of
     product, regardless of the status of the particular user or of the
     way in which the particular user actually uses, or expects or is
     expected to use, the product.  A product is a consumer product
     regardless of whether the product has substantial commercial,
     industrial or non-consumer uses, unless such uses represent the
     only significant mode of use of the product.

     "Installation Information" for a User Product means any methods,
     procedures, authorization keys, or other information required to
     install and execute modified versions of a covered work in that
     User Product from a modified version of its Corresponding Source.
     The information must suffice to ensure that the continued
     functioning of the modified object code is in no case prevented or
     interfered with solely because modification has been made.

     If you convey an object code work under this section in, or with,
     or specifically for use in, a User Product, and the conveying
     occurs as part of a transaction in which the right of possession
     and use of the User Product is transferred to the recipient in
     perpetuity or for a fixed term (regardless of how the transaction
     is characterized), the Corresponding Source conveyed under this
     section must be accompanied by the Installation Information.  But
     this requirement does not apply if neither you nor any third party
     retains the ability to install modified object code on the User
     Product (for example, the work has been installed in ROM).

     The requirement to provide Installation Information does not
     include a requirement to continue to provide support service,
     warranty, or updates for a work that has been modified or installed
     by the recipient, or for the User Product in which it has been
     modified or installed.  Access to a network may be denied when the
     modification itself materially and adversely affects the operation
     of the network or violates the rules and protocols for
     communication across the network.

     Corresponding Source conveyed, and Installation Information
     provided, in accord with this section must be in a format that is
     publicly documented (and with an implementation available to the
     public in source code form), and must require no special password
     or key for unpacking, reading or copying.

  7. Additional Terms.

     "Additional permissions" are terms that supplement the terms of
     this License by making exceptions from one or more of its
     conditions.  Additional permissions that are applicable to the
     entire Program shall be treated as though they were included in
     this License, to the extent that they are valid under applicable
     law.  If additional permissions apply only to part of the Program,
     that part may be used separately under those permissions, but the
     entire Program remains governed by this License without regard to
     the additional permissions.

     When you convey a copy of a covered work, you may at your option
     remove any additional permissions from that copy, or from any part
     of it.  (Additional permissions may be written to require their own
     removal in certain cases when you modify the work.)  You may place
     additional permissions on material, added by you to a covered work,
     for which you have or can give appropriate copyright permission.

     Notwithstanding any other provision of this License, for material
     you add to a covered work, you may (if authorized by the copyright
     holders of that material) supplement the terms of this License with
     terms:

       a. Disclaiming warranty or limiting liability differently from
          the terms of sections 15 and 16 of this License; or

       b. Requiring preservation of specified reasonable legal notices
          or author attributions in that material or in the Appropriate
          Legal Notices displayed by works containing it; or

       c. Prohibiting misrepresentation of the origin of that material,
          or requiring that modified versions of such material be marked
          in reasonable ways as different from the original version; or

       d. Limiting the use for publicity purposes of names of licensors
          or authors of the material; or

       e. Declining to grant rights under trademark law for use of some
          trade names, trademarks, or service marks; or

       f. Requiring indemnification of licensors and authors of that
          material by anyone who conveys the material (or modified
          versions of it) with contractual assumptions of liability to
          the recipient, for any liability that these contractual
          assumptions directly impose on those licensors and authors.

     All other non-permissive additional terms are considered "further
     restrictions" within the meaning of section 10.  If the Program as
     you received it, or any part of it, contains a notice stating that
     it is governed by this License along with a term that is a further
     restriction, you may remove that term.  If a license document
     contains a further restriction but permits relicensing or conveying
     under this License, you may add to a covered work material governed
     by the terms of that license document, provided that the further
     restriction does not survive such relicensing or conveying.

     If you add terms to a covered work in accord with this section, you
     must place, in the relevant source files, a statement of the
     additional terms that apply to those files, or a notice indicating
     where to find the applicable terms.

     Additional terms, permissive or non-permissive, may be stated in
     the form of a separately written license, or stated as exceptions;
     the above requirements apply either way.

  8. Termination.

     You may not propagate or modify a covered work except as expressly
     provided under this License.  Any attempt otherwise to propagate or
     modify it is void, and will automatically terminate your rights
     under this License (including any patent licenses granted under the
     third paragraph of section 11).

     However, if you cease all violation of this License, then your
     license from a particular copyright holder is reinstated (a)
     provisionally, unless and until the copyright holder explicitly and
     finally terminates your license, and (b) permanently, if the
     copyright holder fails to notify you of the violation by some
     reasonable means prior to 60 days after the cessation.

     Moreover, your license from a particular copyright holder is
     reinstated permanently if the copyright holder notifies you of the
     violation by some reasonable means, this is the first time you have
     received notice of violation of this License (for any work) from
     that copyright holder, and you cure the violation prior to 30 days
     after your receipt of the notice.

     Termination of your rights under this section does not terminate
     the licenses of parties who have received copies or rights from you
     under this License.  If your rights have been terminated and not
     permanently reinstated, you do not qualify to receive new licenses
     for the same material under section 10.

  9. Acceptance Not Required for Having Copies.

     You are not required to accept this License in order to receive or
     run a copy of the Program.  Ancillary propagation of a covered work
     occurring solely as a consequence of using peer-to-peer
     transmission to receive a copy likewise does not require
     acceptance.  However, nothing other than this License grants you
     permission to propagate or modify any covered work.  These actions
     infringe copyright if you do not accept this License.  Therefore,
     by modifying or propagating a covered work, you indicate your
     acceptance of this License to do so.

  10. Automatic Licensing of Downstream Recipients.

     Each time you convey a covered work, the recipient automatically
     receives a license from the original licensors, to run, modify and
     propagate that work, subject to this License.  You are not
     responsible for enforcing compliance by third parties with this
     License.

     An "entity transaction" is a transaction transferring control of an
     organization, or substantially all assets of one, or subdividing an
     organization, or merging organizations.  If propagation of a
     covered work results from an entity transaction, each party to that
     transaction who receives a copy of the work also receives whatever
     licenses to the work the party's predecessor in interest had or
     could give under the previous paragraph, plus a right to possession
     of the Corresponding Source of the work from the predecessor in
     interest, if the predecessor has it or can get it with reasonable
     efforts.

     You may not impose any further restrictions on the exercise of the
     rights granted or affirmed under this License.  For example, you
     may not impose a license fee, royalty, or other charge for exercise
     of rights granted under this License, and you may not initiate
     litigation (including a cross-claim or counterclaim in a lawsuit)
     alleging that any patent claim is infringed by making, using,
     selling, offering for sale, or importing the Program or any portion
     of it.

  11. Patents.

     A "contributor" is a copyright holder who authorizes use under this
     License of the Program or a work on which the Program is based.
     The work thus licensed is called the contributor's "contributor
     version".

     A contributor's "essential patent claims" are all patent claims
     owned or controlled by the contributor, whether already acquired or
     hereafter acquired, that would be infringed by some manner,
     permitted by this License, of making, using, or selling its
     contributor version, but do not include claims that would be
     infringed only as a consequence of further modification of the
     contributor version.  For purposes of this definition, "control"
     includes the right to grant patent sublicenses in a manner
     consistent with the requirements of this License.

     Each contributor grants you a non-exclusive, worldwide,
     royalty-free patent license under the contributor's essential
     patent claims, to make, use, sell, offer for sale, import and
     otherwise run, modify and propagate the contents of its contributor
     version.

     In the following three paragraphs, a "patent license" is any
     express agreement or commitment, however denominated, not to
     enforce a patent (such as an express permission to practice a
     patent or covenant not to sue for patent infringement).  To "grant"
     such a patent license to a party means to make such an agreement or
     commitment not to enforce a patent against the party.

     If you convey a covered work, knowingly relying on a patent
     license, and the Corresponding Source of the work is not available
     for anyone to copy, free of charge and under the terms of this
     License, through a publicly available network server or other
     readily accessible means, then you must either (1) cause the
     Corresponding Source to be so available, or (2) arrange to deprive
     yourself of the benefit of the patent license for this particular
     work, or (3) arrange, in a manner consistent with the requirements
     of this License, to extend the patent license to downstream
     recipients.  "Knowingly relying" means you have actual knowledge
     that, but for the patent license, your conveying the covered work
     in a country, or your recipient's use of the covered work in a
     country, would infringe one or more identifiable patents in that
     country that you have reason to believe are valid.

     If, pursuant to or in connection with a single transaction or
     arrangement, you convey, or propagate by procuring conveyance of, a
     covered work, and grant a patent license to some of the parties
     receiving the covered work authorizing them to use, propagate,
     modify or convey a specific copy of the covered work, then the
     patent license you grant is automatically extended to all
     recipients of the covered work and works based on it.

     A patent license is "discriminatory" if it does not include within
     the scope of its coverage, prohibits the exercise of, or is
     conditioned on the non-exercise of one or more of the rights that
     are specifically granted under this License.  You may not convey a
     covered work if you are a party to an arrangement with a third
     party that is in the business of distributing software, under which
     you make payment to the third party based on the extent of your
     activity of conveying the work, and under which the third party
     grants, to any of the parties who would receive the covered work
     from you, a discriminatory patent license (a) in connection with
     copies of the covered work conveyed by you (or copies made from
     those copies), or (b) primarily for and in connection with specific
     products or compilations that contain the covered work, unless you
     entered into that arrangement, or that patent license was granted,
     prior to 28 March 2007.

     Nothing in this License shall be construed as excluding or limiting
     any implied license or other defenses to infringement that may
     otherwise be available to you under applicable patent law.

  12. No Surrender of Others' Freedom.

     If conditions are imposed on you (whether by court order, agreement
     or otherwise) that contradict the conditions of this License, they
     do not excuse you from the conditions of this License.  If you
     cannot convey a covered work so as to satisfy simultaneously your
     obligations under this License and any other pertinent obligations,
     then as a consequence you may not convey it at all.  For example,
     if you agree to terms that obligate you to collect a royalty for
     further conveying from those to whom you convey the Program, the
     only way you could satisfy both those terms and this License would
     be to refrain entirely from conveying the Program.

  13. Use with the GNU Affero General Public License.

     Notwithstanding any other provision of this License, you have
     permission to link or combine any covered work with a work licensed
     under version 3 of the GNU Affero General Public License into a
     single combined work, and to convey the resulting work.  The terms
     of this License will continue to apply to the part which is the
     covered work, but the special requirements of the GNU Affero
     General Public License, section 13, concerning interaction through
     a network will apply to the combination as such.

  14. Revised Versions of this License.

     The Free Software Foundation may publish revised and/or new
     versions of the GNU General Public License from time to time.  Such
     new versions will be similar in spirit to the present version, but
     may differ in detail to address new problems or concerns.

     Each version is given a distinguishing version number.  If the
     Program specifies that a certain numbered version of the GNU
     General Public License "or any later version" applies to it, you
     have the option of following the terms and conditions either of
     that numbered version or of any later version published by the Free
     Software Foundation.  If the Program does not specify a version
     number of the GNU General Public License, you may choose any
     version ever published by the Free Software Foundation.

     If the Program specifies that a proxy can decide which future
     versions of the GNU General Public License can be used, that
     proxy's public statement of acceptance of a version permanently
     authorizes you to choose that version for the Program.

     Later license versions may give you additional or different
     permissions.  However, no additional obligations are imposed on any
     author or copyright holder as a result of your choosing to follow a
     later version.

  15. Disclaimer of Warranty.

     THERE IS NO WARRANTY FOR THE PROGRAM, TO THE EXTENT PERMITTED BY
     APPLICABLE LAW. EXCEPT WHEN OTHERWISE STATED IN WRITING THE
     COPYRIGHT HOLDERS AND/OR OTHER PARTIES PROVIDE THE PROGRAM "AS IS"
     WITHOUT WARRANTY OF ANY KIND, EITHER EXPRESSED OR IMPLIED,
     INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF
     MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE. THE ENTIRE
     RISK AS TO THE QUALITY AND PERFORMANCE OF THE PROGRAM IS WITH YOU.
     SHOULD THE PROGRAM PROVE DEFECTIVE, YOU ASSUME THE COST OF ALL
     NECESSARY SERVICING, REPAIR OR CORRECTION.

  16. Limitation of Liability.

     IN NO EVENT UNLESS REQUIRED BY APPLICABLE LAW OR AGREED TO IN
     WRITING WILL ANY COPYRIGHT HOLDER, OR ANY OTHER PARTY WHO MODIFIES
     AND/OR CONVEYS THE PROGRAM AS PERMITTED ABOVE, BE LIABLE TO YOU FOR
     DAMAGES, INCLUDING ANY GENERAL, SPECIAL, INCIDENTAL OR
     CONSEQUENTIAL DAMAGES ARISING OUT OF THE USE OR INABILITY TO USE
     THE PROGRAM (INCLUDING BUT NOT LIMITED TO LOSS OF DATA OR DATA
     BEING RENDERED INACCURATE OR LOSSES SUSTAINED BY YOU OR THIRD
     PARTIES OR A FAILURE OF THE PROGRAM TO OPERATE WITH ANY OTHER
     PROGRAMS), EVEN IF SUCH HOLDER OR OTHER PARTY HAS BEEN ADVISED OF
     THE POSSIBILITY OF SUCH DAMAGES.

  17. Interpretation of Sections 15 and 16.

     If the disclaimer of warranty and limitation of liability provided
     above cannot be given local legal effect according to their terms,
     reviewing courts shall apply local law that most closely
     approximates an absolute waiver of all civil liability in
     connection with the Program, unless a warranty or assumption of
     liability accompanies a copy of the Program in return for a fee.

END OF TERMS AND CONDITIONS
===========================

How to Apply These Terms to Your New Programs
=============================================

If you develop a new program, and you want it to be of the greatest
possible use to the public, the best way to achieve this is to make it
free software which everyone can redistribute and change under these
terms.

   To do so, attach the following notices to the program.  It is safest
to attach them to the start of each source file to most effectively
state the exclusion of warranty; and each file should have at least the
"copyright" line and a pointer to where the full notice is found.

     ONE LINE TO GIVE THE PROGRAM'S NAME AND A BRIEF IDEA OF WHAT IT DOES.
     Copyright (C) YEAR NAME OF AUTHOR

     This program is free software: you can redistribute it and/or modify
     it under the terms of the GNU General Public License as published by
     the Free Software Foundation, either version 3 of the License, or (at
     your option) any later version.

     This program is distributed in the hope that it will be useful, but
     WITHOUT ANY WARRANTY; without even the implied warranty of
     MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
     General Public License for more details.

     You should have received a copy of the GNU General Public License
     along with this program.  If not, see <http://www.gnu.org/licenses/>.

   Also add information on how to contact you by electronic and paper
mail.

   If the program does terminal interaction, make it output a short
notice like this when it starts in an interactive mode:

     PROGRAM Copyright (C) YEAR NAME OF AUTHOR
     This program comes with ABSOLUTELY NO WARRANTY; for details type 'show w'.
     This is free software, and you are welcome to redistribute it
     under certain conditions; type 'show c' for details.

   The hypothetical commands 'show w' and 'show c' should show the
appropriate parts of the General Public License.  Of course, your
program's commands might be different; for a GUI interface, you would
use an "about box".

   You should also get your employer (if you work as a programmer) or
school, if any, to sign a "copyright disclaimer" for the program, if
necessary.  For more information on this, and how to apply and follow
the GNU GPL, see <http://www.gnu.org/licenses/>.

   The GNU General Public License does not permit incorporating your
program into proprietary programs.  If your program is a subroutine
library, you may consider it more useful to permit linking proprietary
applications with the library.  If this is what you want to do, use the
GNU Lesser General Public License instead of this License.  But first,
please read <http://www.gnu.org/philosophy/why-not-lgpl.html>.

Word Index
**********

This index is a list of Forth words that have "glossary" entries within
this manual.  Each word is listed with its stack effect and wordset.

* Menu:

* ! ( W A-ADDR -- ) core:                Memory Access.     (line  4877)
* !!FIXME!! ( -- ) gforth-1.0:           Debugging.         (line 14380)
* !@ ( U1 A-ADDR -- U2 ) gforth-experimental: Hardware operations for multi-tasking.
                                                            (line 14814)
* !resize ( RX RY RW RH RD -- ) minos2:  widget methods.    (line 19175)
* !size ( -- ) minos2:                   widget methods.    (line 19178)
* # ( UD1 -- UD2 ) core:                 Formatted numeric output.
                                                            (line 10506)
* #! ( -- ) gforth-0.2:                  Running Image Files.
                                                            (line 18288)
* #> ( XD -- ADDR U ) core:              Formatted numeric output.
                                                            (line 10529)
* #>> ( -- ) gforth-0.5:                 Formatted numeric output.
                                                            (line 10536)
* #bell ( -- C ) gforth-0.2:             String and character literals.
                                                            (line  5389)
* #bs ( -- C ) gforth-0.2:               String and character literals.
                                                            (line  5385)
* #cr ( -- C ) gforth-0.2:               String and character literals.
                                                            (line  5381)
* #del ( -- C ) gforth-0.2:              String and character literals.
                                                            (line  5387)
* #eof ( -- C ) gforth-0.7:              String and character literals.
                                                            (line  5393)
* #esc ( -- C ) gforth-0.5:              String and character literals.
                                                            (line  5391)
* #ff ( -- C ) gforth-0.2:               String and character literals.
                                                            (line  5383)
* #lf ( -- C ) gforth-0.2:               String and character literals.
                                                            (line  5379)
* #line ( "U" "["FILE"]" -- ) gforth-1.0: Interpreter Directives.
                                                            (line  9000)
* #loc ( NLINE NCHAR "FILE" -- ) gforth-1.0: Debugging.     (line 14398)
* #locals ( -- N ) environment:          Environmental Queries.
                                                            (line  9660)
* #s ( UD -- 0 0 ) core:                 Formatted numeric output.
                                                            (line 10511)
* #tab ( -- C ) gforth-0.2:              String and character literals.
                                                            (line  5377)
* #tib ( -- ADDR ) core-ext-obsolescent: The Text Interpreter.
                                                            (line  8761)
* $! ( ADDR1 U $ADDR -- ) gforth-0.7:    $tring words.      (line  5517)
* $!len ( U $ADDR -- ) gforth-0.7:       $tring words.      (line  5527)
* $+! ( ADDR1 U $ADDR -- ) gforth-0.7:   $tring words.      (line  5541)
* $+!len ( U $ADDR -- ADDR ) gforth-1.0: $tring words.      (line  5531)
* $+slurp ( FID ADDR -- ) gforth-1.0:    $tring words.      (line  5582)
* $+slurp-file ( C-ADDR U ADDR -- ) gforth-1.0: $tring words.
                                                            (line  5586)
* $+[]! ( C-ADDR U $[]ADDR -- ) gforth-1.0: $tring words.   (line  5601)
* $. ( ADDR -- ) gforth-1.0:             $tring words.      (line  5572)
* $? ( -- N ) gforth-0.2:                Passing Commands to the OS.
                                                            (line 16545)
* $@ ( $ADDR -- ADDR2 U ) gforth-0.7:    $tring words.      (line  5521)
* $@len ( $ADDR -- U ) gforth-0.7:       $tring words.      (line  5524)
* $boot ( $ADDR -- ) gforth-1.0:         $tring words.      (line  5636)
* $del ( ADDR OFF U -- ) gforth-0.7:     $tring words.      (line  5535)
* $exec ( XT ADDR -- ) gforth-1.0:       $tring words.      (line  5565)
* $free ( $ADDR -- ) gforth-1.0:         $tring words.      (line  5547)
* $init ( $ADDR -- ) gforth-1.0:         $tring words.      (line  5550)
* $ins ( ADDR1 U $ADDR OFF -- ) gforth-0.7: $tring words.   (line  5538)
* $iter ( .. $ADDR CHAR XT -- .. ) gforth-0.7: $tring words.
                                                            (line  5557)
* $over ( ADDR U $ADDR OFF -- ) gforth-1.0: $tring words.   (line  5562)
* $save ( $ADDR -- ) gforth-1.0:         $tring words.      (line  5630)
* $saved ( ADDR -- ) gforth-1.0:         $tring words.      (line  5643)
* $slurp ( FID ADDR -- ) gforth-1.0:     $tring words.      (line  5575)
* $slurp-file ( C-ADDR U ADDR -- ) gforth-1.0: $tring words.
                                                            (line  5579)
* $split ( ADDR U CHAR -- ADDR1 U1 ADDR2 U2 ) gforth-0.7: $tring words.
                                                            (line  5553)
* $substitute ( ADDR1 LEN1 -- ADDR2 LEN2 N/IOR ) gforth-experimental: Substitute.
                                                            (line 11363)
* $tmp ( XT -- ADDR U ) gforth-1.0:      $tring words.      (line  5569)
* $unescape ( ADDR1 U1 -- ADDR2 U2 ) gforth-experimental: Substitute.
                                                            (line 11378)
* $Variable ( -- ) gforth-1.0:           $tring words.      (line  5649)
* $[] ( U $[]ADDR -- ADDR' ) gforth-1.0: $tring words.      (line  5589)
* $[]! ( C-ADDR U N $[]ADDR -- ) gforth-1.0: $tring words.  (line  5593)
* $[]# ( ADDR -- LEN ) gforth-1.0:       $tring words.      (line  5609)
* $[]+! ( C-ADDR U N $[]ADDR -- ) gforth-1.0: $tring words. (line  5597)
* $[]. ( ADDR -- ) gforth-1.0:           $tring words.      (line  5622)
* $[]@ ( N $[]ADDR -- ADDR U ) gforth-1.0: $tring words.    (line  5605)
* $[]boot ( ADDR -- ) gforth-1.0:        $tring words.      (line  5640)
* $[]free ( ADDR -- ) gforth-1.0:        $tring words.      (line  5625)
* $[]map ( ADDR XT -- ) gforth-1.0:      $tring words.      (line  5612)
* $[]save ( ADDR -- ) gforth-1.0:        $tring words.      (line  5633)
* $[]saved ( ADDR -- ) gforth-1.0:       $tring words.      (line  5646)
* $[]slurp ( FID ADDR -- ) gforth-1.0:   $tring words.      (line  5616)
* $[]slurp-file ( ADDR U $ADDR -- ) gforth-1.0: $tring words.
                                                            (line  5619)
* $[]Variable ( -- ) gforth-1.0:         $tring words.      (line  5652)
* %align ( ALIGN SIZE -- ) gforth-0.4:   Structure Glossary.
                                                            (line 12397)
* %alignment ( ALIGN SIZE -- ALIGN ) gforth-0.4: Structure Glossary.
                                                            (line 12400)
* %alloc ( ALIGN SIZE -- ADDR ) gforth-0.4: Structure Glossary.
                                                            (line 12403)
* %allocate ( ALIGN SIZE -- ADDR IOR ) gforth-0.4: Structure Glossary.
                                                            (line 12407)
* %allot ( ALIGN SIZE -- ADDR ) gforth-0.4: Structure Glossary.
                                                            (line 12411)
* %size ( ALIGN SIZE -- SIZE ) gforth-0.4: Structure Glossary.
                                                            (line 12439)
* ' ( "NAME" -- XT ) core:               Execution token.   (line  8106)
* 'cold ( -- ) gforth-0.2:               Modifying the Startup Sequence.
                                                            (line 18344)
* 's ( ADDR1 TASK -- ADDR2 ) gforth-experimental: Task-local data.
                                                            (line 14769)
* ( ( COMPILATION 'CCC<CLOSE-PAREN>' -- ; RUN-TIME -- ) core,file: Comments.
                                                            (line  3737)
* (( ( ADDR U -- ) regexp-pattern:       Regular Expressions.
                                                            (line 13806)
* (local) ( ADDR U -- ) local:           Standard Forth locals.
                                                            (line 12159)
* (to) ( VAL OPERATION XT -- ) gforth-1.0: User-defined TO and DEFER@.
                                                            (line  7521)
* ) ( -- ) gforth-0.2:                   Assertions.        (line 14444)
* )) ( -- FLAG ) regexp-pattern:         Regular Expressions.
                                                            (line 13809)
* * ( N1 N2 -- N ) core:                 Single precision.  (line  3811)
* **} ( SYS -- ) regexp-pattern:         Regular Expressions.
                                                            (line 13891)
* */ ( ( N1 N2 N3 -- N4 ) core:          Integer division.  (line  3956)
* */f ( N1 N2 N3 -- N4 ) gforth-1.0:     Integer division.  (line  3962)
* */mod ( N1 N2 N3 -- N4 N5 ) core:      Integer division.  (line  3968)
* */modf ( N1 N2 N3 -- N4 N5 ) gforth-1.0: Integer division.
                                                            (line  3976)
* */mods ( N1 N2 N3 -- N4 N5 ) gforth-1.0: Integer division.
                                                            (line  3972)
* */s ( N1 N2 N3 -- N4 ) gforth-1.0:     Integer division.  (line  3959)
* *align ( N -- ) gforth-1.0:            Address arithmetic.
                                                            (line  5153)
* *aligned ( ADDR1 N -- ADDR2 ) gforth-1.0: Address arithmetic.
                                                            (line  5149)
* *} ( ADDR ADDR' -- ADDR' ) regexp-pattern: Regular Expressions.
                                                            (line 13903)
* + ( N1 N2 -- N ) core:                 Single precision.  (line  3800)
* +! ( N A-ADDR -- ) core:               Memory Access.     (line  4880)
* +!@ ( U1 A-ADDR -- U2 ) gforth-experimental: Hardware operations for multi-tasking.
                                                            (line 14817)
* ++} ( SYS -- ) regexp-pattern:         Regular Expressions.
                                                            (line 13897)
* +char ( CHAR -- ) regexp-cg:           Regular Expressions.
                                                            (line 13820)
* +chars ( ADDR U -- ) regexp-cg:        Regular Expressions.
                                                            (line 13829)
* +class ( CLASS -- ) regexp-cg:         Regular Expressions.
                                                            (line 13832)
* +DO ( COMPILATION -- DO-SYS ; RUN-TIME N1 N2 -- | LOOP-SYS ) gforth-0.2: Counted Loops.
                                                            (line  5987)
* +field ( NOFFSET1 NSIZE "NAME" -- NOFFSET2 ) facility-ext: Forth200x Structures.
                                                            (line 12491)
* +fmode ( FAM1 RWXRWXRWX -- FAM2 ) gforth-1.0: General files.
                                                            (line  9905)
* +load ( I*X N -- J*X ) gforth-0.2:     Blocks.            (line 10375)
* +LOOP ( COMPILATION DO-SYS -- ; RUN-TIME LOOP-SYS1 N -- | LOOP-SYS2 ) core: Counted Loops.
                                                            (line  6034)
* +ltrace ( -- ) gforth-1.0:             Debugging.         (line 14392)
* +thru ( I*X N1 N2 -- J*X ) gforth-0.2: Blocks.            (line 10379)
* +TO ( VALUE "NAME" -- ) gforth-1.0:    Values.            (line  6896)
* +x/string ( XC-ADDR1 U1 -- XC-ADDR2 U2 ) xchar-ext: Xchars and Unicode.
                                                            (line 11240)
* +} ( ADDR ADDR' -- ADDR' ) regexp-pattern: Regular Expressions.
                                                            (line 13909)
* , ( W -- ) core:                       Dictionary allocation.
                                                            (line  4738)
* - ( N1 N2 -- N ) core:                 Single precision.  (line  3807)
* -- ( HMADDR U LATEST LATESTNT WID 0 ... -- ) gforth-0.2: Locals definition words.
                                                            (line 11599)
* --> ( -- ) gforth-0.2:                 Blocks.            (line 10383)
* ->here ( ADDR -- ) gforth-1.0:         Dictionary allocation.
                                                            (line  4728)
* -c? ( ADDR CLASS -- ) regexp-pattern:  Regular Expressions.
                                                            (line 13845)
* -char ( CHAR -- ) regexp-cg:           Regular Expressions.
                                                            (line 13823)
* -class ( CLASS -- ) regexp-cg:         Regular Expressions.
                                                            (line 13835)
* -DO ( COMPILATION -- DO-SYS ; RUN-TIME N1 N2 -- | LOOP-SYS ) gforth-0.2: Counted Loops.
                                                            (line  6008)
* -infinity ( -- R ) gforth-1.0:         Floating Point.    (line  4490)
* -LOOP ( COMPILATION DO-SYS -- ; RUN-TIME LOOP-SYS1 U -- | LOOP-SYS2 ) gforth-0.2: Counted Loops.
                                                            (line  6037)
* -ltrace ( -- ) gforth-1.0:             Debugging.         (line 14395)
* -rot ( W1 W2 W3 -- W3 W1 W2 ) gforth-0.2: Data stack.     (line  4541)
* -trailing ( C_ADDR U1 -- C_ADDR U2 ) string: String words.
                                                            (line  5434)
* -trailing-garbage ( XC-ADDR U1 -- XC-ADDR U2 ) xchar-ext: Xchars and Unicode.
                                                            (line 11251)
* -[do ( COMPILATION -- DO-SYS ; RUN-TIME N1 N2 -- | LOOP-SYS ) gforth-experimental: Counted Loops.
                                                            (line  5998)
* -\d ( ADDR -- ADDR' ) regexp-pattern:  Regular Expressions.
                                                            (line 13857)
* -\s ( ADDR -- ADDR' ) regexp-pattern:  Regular Expressions.
                                                            (line 13860)
* -` ( "CHAR" -- ) regexp-pattern:       Regular Expressions.
                                                            (line 13868)
* . ( N -- ) core:                       Simple numeric output.
                                                            (line 10416)
* ." ( COMPILATION 'CCC"' -- ; RUN-TIME -- ) core: Miscellaneous output.
                                                            (line 10733)
* .( ( COMPILATION&INTERPRETATION "CCC<PAREN>" -- ) core-ext: Miscellaneous output.
                                                            (line 10739)
* ... ( X1 .. XN -- X1 .. XN ) gforth-1.0: Examining data.  (line 14231)
* ..char ( START END -- ) regexp-cg:     Regular Expressions.
                                                            (line 13826)
* .? ( ADDR -- ADDR' ) regexp-pattern:   Regular Expressions.
                                                            (line 13854)
* .cover-raw ( -- ) gforth-experimental: Code Coverage.     (line 14589)
* .coverage ( -- ) gforth-experimental:  Code Coverage.     (line 14576)
* .debugline ( NFILE NLINE -- ) gforth-0.6: Debugging.      (line 14352)
* .fpath ( -- ) gforth-0.4:              Source Search Paths.
                                                            (line 10130)
* .hm ( NT -- ) gforth-1.0:              Header methods.    (line 16215)
* .id ( NT -- ) gforth-0.6:              Name token.        (line  8253)
* .included ( -- ) gforth-0.5:           Forth source files.
                                                            (line  9873)
* .locale-csv ( -- ) gforth-experimental: i18n and l10n.    (line 11334)
* .path ( PATH-ADDR -- ) gforth-0.4:     General Search Paths.
                                                            (line 10170)
* .r ( N1 N2 -- ) core-ext:              Simple numeric output.
                                                            (line 10428)
* .recognizers ( -- ) gforth-experimental: Default Recognizers.
                                                            (line  9062)
* .s ( -- ) tools:                       Examining data.    (line 14234)
* .substitute ( ADDR1 LEN1 -- N / IOR ) gforth-experimental: Substitute.
                                                            (line 11359)
* .unresolved ( -- ) gforth-1.0:         Forward.           (line  7899)
* .voc ( WID -- ) gforth-0.2:            Word Lists.        (line  9419)
* .widget ( -- ) minos2:                 widget methods.    (line 19184)
* .\" ( COMPILATION 'CCC"' -- ; RUN-TIME -- ) gforth-0.6: Miscellaneous output.
                                                            (line 10730)
* / ( N1 N2 -- N ) core:                 Integer division.  (line  3909)
* // ( -- ) regexp-pattern:              Regular Expressions.
                                                            (line 13915)
* //g ( PTR ADDR U -- ADDR' U' ) regexp-replace: Regular Expressions.
                                                            (line 13965)
* //o ( PTR ADDR U -- ADDR' U' ) regexp-replace: Regular Expressions.
                                                            (line 13962)
* //s ( PTR -- ) regexp-replace:         Regular Expressions.
                                                            (line 13959)
* /COUNTED-STRING ( -- N ) environment:  Environmental Queries.
                                                            (line  9618)
* /f ( N1 N2 -- N ) gforth-1.0:          Integer division.  (line  3914)
* /f-stage1m ( N ADDR-RECI -- ) gforth-1.0: Two-stage integer division.
                                                            (line  4059)
* /f-stage2m ( N1 A-RECI -- NQUOTIENT ) gforth-1.0: Two-stage integer division.
                                                            (line  4063)
* /HOLD ( -- N ) environment:            Environmental Queries.
                                                            (line  9621)
* /l ( -- U ) gforth-0.7:                Address arithmetic.
                                                            (line  5181)
* /mod ( N1 N2 -- N3 N4 ) core:          Integer division.  (line  3927)
* /modf ( N1 N2 -- N3 N4 ) gforth-1.0:   Integer division.  (line  3933)
* /modf-stage2m ( N1 A-RECI -- UMODULUS NQUOTIENT ) gforth-1.0: Two-stage integer division.
                                                            (line  4071)
* /mods ( N1 N2 -- N3 N4 ) gforth-1.0:   Integer division.  (line  3930)
* /PAD ( -- N ) environment:             Environmental Queries.
                                                            (line  9624)
* /s ( N1 N2 -- N ) gforth-1.0:          Integer division.  (line  3912)
* /string ( C-ADDR1 U1 N -- C-ADDR2 U2 ) string: String words.
                                                            (line  5438)
* /w ( -- U ) gforth-0.7:                Address arithmetic.
                                                            (line  5178)
* /x ( -- U ) gforth-1.0:                Address arithmetic.
                                                            (line  5184)
* 0< ( N -- F ) core:                    Numeric comparison.
                                                            (line  4244)
* 0<= ( N -- F ) gforth-0.2:             Numeric comparison.
                                                            (line  4246)
* 0<> ( N -- F ) core-ext:               Numeric comparison.
                                                            (line  4248)
* 0= ( N -- F ) core:                    Numeric comparison.
                                                            (line  4250)
* 0> ( N -- F ) core-ext:                Numeric comparison.
                                                            (line  4252)
* 0>= ( N -- F ) gforth-0.2:             Numeric comparison.
                                                            (line  4254)
* 1+ ( N1 -- N2 ) core:                  Single precision.  (line  3802)
* 1- ( N1 -- N2 ) core:                  Single precision.  (line  3809)
* 1/f ( R1 -- R2 ) gforth-0.2:           Floating Point.    (line  4392)
* 2! ( W1 W2 A-ADDR -- ) core:           Memory Access.     (line  4893)
* 2* ( N1 -- N2 ) core:                  Bitwise operations.
                                                            (line  4164)
* 2, ( W1 W2 -- ) gforth-0.2:            Dictionary allocation.
                                                            (line  4741)
* 2/ ( N1 -- N2 ) core:                  Bitwise operations.
                                                            (line  4167)
* 2>r ( W1 W2 -- R:W1 R:W2 ) core-ext:   Return stack.      (line  4607)
* 2@ ( A-ADDR -- W1 W2 ) core:           Memory Access.     (line  4889)
* 2Constant ( W1 W2 "NAME" -- ) double:  Constants.         (line  6820)
* 2drop ( W1 W2 -- ) core:               Data stack.        (line  4549)
* 2dup ( W1 W2 -- W1 W2 W1 W2 ) core:    Data stack.        (line  4553)
* 2field: ( U1 "NAME" -- U2 ) gforth-0.7: Forth200x Structures.
                                                            (line 12501)
* 2Literal ( COMPILATION W1 W2 -- ; RUN-TIME -- W1 W2 ) double: Literals.
                                                            (line  8395)
* 2nip ( W1 W2 W3 W4 -- W3 W4 ) gforth-0.2: Data stack.     (line  4551)
* 2over ( W1 W2 W3 W4 -- W1 W2 W3 W4 W1 W2 ) core: Data stack.
                                                            (line  4555)
* 2r> ( R:W1 R:W2 -- W1 W2 ) core-ext:   Return stack.      (line  4609)
* 2r@ ( R:W1 R:W2 -- R:W1 R:W2 W1 W2 ) core-ext: Return stack.
                                                            (line  4611)
* 2rdrop ( R:W1 R:W2 -- ) gforth-0.2:    Return stack.      (line  4613)
* 2rot ( W1 W2 W3 W4 W5 W6 -- W3 W4 W5 W6 W1 W2 ) double-ext: Data stack.
                                                            (line  4561)
* 2swap ( W1 W2 W3 W4 -- W3 W4 W1 W2 ) core: Data stack.    (line  4559)
* 2tuck ( W1 W2 W3 W4 -- W3 W4 W1 W2 W3 W4 ) gforth-0.2: Data stack.
                                                            (line  4557)
* 2Value ( D "NAME" -- ) double-ext:     Values.            (line  6887)
* 2Variable ( "NAME" -- ) double:        Variables.         (line  6779)
* 2varue ( X1 X2 "NAME" -- ) gforth-1.0: Varues.            (line  6911)
* : ( "NAME" -- COLON-SYS ) core:        Colon Definitions. (line  6937)
* :: ( CLASS "NAME" -- ) mini-oof:       Basic Mini-OOF Usage.
                                                            (line 13518)
* :m ( "NAME" -- XT; RUN-TIME: OBJECT -- ) objects: Objects Glossary.
                                                            (line 13196)
* :noname ( -- XT COLON-SYS ) core-ext:  Anonymous Definitions.
                                                            (line  7007)
* :} ( HMADDR U LATEST LATESTNT WID 0 XT1 ... XTN -- ) gforth-1.0: Locals definition words.
                                                            (line 11608)
* :}d ( HMADDR U LATEST LATESTNT WID 0 A-ADDR1 U1 ... -- ) gforth-1.0: Closures.
                                                            (line 12072)
* :}h ( HMADDR U LATEST LATESTNT WID 0 A-ADDR1 U1 ... -- ) gforth-1.0: Closures.
                                                            (line 12076)
* :}h1 ( HMADDR U LATEST LATESTNT WID 0 A-ADDR1 U1 ... -- ) gforth-1.0: Closures.
                                                            (line 12080)
* :}l ( HMADDR U LATEST LATESTNT WID 0 A-ADDR1 U1 ... -- ) gforth-1.0: Closures.
                                                            (line 12068)
* :}xt ( HMADDR U LATEST LATESTNT WID 0 A-ADDR1 U1 ... -- ) gforth-1.0: Closures.
                                                            (line 12084)
* ; ( COMPILATION COLON-SYS -- ; RUN-TIME NEST-SYS -- ) core: Colon Definitions.
                                                            (line  6939)
* ;> ( -- ) gforth-experimental:         Closures.          (line 12136)
* ;abi-code ( -- ) gforth-1.0:           Assembler Definitions.
                                                            (line 15410)
* ;code ( COMPILATION. COLON-SYS1 -- COLON-SYS2 ) tools-ext: Assembler Definitions.
                                                            (line 15433)
* ;inline ( INLINE:-SYS -- ) gforth-experimental: Colon Definitions.
                                                            (line  6952)
* ;m ( COLON-SYS --; RUN-TIME: -- ) objects: Objects Glossary.
                                                            (line 13200)
* ;s ( R:W -- ) gforth-0.2:              Calls and returns. (line  6415)
* ;] ( COMPILE-TIME: QUOTATION-SYS -- ; RUN-TIME: -- XT ) gforth-1.0: Quotations.
                                                            (line  7074)
* < ( N1 N2 -- F ) core:                 Numeric comparison.
                                                            (line  4232)
* <# ( -- ) core:                        Formatted numeric output.
                                                            (line 10497)
* << ( RUN-ADDR ADDR U -- RUN-ADDR ) regexp-replace: Regular Expressions.
                                                            (line 13950)
* <<" ( "STRING<">" -- ) regexp-replace: Regular Expressions.
                                                            (line 13953)
* <<# ( -- ) gforth-0.5:                 Formatted numeric output.
                                                            (line 10500)
* <= ( N1 N2 -- F ) gforth-0.2:          Numeric comparison.
                                                            (line  4234)
* <> ( N1 N2 -- F ) core-ext:            Numeric comparison.
                                                            (line  4236)
* <bind> ( CLASS SELECTOR-XT -- XT ) objects: Objects Glossary.
                                                            (line 13102)
* <to-inst> ( W XT -- ) objects:         Objects Glossary.  (line 13241)
* <{: ( -- HMADDR U LATEST LATESTNT WID 0 ) gforth-experimental: Closures.
                                                            (line 12133)
* = ( N1 N2 -- F ) core:                 Numeric comparison.
                                                            (line  4238)
* =mkdir ( C-ADDR U WMODE -- WIOR ) gforth-0.7: Directories.
                                                            (line 10080)
* > ( N1 N2 -- F ) core:                 Numeric comparison.
                                                            (line  4240)
* >= ( N1 N2 -- F ) gforth-0.2:          Numeric comparison.
                                                            (line  4242)
* >> ( ADDR -- ADDR ) regexp-replace:    Regular Expressions.
                                                            (line 13946)
* >addr ( XT -- ADDR ) gforth-experimental: Closures.       (line 12089)
* >animate ( RDELTA ADDR XT -- ) minos2: widget methods.    (line 19202)
* >body ( XT -- A_ADDR ) core:           CREATE..DOES> details.
                                                            (line  7401)
* >code-address ( XT -- C_ADDR ) gforth-0.2: Threading Words.
                                                            (line 16448)
* >compile ( TRANSLATOR -- ) gforth-experimental: Dealing with existing Recognizers.
                                                            (line  9209)
* >definer ( XT -- DEFINER ) gforth-0.2: Threading Words.   (line 16509)
* >does-code ( XT1 -- XT2 ) gforth-0.2:  Threading Words.   (line 16491)
* >float ( C-ADDR U -- F:... FLAG ) floating: Line input and conversion.
                                                            (line 11099)
* >float1 ( C-ADDR U C -- F:... FLAG ) gforth-1.0: Line input and conversion.
                                                            (line 11107)
* >in ( -- ADDR ) core:                  The Text Interpreter.
                                                            (line  8751)
* >interpret ( TRANSLATOR -- ) gforth-experimental: Dealing with existing Recognizers.
                                                            (line  9206)
* >l ( W -- ) gforth-0.2:                Locals implementation.
                                                            (line 11942)
* >name ( XT -- NT|0 ) gforth-0.2:       Name token.        (line  8220)
* >number ( UD1 C-ADDR1 U1 -- UD2 C-ADDR2 U2 ) core: Line input and conversion.
                                                            (line 11086)
* >o ( C-ADDR -- R:C-OLD ) new:          Mini-OOF2.         (line 13693)
* >order ( WID -- ) gforth-0.5:          Word Lists.        (line  9394)
* >postpone ( TRANSLATOR -- ) gforth-experimental: Dealing with existing Recognizers.
                                                            (line  9212)
* >pow2 ( U1 -- U2 ) gforth-1.0:         Bitwise operations.
                                                            (line  4178)
* >r ( W -- R:W ) core:                  Return stack.      (line  4599)
* >string-execute ( ... XT -- ... ADDR U ) gforth-1.0: String words.
                                                            (line  5481)
* >time&date&tz ( UDTIME -- NSEC NMIN NHOUR NDAY NMONTH NYEAR FDST NDSTOFF C-ADDRTZ UTZ ) gforth-1.0: Keeping track of Time.
                                                            (line 16566)
* ? ( A-ADDR -- ) tools:                 Examining data.    (line 14277)
* ?!@ ( UNEW UOLD A-ADDR -- UPREV ) gforth-experimental: Hardware operations for multi-tasking.
                                                            (line 14821)
* ??? ( -- ) gforth-0.2:                 Debugging.         (line 14374)
* ?cov+ ( FLAG -- FLAG ) gforth-experimental: Code Coverage.
                                                            (line 14569)
* ?DO ( COMPILATION -- DO-SYS ; RUN-TIME W1 W2 -- | LOOP-SYS ) core-ext: Counted Loops.
                                                            (line  5984)
* ?dup ( W -- S:... W ) core:            Data stack.        (line  4543)
* ?DUP-0=-IF ( COMPILATION -- ORIG ; RUN-TIME N -- N| ) gforth-0.2: Arbitrary control structures.
                                                            (line  6293)
* ?dup-IF ( COMPILATION -- ORIG ; RUN-TIME N -- N| ) gforth-0.2: Arbitrary control structures.
                                                            (line  6288)
* ?events ( -- ) gforth-experimental:    Message queues.    (line 14852)
* ?EXIT ( -- ) gforth-0.2:               Calls and returns. (line  6412)
* ?inside ( RX RY -- ACT / 0 ) minos2:   actor methods.     (line 19055)
* ?LEAVE ( COMPILATION -- ; RUN-TIME F | F LOOP-SYS -- ) gforth-0.2: Counted Loops.
                                                            (line  6061)
* ?of ( COMPILATION -- OF-SYS ; RUN-TIME F -- ) gforth-1.0: Arbitrary control structures.
                                                            (line  6314)
* @ ( A-ADDR -- W ) core:                Memory Access.     (line  4874)
* @localn ( NOFFSET -- W ) gforth-1.0:   Locals implementation.
                                                            (line 11932)
* [ ( -- ) core:                         Literals.          (line  8374)
* ['] ( COMPILATION. "NAME" -- ; RUN-TIME. -- XT ) core: Execution token.
                                                            (line  8110)
* [+LOOP] ( N -- ) gforth-0.2:           Interpreter Directives.
                                                            (line  8967)
* [: ( COMPILE-TIME: -- QUOTATION-SYS FLAG COLON-SYS ) gforth-1.0: Quotations.
                                                            (line  7071)
* [?DO] ( N-LIMIT N-INDEX -- ) gforth-0.2: Interpreter Directives.
                                                            (line  8961)
* [AGAIN] ( -- ) gforth-0.2:             Interpreter Directives.
                                                            (line  8987)
* [BEGIN] ( -- ) gforth-0.2:             Interpreter Directives.
                                                            (line  8983)
* [bind] ( COMPILE-TIME: "CLASS" "SELECTOR" -- ; RUN-TIME: ... OBJECT -- ... ) objects: Objects Glossary.
                                                            (line 13108)
* [char] ( COMPILATION '<SPACES>CCC' -- ; RUN-TIME -- C ) core,xchar-ext: String and character literals.
                                                            (line  5347)
* [COMP'] ( COMPILATION "NAME" -- ; RUN-TIME -- W XT ) gforth-0.2: Compilation token.
                                                            (line  8308)
* [compile] ( COMPILATION "NAME" -- ; RUN-TIME ? -- ? ) core-ext: Macros.
                                                            (line  8620)
* [current] ( COMPILE-TIME: "SELECTOR" -- ; RUN-TIME: ... OBJECT -- ... ) objects: Objects Glossary.
                                                            (line 13141)
* [defined] ( "<SPACES>NAME" -- FLAG ) tools-ext: Interpreter Directives.
                                                            (line  8945)
* [DO] ( N-LIMIT N-INDEX -- ) gforth-0.2: Interpreter Directives.
                                                            (line  8963)
* [ELSE] ( -- ) tools-ext:               Interpreter Directives.
                                                            (line  8929)
* [ENDIF] ( -- ) gforth-0.2:             Interpreter Directives.
                                                            (line  8942)
* [FOR] ( N -- ) gforth-0.2:             Interpreter Directives.
                                                            (line  8969)
* [IFDEF] ( "<SPACES>NAME" -- ) gforth-0.2: Interpreter Directives.
                                                            (line  8951)
* [IFUNDEF] ( "<SPACES>NAME" -- ) gforth-0.2: Interpreter Directives.
                                                            (line  8956)
* [IF] ( FLAG -- ) tools-ext:            Interpreter Directives.
                                                            (line  8921)
* [I] ( RUN-TIME -- N ) gforth-0.2:      Interpreter Directives.
                                                            (line  8973)
* [LOOP] ( -- ) gforth-0.2:              Interpreter Directives.
                                                            (line  8965)
* [NEXT] ( N -- ) gforth-0.2:            Interpreter Directives.
                                                            (line  8971)
* [parent] ( COMPILE-TIME: "SELECTOR" -- ; RUN-TIME: ... OBJECT -- ... ) objects: Objects Glossary.
                                                            (line 13219)
* [REPEAT] ( -- ) gforth-0.2:            Interpreter Directives.
                                                            (line  8991)
* [THEN] ( -- ) tools-ext:               Interpreter Directives.
                                                            (line  8938)
* [to-inst] ( COMPILE-TIME: "NAME" -- ; RUN-TIME: W -- ) objects: Objects Glossary.
                                                            (line 13244)
* [undefined] ( "<SPACES>NAME" -- FLAG ) tools-ext: Interpreter Directives.
                                                            (line  8948)
* [UNTIL] ( FLAG -- ) gforth-0.2:        Interpreter Directives.
                                                            (line  8985)
* [WHILE] ( FLAG -- ) gforth-0.2:        Interpreter Directives.
                                                            (line  8989)
* [{: ( -- HMADDR U LATEST LATESTNT WID 0 ) gforth-experimental: Closures.
                                                            (line 12057)
* \ ( COMPILATION 'CCC<NEWLINE>' -- ; RUN-TIME -- ) core-ext,block-ext: Comments.
                                                            (line  3744)
* \$ ( ADDR -- ADDR ) regexp-pattern:    Regular Expressions.
                                                            (line 13877)
* \( ( ADDR -- ADDR ) regexp-pattern:    Regular Expressions.
                                                            (line 13932)
* \) ( ADDR -- ADDR ) regexp-pattern:    Regular Expressions.
                                                            (line 13935)
* \0 ( -- ADDR U ) regexp-pattern:       Regular Expressions.
                                                            (line 13938)
* \c ( "REST-OF-LINE" -- ) gforth-0.7:   Declaring C Functions.
                                                            (line 15062)
* \d ( ADDR -- ADDR' ) regexp-pattern:   Regular Expressions.
                                                            (line 13848)
* \G ( COMPILATION 'CCC<NEWLINE>' -- ; RUN-TIME -- ) gforth-0.2: Comments.
                                                            (line  3750)
* \s ( ADDR -- ADDR' ) regexp-pattern:   Regular Expressions.
                                                            (line 13851)
* \\\ ( -- ) gforth-1.0:                 Forth source files.
                                                            (line  9870)
* \^ ( ADDR -- ADDR ) regexp-pattern:    Regular Expressions.
                                                            (line 13874)
* ] ( -- ) core:                         Literals.          (line  8377)
* ]L ( COMPILATION: N -- ; RUN-TIME: -- N ) gforth-0.5: Literals.
                                                            (line  8389)
* ]nocov ( -- ) gforth-1.0:              Code Coverage.     (line 14560)
* ]] ( -- ) gforth-0.6:                  Macros.            (line  8464)
* ` ( "CHAR" -- ) regexp-pattern:        Regular Expressions.
                                                            (line 13863)
* `? ( "CHAR" -- ) regexp-pattern:       Regular Expressions.
                                                            (line 13866)
* { ( -- HMADDR U LATEST LATESTNT WID 0 ) gforth-0.2: Locals definition words.
                                                            (line 11611)
* {* ( ADDR -- ADDR ADDR ) regexp-pattern: Regular Expressions.
                                                            (line 13900)
* {** ( ADDR -- ADDR ADDR ) regexp-pattern: Regular Expressions.
                                                            (line 13888)
* {+ ( ADDR -- ADDR ADDR ) regexp-pattern: Regular Expressions.
                                                            (line 13906)
* {++ ( ADDR -- ADDR ADDR ) regexp-pattern: Regular Expressions.
                                                            (line 13894)
* {: ( -- HMADDR U LATEST LATESTNT WID 0 ) local-ext: Locals definition words.
                                                            (line 11596)
* {{ ( ADDR -- ADDR ADDR ) regexp-pattern: Regular Expressions.
                                                            (line 13920)
* | ( -- ) gforth-1.0:                   Locals definition words.
                                                            (line 11604)
* || ( ADDR ADDR -- ADDR ADDR ) regexp-pattern: Regular Expressions.
                                                            (line 13923)
* } ( HMADDR U LATEST LATESTNT WID 0 XT1 ... XTN -- ) gforth-0.2: Locals definition words.
                                                            (line 11615)
* }} ( ADDR ADDR -- ADDR ) regexp-pattern: Regular Expressions.
                                                            (line 13926)
* ~~ ( -- ) gforth-0.2:                  Debugging.         (line 14346)
* ~~1bt ( -- ) gforth-1.0:               Debugging.         (line 14371)
* ~~bt ( -- ) gforth-1.0:                Debugging.         (line 14368)
* ~~Value ( N "NAME" -- ) gforth-1.0:    Debugging.         (line 14389)
* ~~Variable ( "NAME" -- ) gforth-1.0:   Debugging.         (line 14386)
* A, ( ADDR -- ) gforth-0.2:             Dictionary allocation.
                                                            (line  4753)
* abi-code ( "NAME" -- COLON-SYS ) gforth-1.0: Assembler Definitions.
                                                            (line 15402)
* abort ( ?? -- ?? ) core,exception-ext: Exception Handling.
                                                            (line  6664)
* ABORT" ( COMPILATION 'CCC"' -- ; RUN-TIME F -- ) core,exception-ext: Exception Handling.
                                                            (line  6659)
* abs ( N -- U ) core:                   Single precision.  (line  3815)
* absolute-file? ( ADDR U -- FLAG ) gforth-1.0: Search Paths.
                                                            (line 10115)
* accept ( C-ADDR +N1 -- +N2 ) core:     Line input and conversion.
                                                            (line 11067)
* AConstant ( ADDR "NAME" -- ) gforth-0.2: Constants.       (line  6816)
* act ( -- OPTR ) minos2:                widget methods.    (line 19091)
* act-name$ ( -- ADDR U ) minos2:        actor methods.     (line 19034)
* action-of ( INTERPRETATION "NAME" -- XT; COMPILATION "NAME" -- ; RUN-TIME -- XT ) core-ext: Deferred Words.
                                                            (line  7868)
* activate ( RUN-TIME NEST-SYS1 TASK -- ) gforth-experimental: Basic multi-tasking.
                                                            (line 14676)
* active-w ( -- OPTR ) minos2:           actor methods.     (line 19031)
* actor ( -- CLASS ) minos2:             MINOS2 object framework.
                                                            (line 19019)
* add-cflags ( C-ADDR U -- ) gforth-1.0: Declaring OS-level libraries.
                                                            (line 15215)
* add-framework ( C-ADDR U -- ) gforth-1.0: Declaring OS-level libraries.
                                                            (line 15208)
* add-incdir ( C-ADDR U -- ) gforth-1.0: Declaring OS-level libraries.
                                                            (line 15212)
* add-ldflags ( C-ADDR U -- ) gforth-1.0: Declaring OS-level libraries.
                                                            (line 15218)
* add-lib ( C-ADDR U -- ) gforth-0.7:    Declaring OS-level libraries.
                                                            (line 15200)
* add-libpath ( C-ADDR U -- ) gforth-0.7: Declaring OS-level libraries.
                                                            (line 15204)
* addr ( "NAME" -- ADDR ) gforth-1.0:    Varues.            (line  6919)
* ADDRESS-UNIT-BITS ( -- N ) environment: Environmental Queries.
                                                            (line  9612)
* adjust-buffer ( U ADDR -- ) gforth-experimental: Heap Allocation.
                                                            (line  4856)
* after-locate ( -- U ) gforth-1.0:      Locating source code definitions.
                                                            (line 14027)
* AGAIN ( COMPILATION DEST -- ; RUN-TIME -- ) core-ext: Arbitrary control structures.
                                                            (line  6247)
* AHEAD ( COMPILATION -- ORIG ; RUN-TIME -- ) tools-ext: Arbitrary control structures.
                                                            (line  6231)
* Alias ( XT "NAME" -- ) gforth-0.2:     Aliases.           (line  7926)
* align ( -- ) core:                     Dictionary allocation.
                                                            (line  4772)
* aligned ( C-ADDR -- A-ADDR ) core:     Address arithmetic.
                                                            (line  5096)
* ALiteral ( COMPILATION ADDR -- ; RUN-TIME -- ADDR ) gforth-0.2: Literals.
                                                            (line  8385)
* allocate ( U -- A_ADDR WIOR ) memory:  Heap Allocation.   (line  4808)
* allot ( N -- ) core:                   Dictionary allocation.
                                                            (line  4721)
* also ( -- ) search-ext:                Word Lists.        (line  9400)
* also-path ( C-ADDR LEN PATH-ADDR -- ) gforth-0.4: General Search Paths.
                                                            (line 10167)
* and ( W1 W2 -- W ) core:               Bitwise operations.
                                                            (line  4129)
* annotate-cov ( -- ) gforth-experimental: Code Coverage.   (line 14579)
* append ( C-ADDR1 U1 C-ADDR2 U2 -- C-ADDR U ) gforth-0.7: String words.
                                                            (line  5476)
* arg ( U -- ADDR COUNT ) gforth-0.2:    OS command line arguments.
                                                            (line 11431)
* argc ( -- ADDR ) gforth-0.2:           OS command line arguments.
                                                            (line 11445)
* argv ( -- ADDR ) gforth-0.2:           OS command line arguments.
                                                            (line 11449)
* arshift ( N1 U -- N2 ) gforth-1.0:     Bitwise operations.
                                                            (line  4149)
* asptr ( CLASS -- ) oof:                Class Declaration. (line 13449)
* assembler ( -- ) tools-ext:            Assembler Definitions.
                                                            (line 15395)
* assert( ( -- ) gforth-0.2:             Assertions.        (line 14441)
* assert-level ( -- A-ADDR ) gforth-0.2: Assertions.        (line 14460)
* assert0( ( -- ) gforth-0.2:            Assertions.        (line 14428)
* assert1( ( -- ) gforth-0.2:            Assertions.        (line 14431)
* assert2( ( -- ) gforth-0.2:            Assertions.        (line 14434)
* assert3( ( -- ) gforth-0.2:            Assertions.        (line 14437)
* ASSUME-LIVE ( ORIG -- ORIG ) gforth-0.2: Where are locals visible by name?.
                                                            (line 11804)
* at-deltaxy ( DX DY -- ) gforth-0.7:    Terminal output.   (line 10806)
* at-xy ( X Y -- ) facility:             Terminal output.   (line 10802)
* AUser ( "NAME" -- ) gforth-0.2:        Task-local data.   (line 14743)
* authors ( -- ) gforth-1.0:             Help on Gforth.    (line   716)
* AValue ( W "NAME" -- ) gforth-0.6:     Values.            (line  6883)
* AVariable ( "NAME" -- ) gforth-0.2:    Variables.         (line  6775)
* b ( -- ) gforth-1.0:                   Locating source code definitions.
                                                            (line 14013)
* barrier ( -- ) gforth-experimental:    Hardware operations for multi-tasking.
                                                            (line 14830)
* base ( -- A-ADDR ) core:               Number Conversion. (line  8855)
* base-execute ( I*X XT U -- J*X ) gforth-0.7: Number Conversion.
                                                            (line  8851)
* baseline ( -- R ) minos2:              widget methods.    (line 19115)
* basename ( C-ADDR1 U1 -- C-ADDR2 U2 ) gforth-0.7: Directories.
                                                            (line 10037)
* before-line ( -- ) gforth-1.0:         Text Interpreter Hooks.
                                                            (line  9230)
* before-locate ( -- U ) gforth-1.0:     Locating source code definitions.
                                                            (line 14024)
* before-word ( -- ) gforth-0.7:         Text Interpreter Hooks.
                                                            (line  9233)
* BEGIN ( COMPILATION -- DEST ; RUN-TIME -- ) core: Arbitrary control structures.
                                                            (line  6239)
* begin-structure ( "NAME" -- STRUCT-SYS 0 ) facility-ext: Forth200x Structures.
                                                            (line 12482)
* bin ( FAM1 -- FAM2 ) file:             General files.     (line  9903)
* bind ( ... "CLASS" "SELECTOR" -- ... ) objects: Objects Glossary.
                                                            (line 13099)
* bind' ( "CLASS" "SELECTOR" -- XT ) objects: Objects Glossary.
                                                            (line 13105)
* bl ( -- C-CHAR ) core:                 String and character literals.
                                                            (line  5374)
* blank ( C-ADDR U -- ) string:          Memory Blocks.     (line  5224)
* blk ( -- ADDR ) block:                 Input Sources.     (line  8806)
* block ( U -- A-ADDR ) block:           Blocks.            (line 10331)
* block-included ( A-ADDR U -- ) gforth-0.2: Blocks.        (line 10390)
* block-offset ( -- ADDR ) gforth-0.5:   Blocks.            (line 10310)
* block-position ( U -- ) block:         Blocks.            (line 10320)
* bootmessage ( -- ) gforth-0.4:         Modifying the Startup Sequence.
                                                            (line 18349)
* border ( -- R ) minos2:                widget methods.    (line 19124)
* borderl ( -- R ) minos2:               widget methods.    (line 19133)
* bordert ( -- R ) minos2:               widget methods.    (line 19130)
* borderv ( -- R ) minos2:               widget methods.    (line 19127)
* bounds ( U1 U2 -- U3 U1 ) gforth-0.2:  Counted Loops.     (line  5993)
* break" ( 'CCC"' -- ) gforth-0.4:       Singlestep Debugger.
                                                            (line 14541)
* break: ( -- ) gforth-0.4:              Singlestep Debugger.
                                                            (line 14539)
* broken-pipe-error ( -- N ) gforth-0.6: Pipes.             (line 11150)
* browse ( "SUBNAME" -- ) gforth-1.0:    Locating source code definitions.
                                                            (line 14038)
* bt ( -- ) gforth-1.0:                  Locating exception source.
                                                            (line 14105)
* buffer ( U -- A-ADDR ) block:          Blocks.            (line 10338)
* buffer% ( U1 U2 -- ) gforth-experimental: Heap Allocation.
                                                            (line  4851)
* buffer: ( U "NAME" -- ) core-ext:      Variables.         (line  6785)
* bw ( -- ) gforth-1.0:                  Locating uses of a word.
                                                            (line 14061)
* bw-cover ( -- ) gforth-1.0:            Code Coverage.     (line 14596)
* c! ( C C-ADDR -- ) core:               Memory Access.     (line  4886)
* C" ( COMPILATION "CCC<QUOTE>" -- ; RUN-TIME -- C-ADDR ) core-ext: Counted string words.
                                                            (line  5673)
* c$+! ( CHAR $ADDR -- ) gforth-1.0:     $tring words.      (line  5544)
* c, ( C -- ) core:                      Dictionary allocation.
                                                            (line  4731)
* c-callback ( "FORTH-NAME" "{TYPE}" "---" "TYPE" -- ) gforth-1.0: Callbacks.
                                                            (line 15234)
* c-callback-thread ( "FORTH-NAME" "{TYPE}" "---" "TYPE" -- ) gforth-1.0: Callbacks.
                                                            (line 15239)
* c-function ( "FORTH-NAME" "C-NAME" "{TYPE}" "---" "TYPE" -- ) gforth-0.7: Declaring C Functions.
                                                            (line 15065)
* c-funptr ( "FORTH-NAME" <{>"C-TYPECAST"<}> "{TYPE}" "---" "TYPE" -- ) gforth-1.0: Calling C function pointers.
                                                            (line 15092)
* c-library ( "NAME" -- ) gforth-0.7:    Defining library interfaces.
                                                            (line 15164)
* c-library-name ( C-ADDR U -- ) gforth-0.7: Defining library interfaces.
                                                            (line 15161)
* c-value ( "FORTH-NAME" "C-NAME" "---" "TYPE" -- ) gforth-1.0: Declaring C Functions.
                                                            (line 15069)
* c-variable ( "FORTH-NAME" "C-NAME" -- ) gforth-1.0: Declaring C Functions.
                                                            (line 15073)
* C: ( COMPILATION "NAME" -- A-ADDR XT; RUN-TIME C -- ) gforth-0.2: Locals definition words.
                                                            (line 11637)
* c>s ( X -- N ) gforth-1.0:             Special Memory Accesses.
                                                            (line  5015)
* c? ( ADDR CLASS -- ) regexp-pattern:   Regular Expressions.
                                                            (line 13842)
* c@ ( C-ADDR -- C ) core:               Memory Access.     (line  4883)
* CA: ( COMPILATION "NAME" -- A-ADDR XT; RUN-TIME C -- ) gforth-1.0: Locals definition words.
                                                            (line 11640)
* call-c ( ... W -- ... ) gforth-0.2:    Low-Level C Interface Words.
                                                            (line 15289)
* caller-w ( -- OPTR ) minos2:           actor methods.     (line 19028)
* capscompare ( C-ADDR1 U1 C-ADDR2 U2 -- N ) gforth-0.7: String words.
                                                            (line  5455)
* capssearch ( C-ADDR1 U1 C-ADDR2 U2 -- C-ADDR3 U3 FLAG ) gforth-1.0: String words.
                                                            (line  5466)
* capsstring-prefix? ( C-ADDR1 U1 C-ADDR2 U2 -- F ) gforth-1.0: String words.
                                                            (line  5462)
* case ( COMPILATION -- CASE-SYS ; RUN-TIME -- ) core-ext: Arbitrary control structures.
                                                            (line  6297)
* catch ( X1 .. XN XT -- Y1 .. YM 0 / Z1 .. ZN ERROR ) exception: Exception Handling.
                                                            (line  6498)
* cell ( -- U ) gforth-0.2:              Address arithmetic.
                                                            (line  5093)
* cell% ( -- ALIGN SIZE ) gforth-0.4:    Structure Glossary.
                                                            (line 12415)
* cell+ ( A-ADDR1 -- A-ADDR2 ) core:     Address arithmetic.
                                                            (line  5084)
* cell- ( A-ADDR1 -- A-ADDR2 ) core:     Address arithmetic.
                                                            (line  5087)
* cell/ ( N1 -- N2 ) gforth-1.0:         Address arithmetic.
                                                            (line  5090)
* cells ( N1 -- N2 ) core:               Address arithmetic.
                                                            (line  5081)
* cfalign ( -- ) gforth-0.2:             Dictionary allocation.
                                                            (line  4791)
* cfaligned ( ADDR1 -- ADDR2 ) gforth-0.2: Address arithmetic.
                                                            (line  5145)
* cfield: ( U1 "NAME" -- U2 ) facility-ext: Forth200x Structures.
                                                            (line 12495)
* char ( '<SPACES>CCC' -- C ) core,xchar-ext: String and character literals.
                                                            (line  5343)
* char% ( -- ALIGN SIZE ) gforth-0.4:    Structure Glossary.
                                                            (line 12417)
* char+ ( C-ADDR1 -- C-ADDR2 ) core:     Address arithmetic.
                                                            (line  5076)
* char- ( C-ADDR1 -- C-ADDR2 ) gforth-0.7: Address arithmetic.
                                                            (line  5079)
* charclass ( -- ) regexp-cg:            Regular Expressions.
                                                            (line 13817)
* chars ( N1 -- N2 ) core:               Address arithmetic.
                                                            (line  5073)
* cilk-bye ( -- ) cilk:                  Cilk.              (line 14910)
* cilk-init ( -- ) cilk:                 Cilk.              (line 14892)
* cilk-sync ( -- ) cilk:                 Cilk.              (line 14907)
* class ( CLASS -- CLASS SELECTORS VARS ) mini-oof: Basic Mini-OOF Usage.
                                                            (line 13506)
* class ( PARENT-CLASS -- ALIGN OFFSET ) objects: Objects Glossary.
                                                            (line 13111)
* class->map ( CLASS -- MAP ) objects:   Objects Glossary.  (line 13115)
* class-inst-size ( CLASS -- ADDR ) objects: Objects Glossary.
                                                            (line 13120)
* class-override! ( XT SEL-XT CLASS-MAP -- ) objects: Objects Glossary.
                                                            (line 13124)
* class-previous ( CLASS -- ) objects:   Objects Glossary.  (line 13127)
* class; ( -- ) oof:                     Class Declaration. (line 13475)
* class>order ( CLASS -- ) objects:      Objects Glossary.  (line 13131)
* clear-libs ( -- ) gforth-0.7:          Declaring OS-level libraries.
                                                            (line 15197)
* clear-path ( PATH-ADDR -- ) gforth-0.5: General Search Paths.
                                                            (line 10164)
* clearstack ( ... -- ) gforth-0.2:      Examining data.    (line 14266)
* clearstacks ( ... -- ) gforth-0.7:     Examining data.    (line 14272)
* clicked ( RX RY BMASK N -- ) minos2:   actor methods.     (line 19037)
* close-dir ( WDIRID -- WIOR ) gforth-0.5: Directories.     (line 10064)
* close-file ( WFILEID -- WIOR ) file:   General files.     (line  9917)
* close-pipe ( WFILEID -- WRETVAL WIOR ) gforth-0.2: Pipes. (line 11141)
* cmove ( C-FROM C-TO U -- ) string:     Memory Blocks.     (line  5208)
* cmove> ( C-FROM C-TO U -- ) string:    Memory Blocks.     (line  5213)
* code ( "NAME" -- COLON-SYS ) tools-ext: Assembler Definitions.
                                                            (line 15426)
* code-address! ( C_ADDR XT -- ) gforth-obsolete: Threading Words.
                                                            (line 16451)
* color-cover ( -- ) gforth-1.0:         Code Coverage.     (line 14599)
* color: ( RGBA "NAME" -- ) minos2:      widget methods.    (line 19210)
* common-list ( LIST1 LIST2 -- LIST3 ) gforth-internal: Locals implementation.
                                                            (line 12012)
* COMP' ( "NAME" -- W XT ) gforth-0.2:   Compilation token. (line  8311)
* compare ( C-ADDR1 U1 C-ADDR2 U2 -- N ) string: Memory Blocks.
                                                            (line  5235)
* compile, ( XT -- ) core-ext:           Macros.            (line  8575)
* compile-lp+! ( N -- ) gforth-0.2:      Locals implementation.
                                                            (line 11952)
* compile-only ( -- ) gforth-0.2:        Interpretation and Compilation Semantics.
                                                            (line  7991)
* compile-only? ( NT -- FLAG ) gforth-1.0: Header fields.   (line 16169)
* const-does> ( RUN-TIME: W*UW R*UR UW UR "NAME" -- ) gforth-obsolete: Const-does>.
                                                            (line  7749)
* Constant ( W "NAME" -- ) core:         Constants.         (line  6811)
* construct ( ... OBJECT -- ) objects:   Objects Glossary.  (line 13134)
* context ( -- ADDR ) gforth-0.2:        Word Lists.        (line  9484)
* contof ( COMPILATION CASE-SYS1 OF-SYS -- CASE-SYS2 ; RUN-TIME -- ) gforth-1.0: Arbitrary control structures.
                                                            (line  6321)
* convert ( UD1 C-ADDR1 -- UD2 C-ADDR2 ) core-ext-obsolescent: Line input and conversion.
                                                            (line 11117)
* CORE ( -- F ) environment:             Environmental Queries.
                                                            (line  9627)
* CORE-EXT ( -- F ) environment:         Environmental Queries.
                                                            (line  9631)
* cores ( -- U ) cilk:                   Cilk.              (line 14886)
* count ( C-ADDR1 -- C-ADDR2 U ) core:   Counted string words.
                                                            (line  5665)
* Country ( <LANG> "NAME" -- ) gforth-experimental: i18n and l10n.
                                                            (line 11312)
* cov% ( -- ) gforth-experimental:       Code Coverage.     (line 14585)
* cov+ ( -- ) gforth-experimental:       Code Coverage.     (line 14566)
* coverage? ( -- F ) gforth-internal:    Code Coverage.     (line 14563)
* cputime ( -- DUSER DSYSTEM ) gforth-0.5: Keeping track of Time.
                                                            (line 16578)
* cr ( -- ) core:                        Miscellaneous output.
                                                            (line 10710)
* Create ( "NAME" -- ) core:             CREATE.            (line  6709)
* create-file ( C-ADDR U WFAM -- WFILEID WIOR ) file: General files.
                                                            (line  9915)
* create-from ( NT "NAME" -- ) gforth-1.0: Creating from a prototype.
                                                            (line  7701)
* critical-section ( XT SEMAPHORE -- ) gforth-experimental: Semaphores.
                                                            (line 14800)
* CS-DROP ( DEST -- ) gforth-1.0:        Arbitrary control structures.
                                                            (line  6255)
* CS-PICK ( ORIG0/DEST0 ORIG1/DEST1 ... ORIGU/DESTU U -- ... ORIG0/DEST0 ) tools-ext: Arbitrary control structures.
                                                            (line  6251)
* CS-ROLL ( DESTU/ORIGU .. DEST0/ORIG0 U -- .. DEST0/ORIG0 DESTU/ORIGU ) tools-ext: Arbitrary control structures.
                                                            (line  6253)
* cs-vocabulary ( "NAME" -- ) gforth-1.0: Word Lists.       (line  9391)
* cs-wordlist ( -- WID ) gforth-1.0:     Word Lists.        (line  9388)
* cstring>sstring ( C-ADDR -- C-ADDR U ) gforth-0.2: String words.
                                                            (line  5447)
* ctz ( X -- U ) gforth-1.0:             Bitwise operations.
                                                            (line  4189)
* current ( -- ADDR ) gforth-0.2:        Word Lists.        (line  9481)
* current' ( "SELECTOR" -- XT ) objects: Objects Glossary.  (line 13138)
* current-interface ( -- ADDR ) objects: Objects Glossary.  (line 13144)
* C^ ( COMPILATION "NAME" -- A-ADDR XT; RUN-TIME C -- ) gforth-0.2: Locals definition words.
                                                            (line 11643)
* d ( -- R ) minos2:                     widget methods.    (line 19109)
* d+ ( UD1 UD2 -- UD ) double:           Double precision.  (line  3847)
* d- ( D1 D2 -- D ) double:              Double precision.  (line  3849)
* d. ( D -- ) double:                    Simple numeric output.
                                                            (line 10441)
* d.r ( D N -- ) double:                 Simple numeric output.
                                                            (line 10449)
* d0< ( D -- F ) double:                 Numeric comparison.
                                                            (line  4285)
* d0<= ( D -- F ) gforth-0.2:            Numeric comparison.
                                                            (line  4287)
* d0<> ( D -- F ) gforth-0.2:            Numeric comparison.
                                                            (line  4289)
* d0= ( D -- F ) double:                 Numeric comparison.
                                                            (line  4291)
* d0> ( D -- F ) gforth-0.2:             Numeric comparison.
                                                            (line  4293)
* d0>= ( D -- F ) gforth-0.2:            Numeric comparison.
                                                            (line  4295)
* d2* ( D1 -- D2 ) double:               Bitwise operations.
                                                            (line  4171)
* d2/ ( D1 -- D2 ) double:               Bitwise operations.
                                                            (line  4174)
* D: ( COMPILATION "NAME" -- A-ADDR XT; RUN-TIME X1 X2 -- ) gforth-0.2: Locals definition words.
                                                            (line 11628)
* d< ( D1 D2 -- F ) double:              Numeric comparison.
                                                            (line  4273)
* d<= ( D1 D2 -- F ) gforth-0.2:         Numeric comparison.
                                                            (line  4275)
* d<> ( D1 D2 -- F ) gforth-0.2:         Numeric comparison.
                                                            (line  4277)
* d= ( D1 D2 -- F ) double:              Numeric comparison.
                                                            (line  4279)
* d> ( D1 D2 -- F ) gforth-0.2:          Numeric comparison.
                                                            (line  4281)
* d>= ( D1 D2 -- F ) gforth-0.2:         Numeric comparison.
                                                            (line  4283)
* d>f ( D -- R ) floating:               Floating Point.    (line  4328)
* d>s ( D -- N ) double:                 Double precision.  (line  3845)
* DA: ( COMPILATION "NAME" -- A-ADDR XT; RUN-TIME X1 X2 -- ) gforth-1.0: Locals definition words.
                                                            (line 11631)
* dabs ( D -- UD ) double:               Double precision.  (line  3853)
* dark-mode ( -- ) gforth-1.0:           Terminal output.   (line 10865)
* darshift ( D1 U -- D2 ) gforth-1.0:    Bitwise operations.
                                                            (line  4160)
* dbg ( "NAME" -- ) gforth-0.2:          Singlestep Debugger.
                                                            (line 14537)
* debug-fid ( -- FILE-ID ) gforth-1.0:   Debugging.         (line 14357)
* dec. ( N -- ) gforth-0.2:              Simple numeric output.
                                                            (line 10420)
* dec.r ( U N -- ) gforth-0.5:           Simple numeric output.
                                                            (line 10438)
* decimal ( -- ) core:                   Number Conversion. (line  8864)
* default-color ( -- ) gforth-1.0:       Terminal output.   (line 10829)
* default-w: ( -- ) gforth-experimental: Gforth locals.     (line 11553)
* default-wa: ( -- ) gforth-experimental: Gforth locals.    (line 11549)
* Defer ( "NAME" -- ) core-ext:          Deferred Words.    (line  7854)
* defer ( -- ) oof:                      Class Declaration. (line 13454)
* defer! ( XT XT-DEFERRED -- ) core-ext: Deferred Words.    (line  7858)
* defer@ ( XT-DEFERRED -- XT ) core-ext: Deferred Words.    (line  7864)
* defers ( COMPILATION "NAME" -- ; RUN-TIME ... -- ... ) gforth-0.2: Deferred Words.
                                                            (line  7874)
* definer! ( DEFINER XT -- ) gforth-obsolete: Threading Words.
                                                            (line 16514)
* defines ( XT CLASS "NAME" -- ) mini-oof: Basic Mini-OOF Usage.
                                                            (line 13512)
* definitions ( -- ) search:             Word Lists.        (line  9358)
* defocus ( -- ) minos2:                 actor methods.     (line 19061)
* delete ( BUFFER SIZE U -- ) gforth-0.7: Memory Blocks.    (line  5231)
* delete-file ( C-ADDR U -- WIOR ) file: General files.     (line  9919)
* delta-i ( R:ULIMIT R:U -- R:ULIMIT R:U U2 ) gforth-1.0: Counted Loops.
                                                            (line  6055)
* depth ( -- +N ) core:                  Examining data.    (line 14258)
* df! ( R DF-ADDR -- ) floating-ext:     Memory Access.     (line  4914)
* df@ ( DF-ADDR -- R ) floating-ext:     Memory Access.     (line  4910)
* dfalign ( -- ) floating-ext:           Dictionary allocation.
                                                            (line  4784)
* dfaligned ( C-ADDR -- DF-ADDR ) floating-ext: Address arithmetic.
                                                            (line  5137)
* dffield: ( U1 "NAME" -- U2 ) floating-ext: Forth200x Structures.
                                                            (line 12510)
* dfloat% ( -- ALIGN SIZE ) gforth-0.4:  Structure Glossary.
                                                            (line 12419)
* dfloat+ ( DF-ADDR1 -- DF-ADDR2 ) floating-ext: Address arithmetic.
                                                            (line  5132)
* dfloat/ ( N1 -- N2 ) gforth-1.0:       Address arithmetic.
                                                            (line  5135)
* dfloats ( N1 -- N2 ) floating-ext:     Address arithmetic.
                                                            (line  5128)
* dglue ( -- RTYP RSUB RADD ) minos2:    widget methods.    (line 19154)
* dglue@ ( -- RTYP RSUB RADD ) minos2:   widget methods.    (line 19163)
* dict-new ( ... CLASS -- OBJECT ) objects: Objects Glossary.
                                                            (line 13147)
* dirname ( C-ADDR1 U1 -- C-ADDR1 U2 ) gforth-0.7: Directories.
                                                            (line 10041)
* discode ( ADDR U -- ) gforth-0.2:      Common Disassembler.
                                                            (line 15571)
* dispose-widget ( -- ) minos2:          widget methods.    (line 19181)
* dlshift ( UD1 U -- UD2 ) gforth-1.0:   Bitwise operations.
                                                            (line  4153)
* dmax ( D1 D2 -- D ) double:            Double precision.  (line  3857)
* dmin ( D1 D2 -- D ) double:            Double precision.  (line  3855)
* dnegate ( D1 -- D2 ) double:           Double precision.  (line  3851)
* DO ( COMPILATION -- DO-SYS ; RUN-TIME W1 W2 -- LOOP-SYS ) core: Counted Loops.
                                                            (line  6025)
* doabicode, ( -- ) gforth-1.0:          Threading Words.   (line 16428)
* doabicode: ( -- ADDR ) gforth-1.0:     Threading Words.   (line 16481)
* docol, ( -- ) gforth-1.0:              Threading Words.   (line 16407)
* docol: ( -- ADDR ) gforth-0.2:         Threading Words.   (line 16457)
* docon, ( -- ) gforth-1.0:              Threading Words.   (line 16410)
* docon: ( -- ADDR ) gforth-0.2:         Threading Words.   (line 16460)
* dodefer, ( -- ) gforth-1.0:            Threading Words.   (line 16419)
* dodefer: ( -- ADDR ) gforth-0.2:       Threading Words.   (line 16469)
* dodoes: ( -- ADDR ) gforth-0.6:        Threading Words.   (line 16478)
* does-code! ( XT2 XT1 -- ) gforth-0.2:  Threading Words.   (line 16501)
* DOES> ( COMPILATION COLON-SYS1 -- COLON-SYS2 ) core: CREATE..DOES> details.
                                                            (line  7332)
* dofield, ( -- ) gforth-1.0:            Threading Words.   (line 16422)
* dofield: ( -- ADDR ) gforth-0.2:       Threading Words.   (line 16472)
* DONE ( COMPILATION DO-SYS -- ; RUN-TIME -- ) gforth-0.2: Counted Loops.
                                                            (line  6066)
* double% ( -- ALIGN SIZE ) gforth-0.4:  Structure Glossary.
                                                            (line 12421)
* douser, ( -- ) gforth-1.0:             Threading Words.   (line 16416)
* douser: ( -- ADDR ) gforth-0.2:        Threading Words.   (line 16466)
* dovalue, ( -- ) gforth-1.0:            Threading Words.   (line 16425)
* dovalue: ( -- ADDR ) gforth-0.7:       Threading Words.   (line 16475)
* dovar, ( -- ) gforth-1.0:              Threading Words.   (line 16413)
* dovar: ( -- ADDR ) gforth-0.2:         Threading Words.   (line 16463)
* dpl ( -- A-ADDR ) gforth-0.2:          Number Conversion. (line  8868)
* draw ( -- ) minos2:                    widget methods.    (line 19142)
* draw-init ( -- ) minos2:               widget methods.    (line 19139)
* drol ( UD1 U -- UD2 ) gforth-1.0:      Bitwise operations.
                                                            (line  4220)
* drop ( W -- ) core:                    Data stack.        (line  4520)
* dror ( UD1 U -- UD2 ) gforth-1.0:      Bitwise operations.
                                                            (line  4223)
* drshift ( UD1 U -- UD2 ) gforth-1.0:   Bitwise operations.
                                                            (line  4156)
* du/mod ( D U -- N U1 ) gforth-1.0:     Integer division.  (line  3953)
* du< ( UD1 UD2 -- F ) double-ext:       Numeric comparison.
                                                            (line  4297)
* du<= ( UD1 UD2 -- F ) gforth-0.2:      Numeric comparison.
                                                            (line  4299)
* du> ( UD1 UD2 -- F ) gforth-0.2:       Numeric comparison.
                                                            (line  4301)
* du>= ( UD1 UD2 -- F ) gforth-0.2:      Numeric comparison.
                                                            (line  4303)
* dump ( ADDR U -- ) tools:              Examining data.    (line 14280)
* dup ( W -- W W ) core:                 Data stack.        (line  4524)
* D^ ( COMPILATION "NAME" -- A-ADDR XT; RUN-TIME X1 X2 -- ) gforth-0.2: Locals definition words.
                                                            (line 11634)
* early ( -- ) oof:                      Class Declaration. (line 13459)
* edit ( "NAME" -- ) gforth-1.0:         Locating source code definitions.
                                                            (line 14033)
* edit-line ( C-ADDR N1 N2 -- N3 ) gforth-0.6: Line input and conversion.
                                                            (line 11074)
* ekey ( -- U ) facility-ext:            Single-key input.  (line 10915)
* ekey>char ( U -- U FALSE | C TRUE ) facility-ext: Single-key input.
                                                            (line 10921)
* ekey>fkey ( U1 -- U2 F ) facility-ext: Single-key input.  (line 10926)
* ekey>xchar ( U -- U FALSE | XC TRUE ) xchar-ext: Single-key input.
                                                            (line 10918)
* ekey? ( -- FLAG ) facility-ext:        Single-key input.  (line 10930)
* ekeyed ( EKEY -- ) minos2:             actor methods.     (line 19052)
* ELSE ( COMPILATION ORIG1 -- ORIG2 ; RUN-TIME -- ) core: Arbitrary control structures.
                                                            (line  6268)
* emit ( C -- ) core:                    Displaying characters and strings.
                                                            (line 10789)
* emit-file ( C WFILEID -- WIOR ) gforth-0.2: General files.
                                                            (line  9962)
* empty-buffer ( BUFFER -- ) gforth-0.2: Blocks.            (line 10351)
* empty-buffers ( -- ) block-ext:        Blocks.            (line 10347)
* end-c-library ( -- ) gforth-0.7:       Defining library interfaces.
                                                            (line 15167)
* end-class ( ALIGN OFFSET "NAME" -- ) objects: Objects Glossary.
                                                            (line 13150)
* end-class ( CLASS SELECTORS VARS "NAME" -- ) mini-oof: Basic Mini-OOF Usage.
                                                            (line 13509)
* end-class-noname ( ALIGN OFFSET -- CLASS ) objects: Objects Glossary.
                                                            (line 13154)
* end-code ( COLON-SYS -- ) gforth-0.2:  Assembler Definitions.
                                                            (line 15421)
* end-interface ( "NAME" -- ) objects:   Objects Glossary.  (line 13157)
* end-interface-noname ( -- INTERFACE ) objects: Objects Glossary.
                                                            (line 13161)
* end-methods ( -- ) objects:            Objects Glossary.  (line 13164)
* end-struct ( ALIGN SIZE "NAME" -- ) gforth-0.2: Structure Glossary.
                                                            (line 12423)
* end-structure ( STRUCT-SYS +N -- ) facility-ext: Forth200x Structures.
                                                            (line 12488)
* endcase ( COMPILATION CASE-SYS -- ; RUN-TIME X -- ) core-ext: Arbitrary control structures.
                                                            (line  6300)
* ENDIF ( COMPILATION ORIG -- ; RUN-TIME -- ) gforth-0.2: Arbitrary control structures.
                                                            (line  6285)
* endof ( COMPILATION CASE-SYS1 OF-SYS -- CASE-SYS2 ; RUN-TIME -- ) core-ext: Arbitrary control structures.
                                                            (line  6317)
* endscope ( COMPILATION SCOPE -- ; RUN-TIME -- ) gforth-0.2: Where are locals visible by name?.
                                                            (line 11676)
* endtry ( COMPILATION -- ; RUN-TIME R:SYS1 -- ) gforth-0.5: Exception Handling.
                                                            (line  6547)
* endtry-iferror ( COMPILATION ORIG1 -- ORIG2 ; RUN-TIME R:SYS1 -- ) gforth-0.7: Exception Handling.
                                                            (line  6626)
* entered ( -- ) minos2:                 actor methods.     (line 19064)
* environment ( -- ) gforth-0.6:         Environmental Queries.
                                                            (line  9749)
* environment-wordlist ( -- WID ) gforth-0.2: Environmental Queries.
                                                            (line  9745)
* environment? ( C-ADDR U -- FALSE / ... TRUE ) core: Environmental Queries.
                                                            (line  9598)
* erase ( ADDR U -- ) core-ext:          Memory Blocks.     (line  5221)
* error-color ( -- ) gforth-1.0:         Terminal output.   (line 10832)
* error-hl-inv ( -- ) gforth-1.0:        Terminal output.   (line 10835)
* error-hl-ul ( -- ) gforth-1.0:         Terminal output.   (line 10838)
* evaluate ( ... ADDR U -- ... ) core,block: Input Sources. (line  8824)
* event-loop ( -- ) gforth-experimental: Message queues.    (line 14856)
* exception ( ADDR U -- N ) gforth-0.2:  Exception Handling.
                                                            (line  6450)
* exceptions ( XT N1 -- N2 ) gforth-1.0: Exception Handling.
                                                            (line  6460)
* execute ( XT -- ) core:                Execution token.   (line  8165)
* execute-exit ( COMPILATION -- ; RUN-TIME XT NEST-SYS -- ) gforth-1.0: Execution token.
                                                            (line  8168)
* execute-parsing ( ... ADDR U XT -- ... ) gforth-0.6: The Input Stream.
                                                            (line  9307)
* execute-parsing-file ( I*X FILEID XT -- J*X ) gforth-0.6: The Input Stream.
                                                            (line  9323)
* execute-task ( XT -- TASK ) gforth-experimental: Basic multi-tasking.
                                                            (line 14689)
* EXIT ( COMPILATION -- ; RUN-TIME NEST-SYS -- ) core: Calls and returns.
                                                            (line  6406)
* exitm ( -- ) objects:                  Objects Glossary.  (line 13168)
* expand-where ( -- ) gforth-1.0:        Locating uses of a word.
                                                            (line 14084)
* expect ( C-ADDR +N -- ) core-ext-obsolescent: Line input and conversion.
                                                            (line 11120)
* extend-mem ( ADDR1 U1 U -- ADDR ADDR2 U2 ) gforth-experimental: Heap Allocation.
                                                            (line  4838)
* extend-structure ( N "NAME" -- STRUCT-SYS N ) gforth-1.0: Forth200x Structures.
                                                            (line 12484)
* f! ( R F-ADDR -- ) floating:           Memory Access.     (line  4899)
* f* ( R1 R2 -- R3 ) floating:           Floating Point.    (line  4340)
* f** ( R1 R2 -- R3 ) floating-ext:      Floating Point.    (line  4365)
* f+ ( R1 R2 -- R3 ) floating:           Floating Point.    (line  4336)
* f, ( F -- ) gforth-0.2:                Dictionary allocation.
                                                            (line  4734)
* f- ( R1 R2 -- R3 ) floating:           Floating Point.    (line  4338)
* f-rot ( R1 R2 R3 -- R3 R1 R2 ) floating: Floating point stack.
                                                            (line  4587)
* f. ( R -- ) floating-ext:              Floating-point output.
                                                            (line 10614)
* f.rdp ( RF +NR +ND +NP -- ) gforth-0.6: Floating-point output.
                                                            (line 10650)
* f.s ( -- ) gforth-0.2:                 Examining data.    (line 14239)
* f.s-precision ( -- U ) gforth-1.0:     Examining data.    (line 14244)
* f/ ( R1 R2 -- R3 ) floating:           Floating Point.    (line  4342)
* f0< ( R -- F ) floating:               Floating Point.    (line  4471)
* f0<= ( R -- F ) gforth-0.2:            Floating Point.    (line  4473)
* f0<> ( R -- F ) gforth-0.2:            Floating Point.    (line  4475)
* f0= ( R -- F ) floating:               Floating Point.    (line  4477)
* f0> ( R -- F ) gforth-0.2:             Floating Point.    (line  4479)
* f0>= ( R -- F ) gforth-0.2:            Floating Point.    (line  4481)
* f2* ( R1 -- R2 ) gforth-0.2:           Floating Point.    (line  4386)
* f2/ ( R1 -- R2 ) gforth-0.2:           Floating Point.    (line  4389)
* F: ( COMPILATION "NAME" -- A-ADDR XT; RUN-TIME R -- ) gforth-0.2: Locals definition words.
                                                            (line 11646)
* f< ( R1 R2 -- F ) floating:            Floating Point.    (line  4463)
* f<= ( R1 R2 -- F ) gforth-0.2:         Floating Point.    (line  4465)
* f<> ( R1 R2 -- F ) gforth-0.2:         Floating Point.    (line  4461)
* f= ( R1 R2 -- F ) gforth-0.2:          Floating Point.    (line  4459)
* f> ( R1 R2 -- F ) gforth-0.2:          Floating Point.    (line  4467)
* f>= ( R1 R2 -- F ) gforth-0.2:         Floating Point.    (line  4469)
* f>buf-rdp ( RF C-ADDR +NR +ND +NP -- ) gforth-0.6: Floating-point output.
                                                            (line 10695)
* f>d ( R -- D ) floating:               Floating Point.    (line  4332)
* f>l ( R -- ) gforth-0.2:               Locals implementation.
                                                            (line 11944)
* f>s ( R -- N ) floating-ext:           Floating Point.    (line  4330)
* f>str-rdp ( RF +NR +ND +NP -- C-ADDR NR ) gforth-0.6: Floating-point output.
                                                            (line 10689)
* f@ ( F-ADDR -- R ) floating:           Memory Access.     (line  4896)
* f@localn ( NOFFSET -- R ) gforth-1.0:  Locals implementation.
                                                            (line 11934)
* FA: ( COMPILATION "NAME" -- A-ADDR XT; RUN-TIME F -- ) gforth-1.0: Locals definition words.
                                                            (line 11649)
* fabs ( R1 -- R2 ) floating-ext:        Floating Point.    (line  4346)
* facos ( R1 -- R2 ) floating-ext:       Floating Point.    (line  4419)
* facosh ( R1 -- R2 ) floating-ext:      Floating Point.    (line  4435)
* fade-color: ( RGBA1 RGBA2 "NAME" -- ) minos2: widget methods.
                                                            (line 19224)
* falign ( -- ) floating:                Dictionary allocation.
                                                            (line  4776)
* faligned ( C-ADDR -- F-ADDR ) floating: Address arithmetic.
                                                            (line  5111)
* falog ( R1 -- R2 ) floating-ext:       Floating Point.    (line  4383)
* false ( -- F ) core-ext:               Boolean Flags.     (line  3765)
* fasin ( R1 -- R2 ) floating-ext:       Floating Point.    (line  4417)
* fasinh ( R1 -- R2 ) floating-ext:      Floating Point.    (line  4433)
* fast-throw ( ... WBALL -- ... WBALL ) gforth-experimental: Exception Handling.
                                                            (line  6430)
* fatan ( R1 -- R2 ) floating-ext:       Floating Point.    (line  4421)
* fatan2 ( R1 R2 -- R3 ) floating-ext:   Floating Point.    (line  4423)
* fatanh ( R1 -- R2 ) floating-ext:      Floating Point.    (line  4437)
* faxpy ( RA F-X NSTRIDEX F-Y NSTRIDEY UCOUNT -- ) gforth-0.5: Floating Point.
                                                            (line  4402)
* fclearstack ( R0 .. RN -- ) gforth-1.0: Examining data.   (line 14269)
* fconstant ( R "NAME" -- ) floating:    Constants.         (line  6822)
* fcopysign ( R1 R2 -- R3 ) gforth-1.0:  Floating Point.    (line  4348)
* fcos ( R1 -- R2 ) floating-ext:        Floating Point.    (line  4410)
* fcosh ( R1 -- R2 ) floating-ext:       Floating Point.    (line  4429)
* fdepth ( -- +N ) floating:             Examining data.    (line 14262)
* fdrop ( R -- ) floating:               Floating point stack.
                                                            (line  4566)
* fdup ( R -- R R ) floating:            Floating point stack.
                                                            (line  4570)
* fe. ( R -- ) floating-ext:             Floating-point output.
                                                            (line 10618)
* fexp ( R1 -- R2 ) floating-ext:        Floating Point.    (line  4370)
* fexpm1 ( R1 -- R2 ) floating-ext:      Floating Point.    (line  4372)
* ffield: ( U1 "NAME" -- U2 ) floating-ext: Forth200x Structures.
                                                            (line 12504)
* ffourth ( R1 R2 R3 R4 -- R1 R2 R3 R4 R1 ) gforth-1.0: Floating point stack.
                                                            (line  4576)
* field ( ALIGN1 OFFSET1 ALIGN SIZE "NAME" -- ALIGN2 OFFSET2 ) gforth-0.2: Structure Glossary.
                                                            (line 12428)
* field: ( U1 "NAME" -- U2 ) facility-ext: Forth200x Structures.
                                                            (line 12498)
* file-eof? ( WFILEID -- FLAG ) gforth-0.6: General files.  (line  9955)
* file-position ( WFILEID -- UD WIOR ) file: General files. (line  9968)
* file-size ( WFILEID -- UD WIOR ) file: General files.     (line  9972)
* file-status ( C-ADDR U -- WFAM WIOR ) file-ext: General files.
                                                            (line  9966)
* file>fpath ( ADDR1 U1 -- ADDR2 U2 ) gforth-1.0: Source Search Paths.
                                                            (line 10133)
* file>path ( C-ADDR1 U1 PATH-ADDR -- C-ADDR2 U2 ) gforth-1.0: General Search Paths.
                                                            (line 10158)
* filename-match ( C-ADDR1 U1 C-ADDR2 U2 -- FLAG ) gforth-0.5: Directories.
                                                            (line 10067)
* fill ( C-ADDR U C -- ) core:           Memory Blocks.     (line  5218)
* find ( C-ADDR -- XT +-1 | C-ADDR 0 ) core,search: Word Lists.
                                                            (line  9424)
* find-name ( C-ADDR U -- NT | 0 ) gforth-0.2: Name token.  (line  8205)
* find-name-in ( C-ADDR U WID -- NT | 0 ) gforth-1.0: Name token.
                                                            (line  8209)
* fkey. ( U -- ) gforth-1.0:             Single-key input.  (line 11049)
* FLiteral ( COMPILATION R -- ; RUN-TIME -- R ) floating: Literals.
                                                            (line  8399)
* fln ( R1 -- R2 ) floating-ext:         Floating Point.    (line  4375)
* flnp1 ( R1 -- R2 ) floating-ext:       Floating Point.    (line  4377)
* float ( -- U ) gforth-0.3:             Address arithmetic.
                                                            (line  5105)
* float% ( -- ALIGN SIZE ) gforth-0.4:   Structure Glossary.
                                                            (line 12435)
* float+ ( F-ADDR1 -- F-ADDR2 ) floating: Address arithmetic.
                                                            (line  5102)
* float/ ( N1 -- N2 ) gforth-1.0:        Address arithmetic.
                                                            (line  5109)
* floating-stack ( -- N ) environment:   Environmental Queries.
                                                            (line  9656)
* floats ( N1 -- N2 ) floating:          Address arithmetic.
                                                            (line  5099)
* flog ( R1 -- R2 ) floating-ext:        Floating Point.    (line  4380)
* floor ( R1 -- R2 ) floating:           Floating Point.    (line  4355)
* FLOORED ( -- F ) environment:          Environmental Queries.
                                                            (line  9635)
* flush ( -- ) block:                    Blocks.            (line 10366)
* flush-file ( WFILEID -- WIOR ) file-ext: General files.   (line  9964)
* flush-icache ( C-ADDR U -- ) gforth-0.2: Assembler Definitions.
                                                            (line 15438)
* fm/mod ( D1 N1 -- N2 N3 ) core:        Integer division.  (line  3944)
* fmax ( R1 R2 -- R3 ) floating:         Floating Point.    (line  4351)
* fmin ( R1 R2 -- R3 ) floating:         Floating Point.    (line  4353)
* fnegate ( R1 -- R2 ) floating:         Floating Point.    (line  4344)
* fnip ( R1 R2 -- R2 ) gforth-0.2:       Floating point stack.
                                                            (line  4568)
* focus ( -- ) minos2:                   actor methods.     (line 19058)
* FOR ( COMPILATION -- DO-SYS ; RUN-TIME U -- LOOP-SYS ) gforth-0.2: Counted Loops.
                                                            (line  6028)
* FORK ( COMPILATION -- ORIG ; RUN-TIME F -- ) gforth-0.7: Regular Expressions.
                                                            (line 13796)
* form ( -- NLINES NCOLS ) gforth-0.2:   Terminal output.   (line 10812)
* Forth ( -- ) search-ext:               Word Lists.        (line  9405)
* forth-recognize ( C-ADDR U -- ... TRANSLATE-XT ) recognizer: Dealing with existing Recognizers.
                                                            (line  9176)
* forth-recognizer ( -- XT ) gforth-experimental: Dealing with existing Recognizers.
                                                            (line  9179)
* forth-wordlist ( -- WID ) search:      Word Lists.        (line  9353)
* forward ( "NAME" -- ) gforth-1.0:      Forward.           (line  7893)
* fourth ( W1 W2 W3 W4 -- W1 W2 W3 W4 W1 ) gforth-1.0: Data stack.
                                                            (line  4530)
* fover ( R1 R2 -- R1 R2 R1 ) floating:  Floating point stack.
                                                            (line  4572)
* fp! ( F-ADDR -- F:... ) gforth-0.2:    Stack pointer manipulation.
                                                            (line  4640)
* fp. ( R -- ) floating-ext:             Floating-point output.
                                                            (line 10626)
* fp0 ( -- A-ADDR ) gforth-0.4:          Stack pointer manipulation.
                                                            (line  4635)
* fp@ ( F:... -- F-ADDR ) gforth-0.2:    Stack pointer manipulation.
                                                            (line  4638)
* fpath ( -- PATH-ADDR ) gforth-0.4:     Source Search Paths.
                                                            (line 10128)
* fpick ( F:... U -- F:... R ) gforth-0.4: Floating point stack.
                                                            (line  4582)
* free ( A_ADDR -- WIOR ) memory:        Heap Allocation.   (line  4815)
* free-closure ( XT -- ) gforth-internal: Closures.         (line 12093)
* free-mem-var ( ADDR -- ) gforth-experimental: Heap Allocation.
                                                            (line  4834)
* frot ( R1 R2 R3 -- R2 R3 R1 ) floating: Floating point stack.
                                                            (line  4585)
* fround ( R1 -- R2 ) floating:          Floating Point.    (line  4359)
* fs. ( R -- ) floating-ext:             Floating-point output.
                                                            (line 10622)
* fsin ( R1 -- R2 ) floating-ext:        Floating Point.    (line  4408)
* fsincos ( R1 -- R2 R3 ) floating-ext:  Floating Point.    (line  4412)
* fsinh ( R1 -- R2 ) floating-ext:       Floating Point.    (line  4427)
* fsqrt ( R1 -- R2 ) floating-ext:       Floating Point.    (line  4368)
* fswap ( R1 R2 -- R2 R1 ) floating:     Floating point stack.
                                                            (line  4580)
* ftan ( R1 -- R2 ) floating-ext:        Floating Point.    (line  4415)
* ftanh ( R1 -- R2 ) floating-ext:       Floating Point.    (line  4431)
* fthird ( R1 R2 R3 -- R1 R2 R3 R1 ) gforth-1.0: Floating point stack.
                                                            (line  4574)
* ftrunc ( R1 -- R2 ) floating-ext:      Floating Point.    (line  4362)
* ftuck ( R1 R2 -- R2 R1 R2 ) gforth-0.2: Floating point stack.
                                                            (line  4578)
* fvalue ( R "NAME" -- ) floating-ext:   Values.            (line  6889)
* fvariable ( "NAME" -- ) floating:      Variables.         (line  6781)
* fvarue ( R "NAME" -- ) gforth-1.0:     Varues.            (line  6915)
* F^ ( COMPILATION "NAME" -- A-ADDR XT; RUN-TIME R -- ) gforth-0.2: Locals definition words.
                                                            (line 11652)
* f~ ( R1 R2 R3 -- FLAG ) floating-ext:  Floating Point.    (line  4455)
* f~abs ( R1 R2 R3 -- FLAG ) gforth-0.5: Floating Point.    (line  4452)
* f~rel ( R1 R2 R3 -- FLAG ) gforth-0.5: Floating Point.    (line  4449)
* g ( -- ) gforth-0.7:                   Locating source code definitions.
                                                            (line 14017)
* gap ( -- R ) minos2:                   widget methods.    (line 19112)
* get ( -- SOMETHING ) minos2:           actor methods.     (line 19076)
* get-block-fid ( -- WFILEID ) gforth-0.2: Blocks.          (line 10316)
* get-current ( -- WID ) search:         Word Lists.        (line  9362)
* get-dir ( C-ADDR1 U1 -- C-ADDR2 U2 ) gforth-0.7: Directories.
                                                            (line 10072)
* get-order ( -- WIDN .. WID1 N ) search: Word Lists.       (line  9368)
* get-recognizers ( -- XT1 .. XTN N ) gforth-experimental: Dealing with existing Recognizers.
                                                            (line  9163)
* getenv ( C-ADDR1 U1 -- C-ADDR2 U2 ) gforth-0.2: Passing Commands to the OS.
                                                            (line 16549)
* gforth ( -- C-ADDR U ) gforth-environment: Environmental Queries.
                                                            (line  9722)
* gg ( -- ) gforth-1.0:                  Locating uses of a word.
                                                            (line 14066)
* h ( -- R ) minos2:                     widget methods.    (line 19106)
* halt ( TASK -- ) gforth-experimental:  Basic multi-tasking.
                                                            (line 14705)
* heap-new ( ... CLASS -- OBJECT ) objects: Objects Glossary.
                                                            (line 13171)
* help ( "REST-OF-LINE" -- ) gforth-1.0: Help on Gforth.    (line   707)
* here ( -- ADDR ) core:                 Dictionary allocation.
                                                            (line  4714)
* hex ( -- ) core-ext:                   Number Conversion. (line  8860)
* hglue ( -- RTYP RSUB RADD ) minos2:    widget methods.    (line 19151)
* hglue@ ( -- RTYP RSUB RADD ) minos2:   widget methods.    (line 19160)
* hide ( -- ) minos2:                    actor methods.     (line 19073)
* hmcopy, ( XT -- ) gforth-experimental: Threading Words.   (line 16403)
* hold ( CHAR -- ) core:                 Formatted numeric output.
                                                            (line 10517)
* holds ( ADDR U -- ) core-ext:          Formatted numeric output.
                                                            (line 10521)
* how: ( -- ) oof:                       Class Declaration. (line 13472)
* i ( R:N -- R:N N ) core:               Counted Loops.     (line  6043)
* i' ( R:W R:W2 -- R:W R:W2 W ) gforth-0.2: Counted Loops.  (line  6052)
* id. ( NT -- ) gforth-0.6:              Name token.        (line  8250)
* IF ( COMPILATION -- ORIG ; RUN-TIME F -- ) core: Arbitrary control structures.
                                                            (line  6226)
* iferror ( COMPILATION ORIG1 -- ORIG2 ; RUN-TIME -- ) gforth-0.7: Exception Handling.
                                                            (line  6550)
* immediate ( -- ) core:                 Interpretation and Compilation Semantics.
                                                            (line  7987)
* immediate? ( NT -- FLAG ) gforth-1.0:  Header methods.    (line 16359)
* implementation ( INTERFACE -- ) objects: Objects Glossary.
                                                            (line 13174)
* include ( ... "FILE" -- ... ) file-ext: Forth source files.
                                                            (line  9855)
* include-file ( I*X WFILEID -- J*X ) file: Forth source files.
                                                            (line  9841)
* include-locale ( "NAME" -- ) gforth-experimental: i18n and l10n.
                                                            (line 11324)
* included ( I*X C-ADDR U -- J*X ) file: Forth source files.
                                                            (line  9845)
* included-locale ( ADDR U -- ) gforth-experimental: i18n and l10n.
                                                            (line 11321)
* included? ( C-ADDR U -- F ) gforth-0.2: Forth source files.
                                                            (line  9848)
* infile-execute ( ... XT FILE-ID -- ... ) gforth-0.7: Redirection.
                                                            (line 10017)
* infile-id ( -- FILE-ID ) gforth-0.4:   Redirection.       (line 10020)
* infinity ( -- R ) gforth-1.0:          Floating Point.    (line  4487)
* info-color ( -- ) gforth-1.0:          Terminal output.   (line 10844)
* init-asm ( -- ) gforth-0.2:            Assembler Definitions.
                                                            (line 15399)
* init-buffer ( ADDR -- ) gforth-experimental: Heap Allocation.
                                                            (line  4854)
* init-object ( ... CLASS OBJECT -- ) objects: Objects Glossary.
                                                            (line 13178)
* initiate ( XT TASK -- ) gforth-experimental: Basic multi-tasking.
                                                            (line 14664)
* inline: ( "NAME" -- INLINE:-SYS ) gforth-experimental: Colon Definitions.
                                                            (line  6944)
* input-color ( -- ) gforth-1.0:         Terminal output.   (line 10850)
* insert ( STRING LENGTH BUFFER SIZE -- ) gforth-0.7: Memory Blocks.
                                                            (line  5227)
* inst-value ( ALIGN1 OFFSET1 "NAME" -- ALIGN2 OFFSET2 ) objects: Objects Glossary.
                                                            (line 13182)
* inst-var ( ALIGN1 OFFSET1 ALIGN SIZE "NAME" -- ALIGN2 OFFSET2 ) objects: Objects Glossary.
                                                            (line 13186)
* INT-[I] ( -- N ) gforth-1.0:           Interpreter Directives.
                                                            (line  8979)
* interface ( -- ) objects:              Objects Glossary.  (line 13190)
* interpret ( ... -- ... ) gforth-0.2:   The Text Interpreter.
                                                            (line  8766)
* interpret/compile: ( INTERP-XT COMP-XT "NAME" -- ) gforth-0.2: Combined words.
                                                            (line  8020)
* invert ( W1 -- W2 ) core:              Bitwise operations.
                                                            (line  4135)
* IS ( VALUE "NAME" -- ) core-ext:       Deferred Words.    (line  7861)
* j ( R:N R:W1 R:W2 -- N R:N R:W1 R:W2 ) core: Counted Loops.
                                                            (line  6046)
* JOIN ( ORIG -- ) gforth-0.7:           Regular Expressions.
                                                            (line 13799)
* k ( R:N R:W1 R:W2 R:W3 R:W4 -- N R:N R:W1 R:W2 R:W3 R:W4 ) gforth-0.3: Counted Loops.
                                                            (line  6049)
* k-alt-mask ( -- U ) facility-ext:      Single-key input.  (line 10994)
* k-backspace ( -- U ) gforth-1.0:       Single-key input.  (line 11002)
* k-ctrl-mask ( -- U ) facility-ext:     Single-key input.  (line 10992)
* k-delete ( -- U ) facility-ext:        Single-key input.  (line 10956)
* k-down ( -- U ) facility-ext:          Single-key input.  (line 10941)
* k-end ( -- U ) facility-ext:           Single-key input.  (line 10946)
* k-enter ( -- U ) gforth-1.0:           Single-key input.  (line 11000)
* k-eof ( -- U ) gforth-1.0:             Single-key input.  (line 11023)
* k-f1 ( -- U ) facility-ext:            Single-key input.  (line 10961)
* k-f10 ( -- U ) facility-ext:           Single-key input.  (line 10979)
* k-f11 ( -- U ) facility-ext:           Single-key input.  (line 10981)
* k-f12 ( -- U ) facility-ext:           Single-key input.  (line 10983)
* k-f2 ( -- U ) facility-ext:            Single-key input.  (line 10963)
* k-f3 ( -- U ) facility-ext:            Single-key input.  (line 10965)
* k-f4 ( -- U ) facility-ext:            Single-key input.  (line 10967)
* k-f5 ( -- U ) facility-ext:            Single-key input.  (line 10969)
* k-f6 ( -- U ) facility-ext:            Single-key input.  (line 10971)
* k-f7 ( -- U ) facility-ext:            Single-key input.  (line 10973)
* k-f8 ( -- U ) facility-ext:            Single-key input.  (line 10975)
* k-f9 ( -- U ) facility-ext:            Single-key input.  (line 10977)
* k-home ( -- U ) facility-ext:          Single-key input.  (line 10943)
* k-insert ( -- U ) facility-ext:        Single-key input.  (line 10954)
* k-left ( -- U ) facility-ext:          Single-key input.  (line 10935)
* k-mute ( -- U ) gforth-1.0:            Single-key input.  (line 11014)
* k-next ( -- U ) facility-ext:          Single-key input.  (line 10951)
* k-pause ( -- U ) gforth-1.0:           Single-key input.  (line 11012)
* k-prior ( -- U ) facility-ext:         Single-key input.  (line 10948)
* k-right ( -- U ) facility-ext:         Single-key input.  (line 10937)
* k-sel ( -- U ) gforth-1.0:             Single-key input.  (line 11020)
* k-shift-mask ( -- U ) facility-ext:    Single-key input.  (line 10990)
* k-tab ( -- U ) gforth-1.0:             Single-key input.  (line 11004)
* k-up ( -- U ) facility-ext:            Single-key input.  (line 10939)
* k-voldown ( -- U ) gforth-1.0:         Single-key input.  (line 11018)
* k-volup ( -- U ) gforth-1.0:           Single-key input.  (line 11016)
* k-winch ( -- U ) gforth-1.0:           Single-key input.  (line 11008)
* kerning ( -- R ) minos2:               widget methods.    (line 19118)
* key ( -- CHAR ) core:                  Single-key input.  (line 10880)
* key-file ( FD -- KEY ) gforth-0.4:     General files.     (line  9942)
* key-ior ( -- CHAR|IOR ) gforth-1.0:    Single-key input.  (line 10883)
* key? ( -- FLAG ) facility:             Single-key input.  (line 10887)
* key?-file ( WFILEID -- F ) gforth-0.4: General files.     (line  9949)
* kill ( TASK -- ) gforth-experimental:  Basic multi-tasking.
                                                            (line 14700)
* kill-task ( -- ) gforth-experimental:  Basic multi-tasking.
                                                            (line 14697)
* l ( -- ) gforth-1.0:                   Locating source code definitions.
                                                            (line 14006)
* l! ( W C-ADDR -- ) gforth-0.7:         Special Memory Accesses.
                                                            (line  4960)
* L" ( "LSID<">" -- LSID ) gforth-experimental: i18n and l10n.
                                                            (line 11290)
* l, ( L -- ) gforth-1.0:                Dictionary allocation.
                                                            (line  4747)
* l>s ( X -- N ) gforth-1.0:             Special Memory Accesses.
                                                            (line  5021)
* l@ ( C-ADDR -- U ) gforth-0.7:         Special Memory Accesses.
                                                            (line  4957)
* lalign ( -- ) gforth-1.0:              Address arithmetic.
                                                            (line  5165)
* laligned ( ADDR -- ADDR' ) gforth-1.0: Address arithmetic.
                                                            (line  5162)
* Language ( "NAME" -- ) gforth-experimental: i18n and l10n.
                                                            (line 11309)
* lastfit ( -- ) minos2:                 widget methods.    (line 19148)
* latest ( -- NT ) gforth-0.6:           Name token.        (line  8213)
* latestnt ( -- NT ) gforth-1.0:         Name token.        (line  8217)
* latestxt ( -- XT ) gforth-0.6:         Anonymous Definitions.
                                                            (line  7026)
* lbe ( U1 -- U2 ) gforth-1.0:           Special Memory Accesses.
                                                            (line  4988)
* LEAVE ( COMPILATION -- ; RUN-TIME LOOP-SYS -- ) core: Counted Loops.
                                                            (line  6058)
* left ( -- ) minos2:                    actor methods.     (line 19067)
* lfield: ( U1 "NAME" -- U2 ) gforth-1.0: Forth200x Structures.
                                                            (line 12516)
* lib-error ( -- C-ADDR U ) gforth-0.7:  Low-Level C Interface Words.
                                                            (line 15286)
* lib-sym ( C-ADDR1 U1 U2 -- U3 ) gforth-0.4: Low-Level C Interface Words.
                                                            (line 15284)
* license ( -- ) gforth-0.2:             Help on Gforth.    (line   719)
* light-mode ( -- ) gforth-1.0:          Terminal output.   (line 10862)
* line-end-hook ( -- ) gforth-0.7:       Text Interpreter Hooks.
                                                            (line  9236)
* list ( U -- ) block-ext:               Blocks.            (line 10323)
* list-size ( LIST -- U ) gforth-internal: Locals implementation.
                                                            (line 12016)
* Literal ( COMPILATION N -- ; RUN-TIME -- N ) core: Literals.
                                                            (line  8380)
* ll ( -- ) gforth-1.0:                  Locating uses of a word.
                                                            (line 14071)
* lle ( U1 -- U2 ) gforth-1.0:           Special Memory Accesses.
                                                            (line  4992)
* load ( I*X U -- J*X ) block:           Blocks.            (line 10369)
* load-cov ( -- ) gforth-experimental:   Code Coverage.     (line 14608)
* locale! ( ADDR U LSID -- ) gforth-experimental: i18n and l10n.
                                                            (line 11305)
* locale-csv ( "NAME" -- ) gforth-experimental: i18n and l10n.
                                                            (line 11327)
* locale-csv-out ( "NAME" -- ) gforth-experimental: i18n and l10n.
                                                            (line 11337)
* locale-file ( FID -- ) gforth-experimental: i18n and l10n.
                                                            (line 11318)
* locale@ ( LSID -- ADDR U ) gforth-experimental: i18n and l10n.
                                                            (line 11302)
* locate ( "NAME" -- ) gforth-1.0:       Locating source code definitions.
                                                            (line 13996)
* lock ( SEMAPHORE -- ) gforth-experimental: Semaphores.    (line 14788)
* log2 ( U -- N ) gforth-1.0:            Bitwise operations.
                                                            (line  4181)
* LOOP ( COMPILATION DO-SYS -- ; RUN-TIME LOOP-SYS1 -- | LOOP-SYS2 ) core: Counted Loops.
                                                            (line  6031)
* lp! ( C-ADDR -- ) gforth-internal:     Stack pointer manipulation.
                                                            (line  4655)
* lp! ( C-ADDR -- ) gforth-internal <1>: Locals implementation.
                                                            (line 11939)
* lp0 ( -- A-ADDR ) gforth-0.4:          Stack pointer manipulation.
                                                            (line  4649)
* lp@ ( -- C-ADDR ) gforth-0.2:          Stack pointer manipulation.
                                                            (line  4652)
* lp@ ( -- C-ADDR ) gforth-0.2 <1>:      Locals implementation.
                                                            (line 11936)
* lrol ( U1 U -- U2 ) gforth-1.0:        Bitwise operations.
                                                            (line  4206)
* lror ( U1 U -- U2 ) gforth-1.0:        Bitwise operations.
                                                            (line  4210)
* lshift ( U1 U -- U2 ) core:            Bitwise operations.
                                                            (line  4142)
* LU" ( "LSID<">" -- LSID ) gforth-experimental: i18n and l10n.
                                                            (line 11295)
* m* ( N1 N2 -- D ) core:                Mixed precision.   (line  3864)
* m*/ ( D1 N2 U3 -- DQUOT ) double:      Integer division.  (line  3990)
* m+ ( D1 N -- D2 ) double:              Mixed precision.   (line  3862)
* m: ( -- XT COLON-SYS; RUN-TIME: OBJECT -- ) objects: Objects Glossary.
                                                            (line 13193)
* macros-wordlist ( -- WID ) gforth-experimental: Substitute.
                                                            (line 11352)
* magenta-input ( -- ) gforth-1.0:       Terminal output.   (line 10871)
* make-latest ( NT -- ) gforth-1.0:      Making a word current.
                                                            (line  7735)
* map-vocs ( ... XT -- ... ) gforth-1.0: Word Lists.        (line  9488)
* marker ( "<SPACES> NAME" -- ) core-ext: Forgetting words. (line 14292)
* max ( N1 N2 -- N ) core:               Single precision.  (line  3819)
* MAX-CHAR ( -- U ) environment:         Environmental Queries.
                                                            (line  9615)
* MAX-D ( -- D ) environment:            Environmental Queries.
                                                            (line  9644)
* max-float ( -- R ) environment:        Environmental Queries.
                                                            (line  9666)
* MAX-N ( -- N ) environment:            Environmental Queries.
                                                            (line  9638)
* MAX-U ( -- U ) environment:            Environmental Queries.
                                                            (line  9641)
* MAX-UD ( -- UD ) environment:          Environmental Queries.
                                                            (line  9647)
* MAX-XCHAR ( -- XCHAR ) environment:    Environmental Queries.
                                                            (line  9677)
* maxalign ( -- ) gforth-0.2:            Dictionary allocation.
                                                            (line  4788)
* maxaligned ( ADDR1 -- ADDR2 ) gforth-0.2: Address arithmetic.
                                                            (line  5141)
* maxdepth-.s ( -- ADDR ) gforth-0.2:    Examining data.    (line 14248)
* mem+do ( COMPILATION -- W XT DO-SYS; RUN-TIME ADDR UBYTES +NSTRIDE -- ) gforth-experimental: Counted Loops.
                                                            (line  6014)
* mem, ( ADDR U -- ) gforth-0.6:         Dictionary allocation.
                                                            (line  4758)
* mem-do ( COMPILATION -- W XT DO-SYS; RUN-TIME ADDR UBYTES +NSTRIDE -- ) gforth-experimental: Counted Loops.
                                                            (line  6020)
* method ( -- ) oof:                     Class Declaration. (line 13462)
* method ( M V "NAME" -- M' V ) mini-oof: Basic Mini-OOF Usage.
                                                            (line 13500)
* method ( XT "NAME" -- ) objects:       Objects Glossary.  (line 13203)
* methods ( CLASS -- ) objects:          Objects Glossary.  (line 13207)
* min ( N1 N2 -- N ) core:               Single precision.  (line  3817)
* mkdir-parents ( C-ADDR U MODE -- IOR ) gforth-0.7: Directories.
                                                            (line 10083)
* mod ( N1 N2 -- N ) core:               Integer division.  (line  3918)
* modf ( N1 N2 -- N ) gforth-1.0:        Integer division.  (line  3923)
* modf-stage2m ( N1 A-RECI -- UMODULUS ) gforth-1.0: Two-stage integer division.
                                                            (line  4067)
* mods ( N1 N2 -- N ) gforth-1.0:        Integer division.  (line  3921)
* move ( C-FROM C-TO UCOUNT -- ) core:   Memory Blocks.     (line  5204)
* ms ( N -- ) facility-ext:              Keeping track of Time.
                                                            (line 16558)
* mux ( U1 U2 U3 -- U ) gforth-1.0:      Bitwise operations.
                                                            (line  4137)
* mwords ( ["PATTERN"] -- ) gforth-1.0:  Word Lists.        (line  9458)
* n ( -- ) gforth-1.0:                   Locating source code definitions.
                                                            (line 14009)
* n/a ( -- ) gforth-experimental:        User-defined TO and DEFER@.
                                                            (line  7537)
* n>r ( X1 .. XN N -- R:XN..X1 R:N ) tools-ext: Return stack.
                                                            (line  4615)
* name ( -- C-ADDR U ) gforth-obsolete:  The Input Stream.  (line  9278)
* name$ ( -- ADDR U ) minos2:            widget methods.    (line 19094)
* name>compile ( NT -- W XT ) tools-ext: Name token.        (line  8244)
* name>interpret ( NT -- XT ) tools-ext: Name token.        (line  8241)
* name>link ( NT1 -- NT2 / 0 ) gforth-1.0: Name token.      (line  8256)
* name>string ( NT -- ADDR U ) tools-ext: Name token.       (line  8247)
* NaN ( -- R ) gforth-1.0:               Floating Point.    (line  4493)
* native@ ( LSID -- ADDR U ) gforth-experimental: i18n and l10n.
                                                            (line 11299)
* needs ( ... "NAME" -- ... ) gforth-0.2: Forth source files.
                                                            (line  9867)
* negate ( N1 -- N2 ) core:              Single precision.  (line  3813)
* new ( CLASS -- O ) mini-oof:           Basic Mini-OOF Usage.
                                                            (line 13515)
* new-color: ( RGBA "NAME" -- ) minos2:  widget methods.    (line 19213)
* newline ( -- C-ADDR U ) gforth-0.5:    String and character literals.
                                                            (line  5371)
* newtask ( STACKSIZE -- TASK ) gforth-experimental: Basic multi-tasking.
                                                            (line 14639)
* newtask4 ( U-DATA U-RETURN U-FP U-LOCALS -- TASK ) gforth-experimental: Basic multi-tasking.
                                                            (line 14648)
* NEXT ( COMPILATION DO-SYS -- ; RUN-TIME LOOP-SYS1 -- | LOOP-SYS2 ) gforth-0.2: Counted Loops.
                                                            (line  6040)
* next-arg ( -- ADDR U ) gforth-0.7:     OS command line arguments.
                                                            (line 11405)
* next-case ( COMPILATION CASE-SYS -- ; RUN-TIME -- ) gforth-1.0: Arbitrary control structures.
                                                            (line  6306)
* nextname ( C-ADDR U -- ) gforth-0.2:   Supplying names.   (line  7084)
* nip ( W1 W2 -- W2 ) core-ext:          Data stack.        (line  4522)
* nocov[ ( -- ) gforth-1.0:              Code Coverage.     (line 14557)
* noname ( -- ) gforth-0.2:              Anonymous Definitions.
                                                            (line  7021)
* noname-from ( XT -- ) gforth-1.0:      Creating from a prototype.
                                                            (line  7715)
* noop ( -- ) gforth-0.2:                Execution token.   (line  8178)
* notfound ( STATE -- ) gforth-experimental: Dealing with existing Recognizers.
                                                            (line  9130)
* nothrow ( -- ) gforth-0.7:             Exception Handling.
                                                            (line  6504)
* nr> ( R:XN..X1 R:N -- X1 .. XN N ) tools-ext: Return stack.
                                                            (line  4617)
* ns ( D -- ) gforth-1.0:                Keeping track of Time.
                                                            (line 16560)
* nt ( -- ) gforth-1.0:                  Locating exception source.
                                                            (line 14103)
* ntime ( -- DTIME ) gforth-1.0:         Keeping track of Time.
                                                            (line 16575)
* nw ( -- ) gforth-1.0:                  Locating uses of a word.
                                                            (line 14056)
* o> ( R:C-ADDR -- ) new:                Mini-OOF2.         (line 13697)
* object ( -- A-ADDR ) mini-oof:         Basic Mini-OOF Usage.
                                                            (line 13497)
* object ( -- CLASS ) objects:           Objects Glossary.  (line 13212)
* object-' ( "NAME" -- XT ) oof:         The OOF base class.
                                                            (line 13423)
* object-: ( "NAME" -- ) oof:            The OOF base class.
                                                            (line 13389)
* object-:: ( "NAME" -- ) oof:           The OOF base class.
                                                            (line 13401)
* object-asptr ( O "NAME" -- ) oof:      The OOF base class.
                                                            (line 13393)
* object-bind ( O "NAME" -- ) oof:       The OOF base class.
                                                            (line 13412)
* object-bound ( CLASS ADDR "NAME" -- ) oof: The OOF base class.
                                                            (line 13414)
* object-class ( "NAME" -- ) oof:        The OOF base class.
                                                            (line 13366)
* object-class? ( O -- FLAG ) oof:       The OOF base class.
                                                            (line 13370)
* object-definitions ( -- ) oof:         The OOF base class.
                                                            (line 13368)
* object-dispose ( -- ) oof:             The OOF base class.
                                                            (line 13380)
* object-endwith ( -- ) oof:             The OOF base class.
                                                            (line 13434)
* object-init ( ... -- ) oof:            The OOF base class.
                                                            (line 13378)
* object-is ( XT "NAME" -- ) oof:        The OOF base class.
                                                            (line 13418)
* object-link ( "NAME" -- CLASS ADDR ) oof: The OOF base class.
                                                            (line 13416)
* object-new ( -- O ) oof:               The OOF base class.
                                                            (line 13385)
* object-new[] ( N -- O ) oof:           The OOF base class.
                                                            (line 13387)
* object-postpone ( "NAME" -- ) oof:     The OOF base class.
                                                            (line 13425)
* object-ptr ( "NAME" -- ) oof:          The OOF base class.
                                                            (line 13391)
* object-self ( -- O ) oof:              The OOF base class.
                                                            (line 13407)
* object-super ( "NAME" -- ) oof:        The OOF base class.
                                                            (line 13403)
* object-with ( O -- ) oof:              The OOF base class.
                                                            (line 13432)
* object-[] ( N "NAME" -- ) oof:         The OOF base class.
                                                            (line 13395)
* of ( COMPILATION -- OF-SYS ; RUN-TIME X1 X2 -- |X1 ) core-ext: Arbitrary control structures.
                                                            (line  6310)
* off ( A-ADDR -- ) gforth-0.2:          Boolean Flags.     (line  3771)
* on ( A-ADDR -- ) gforth-0.2:           Boolean Flags.     (line  3768)
* once ( -- ) gforth-1.0:                Debugging.         (line 14365)
* Only ( -- ) search-ext:                Word Lists.        (line  9409)
* open-blocks ( C-ADDR U -- ) gforth-0.2: Blocks.           (line 10304)
* open-dir ( C-ADDR U -- WDIRID WIOR ) gforth-0.5: Directories.
                                                            (line 10049)
* open-file ( C-ADDR U WFAM -- WFILEID WIOR ) file: General files.
                                                            (line  9913)
* open-lib ( C-ADDR1 U1 -- U2 ) gforth-0.4: Low-Level C Interface Words.
                                                            (line 15282)
* open-path-file ( ADDR1 U1 PATH-ADDR -- WFILEID ADDR2 U2 0 | IOR ) gforth-0.2: General Search Paths.
                                                            (line 10152)
* open-pipe ( C-ADDR U WFAM -- WFILEID WIOR ) gforth-0.2: Pipes.
                                                            (line 11139)
* opt: ( COMPILATION -- COLON-SYS2 ; RUN-TIME -- NEST-SYS ) gforth-1.0: User-defined compile-comma.
                                                            (line  7580)
* or ( W1 W2 -- W ) core:                Bitwise operations.
                                                            (line  4131)
* order ( -- ) search-ext:               Word Lists.        (line  9413)
* os-class ( -- C-ADDR U ) gforth-environment: Environmental Queries.
                                                            (line  9727)
* os-type ( -- C-ADDR U ) gforth-environment: Environmental Queries.
                                                            (line  9731)
* out ( -- ADDR ) gforth-1.0:            Miscellaneous output.
                                                            (line 10722)
* outfile-execute ( ... XT FILE-ID -- ... ) gforth-0.7: Redirection.
                                                            (line 10009)
* outfile-id ( -- FILE-ID ) gforth-0.2:  Redirection.       (line 10012)
* over ( W1 W2 -- W1 W2 W1 ) core:       Data stack.        (line  4526)
* overrides ( XT "SELECTOR" -- ) objects: Objects Glossary. (line 13215)
* pad ( -- C-ADDR ) core-ext:            Memory Blocks.     (line  5241)
* page ( -- ) facility:                  Terminal output.   (line 10816)
* par-split ( RW -- ) minos2:            widget methods.    (line 19187)
* parent-w ( -- OPTR ) minos2:           widget methods.    (line 19088)
* parse ( XCHAR "CCC<XCHAR>" -- C-ADDR U ) core-ext,xchar-ext: The Input Stream.
                                                            (line  9261)
* parse-name ( "NAME" -- C-ADDR U ) core-ext: The Input Stream.
                                                            (line  9271)
* parse-word ( -- C-ADDR U ) gforth-obsolete: The Input Stream.
                                                            (line  9274)
* pass ( X1 .. XN N TASK -- ) gforth-experimental: Basic multi-tasking.
                                                            (line 14681)
* path+ ( PATH-ADDR "DIR" -- ) gforth-0.4: General Search Paths.
                                                            (line 10173)
* path= ( PATH-ADDR "DIR1|DIR2|DIR3" -- ) gforth-0.4: General Search Paths.
                                                            (line 10176)
* pause ( -- ) gforth-experimental:      Basic multi-tasking.
                                                            (line 14722)
* perform ( A-ADDR -- ) gforth-0.2:      Execution token.   (line  8173)
* pi ( -- R ) gforth-0.2:                Floating Point.    (line  4439)
* pick ( S:... U -- S:... W ) core-ext:  Data stack.        (line  4536)
* postpone ( "NAME" -- ) core:           Macros.            (line  8441)
* postpone, ( W XT -- ) gforth-0.2:      Compilation token. (line  8319)
* pow2? ( U -- F ) gforth-1.0:           Bitwise operations.
                                                            (line  4185)
* precision ( -- U ) floating-ext:       Floating-point output.
                                                            (line 10640)
* prepend-where ( -- ) gforth-1.0:       Locating uses of a word.
                                                            (line 14088)
* preserve ( "NAME" -- ) gforth-1.0:     Deferred Words.    (line  7882)
* previous ( -- ) search-ext:            Word Lists.        (line  9397)
* print ( OBJECT -- ) objects:           Objects Glossary.  (line 13222)
* printdebugdata ( -- ) gforth-0.2:      Debugging.         (line 14350)
* process-option ( ADDR U -- TRUE / ADDR U FALSE ) gforth-0.7: Modifying the Startup Sequence.
                                                            (line 18353)
* protected ( -- ) objects:              Objects Glossary.  (line 13226)
* ptr ( -- ) oof:                        Class Declaration. (line 13446)
* public ( -- ) objects:                 Objects Glossary.  (line 13229)
* query ( -- ) core-ext-obsolescent:     Input Sources.     (line  8830)
* quit ( ?? -- ?? ) core:                Miscellaneous Words.
                                                            (line 16591)
* r/o ( -- FAM ) file:                   General files.     (line  9897)
* r/w ( -- FAM ) file:                   General files.     (line  9899)
* r> ( R:W -- W ) core:                  Return stack.      (line  4601)
* r@ ( -- W ; R: W -- W ) core:          Return stack.      (line  4603)
* raise ( -- R ) minos2:                 widget methods.    (line 19121)
* rdrop ( R:W -- ) gforth-0.2:           Return stack.      (line  4605)
* re-color ( RGBA "NAME" -- ) minos2:    widget methods.    (line 19236)
* re-emoji-color ( RGBATEXT RGBAEMOJI "NAME" -- ) minos2: widget methods.
                                                            (line 19244)
* re-fade-color ( RGBA1 RGBA2 "NAME" -- ) minos2: widget methods.
                                                            (line 19248)
* re-text-color ( RGBA "NAME" -- ) minos2: widget methods.  (line 19240)
* re-text-emoji-fade-color ( RGBATEXT1 ~2 RGBAEMOJI1 ~2 "NAME" -- ) minos2: widget methods.
                                                            (line 19252)
* read-csv ( ADDR U XT -- ) gforth-experimental: CSV Reader.
                                                            (line 11388)
* read-dir ( C-ADDR U1 WDIRID -- U2 FLAG WIOR ) gforth-0.5: Directories.
                                                            (line 10053)
* read-file ( C-ADDR U1 WFILEID -- U2 WIOR ) file: General files.
                                                            (line  9924)
* read-line ( C_ADDR U1 WFILEID -- U2 FLAG WIOR ) file: General files.
                                                            (line  9930)
* rec-body ( ADDR U -- XT TRANSLATE-TICK | TRANSLATE-NULL ) gforth-experimental: Dealing with existing Recognizers.
                                                            (line  9159)
* rec-dtick ( ADDR U -- NT RECTYPE-NUM | RECTYPE-NULL ) gforth-experimental: Dealing with existing Recognizers.
                                                            (line  9155)
* rec-float ( ADDR U -- R TRANSLATE-FLOAT | NOTFOUND ) gforth-experimental: Dealing with existing Recognizers.
                                                            (line  9139)
* rec-moof2 ( ADDR U -- XT TRANSLATE-MOOF2 | NOTFOUND ) mini-oof2: Mini-OOF2.
                                                            (line 13703)
* rec-nt ( ADDR U -- NT TRANSLATE-NT | NOTFOUND ) gforth-experimental: Dealing with existing Recognizers.
                                                            (line  9133)
* rec-num ( ADDR U -- N/D TABLE | NOTFOUND ) gforth-experimental: Dealing with existing Recognizers.
                                                            (line  9136)
* rec-string ( ADDR U -- ADDR U' R:STRING | RECTYPE-NULL ) gforth-experimental: Dealing with existing Recognizers.
                                                            (line  9142)
* rec-tick ( ADDR U -- XT RECTYPE-NUM | RECTYPE-NULL ) gforth-experimental: Dealing with existing Recognizers.
                                                            (line  9151)
* rec-to ( ADDR U -- XT N R:TO | RECTYPE-NULL ) gforth-experimental: Dealing with existing Recognizers.
                                                            (line  9146)
* recognize ( ADDR U REC-ADDR -- ... RECTYPE ) gforth-experimental: Dealing with existing Recognizers.
                                                            (line  9169)
* recognizer-sequence: ( XT1 .. XTN N "NAME" -- ) gforth-experimental: Dealing with existing Recognizers.
                                                            (line  9172)
* recurse ( ... -- ... ) core:           Calls and returns. (line  6376)
* recursive ( COMPILATION -- ; RUN-TIME -- ) gforth-0.2: Calls and returns.
                                                            (line  6372)
* refill ( -- FLAG ) core-ext,block-ext,file-ext: The Input Stream.
                                                            (line  9290)
* rename-file ( C-ADDR1 U1 C-ADDR2 U2 -- WIOR ) file-ext: General files.
                                                            (line  9921)
* REPEAT ( COMPILATION ORIG DEST -- ; RUN-TIME -- ) core: Arbitrary control structures.
                                                            (line  6278)
* replace-word ( XT1 XT2 -- ) gforth-1.0: Debugging.        (line 14383)
* replaces ( ADDR1 LEN1 ADDR2 LEN2 -- ) string-ext: Substitute.
                                                            (line 11355)
* reposition-file ( UD WFILEID -- WIOR ) file: General files.
                                                            (line  9970)
* represent ( R C-ADDR U -- N F1 F2 ) floating: Floating-point output.
                                                            (line 10702)
* require ( ... "FILE" -- ... ) file-ext: Forth source files.
                                                            (line  9864)
* required ( I*X ADDR U -- I*X ) file-ext: Forth source files.
                                                            (line  9858)
* resize ( A_ADDR1 U -- A_ADDR2 WIOR ) memory: Heap Allocation.
                                                            (line  4821)
* resize-file ( UD WFILEID -- WIOR ) file: General files.   (line  9974)
* resized ( -- ) minos2:                 widget methods.    (line 19190)
* restart ( TASK -- ) gforth-experimental: Basic multi-tasking.
                                                            (line 14717)
* restore ( COMPILATION ORIG1 -- ; RUN-TIME -- ) gforth-0.7: Exception Handling.
                                                            (line  6622)
* restore-input ( X1 .. XN N -- FLAG ) core-ext: Input Sources.
                                                            (line  8815)
* restrict ( -- ) gforth-0.2:            Interpretation and Compilation Semantics.
                                                            (line  7995)
* return-stack-cells ( -- N ) environment: Environmental Queries.
                                                            (line  9650)
* reveal ( -- ) gforth-0.2:              Creating from a prototype.
                                                            (line  7708)
* rol ( U1 U -- U2 ) gforth-1.0:         Bitwise operations.
                                                            (line  4214)
* roll ( X0 X1 .. XN N -- X1 .. XN X0 ) core-ext: Data stack.
                                                            (line  4547)
* Root ( -- ) gforth-0.2:                Word Lists.        (line  9464)
* ror ( U1 U -- U2 ) gforth-1.0:         Bitwise operations.
                                                            (line  4217)
* rot ( W1 W2 W3 -- W2 W3 W1 ) core:     Data stack.        (line  4539)
* rp! ( A-ADDR -- ) gforth-0.2:          Stack pointer manipulation.
                                                            (line  4647)
* rp0 ( -- A-ADDR ) gforth-0.4:          Stack pointer manipulation.
                                                            (line  4642)
* rp@ ( -- A-ADDR ) gforth-0.2:          Stack pointer manipulation.
                                                            (line  4645)
* rshift ( U1 U -- U2 ) core:            Bitwise operations.
                                                            (line  4145)
* S" ( COMPILATION 'CCC"' -- ; RUN-TIME -- C-ADDR U ) core,file: String and character literals.
                                                            (line  5327)
* s+ ( C-ADDR1 U1 C-ADDR2 U2 -- C-ADDR U ) gforth-0.7: String words.
                                                            (line  5472)
* s// ( ADDR U -- PTR ) regexp-replace:  Regular Expressions.
                                                            (line 13956)
* s>> ( ADDR -- ADDR ) regexp-replace:   Regular Expressions.
                                                            (line 13943)
* s>d ( N -- D ) core:                   Double precision.  (line  3843)
* s>f ( N -- R ) floating-ext:           Floating Point.    (line  4326)
* s>number? ( ADDR U -- D F ) gforth-0.5: Line input and conversion.
                                                            (line 11080)
* s>unumber? ( C-ADDR U -- UD FLAG ) gforth-0.5: Line input and conversion.
                                                            (line 11083)
* safe/string ( C-ADDR1 U1 N -- C-ADDR2 U2 ) gforth-1.0: String words.
                                                            (line  5442)
* save-buffer ( BUFFER -- ) gforth-0.2:  Blocks.            (line 10364)
* save-buffers ( -- ) block:             Blocks.            (line 10360)
* save-cov ( -- ) gforth-experimental:   Code Coverage.     (line 14605)
* save-input ( -- X1 .. XN N ) core-ext: Input Sources.     (line  8810)
* save-mem ( ADDR1 U -- ADDR2 U ) gforth-0.2: Heap Allocation.
                                                            (line  4831)
* savesystem ( "IMAGE" -- ) gforth-0.2:  Non-Relocatable Image Files.
                                                            (line 18103)
* scan ( C-ADDR1 U1 C -- C-ADDR2 U2 ) gforth-0.2: String words.
                                                            (line  5422)
* scan-back ( C-ADDR U1 C -- C-ADDR U2 ) gforth-0.7: String words.
                                                            (line  5427)
* scope ( COMPILATION -- SCOPE ; RUN-TIME -- ) gforth-0.2: Where are locals visible by name?.
                                                            (line 11674)
* scr ( -- A-ADDR ) block-ext:           Blocks.            (line 10327)
* scrolled ( AXIS DIR -- ) minos2:       actor methods.     (line 19040)
* seal ( -- ) gforth-0.2:                Word Lists.        (line  9474)
* search ( C-ADDR1 U1 C-ADDR2 U2 -- C-ADDR3 U3 FLAG ) string: String words.
                                                            (line  5416)
* search-wordlist ( C-ADDR COUNT WID -- 0 | XT +-1 ) search: Word Lists.
                                                            (line  9440)
* see ( "<SPACES>NAME" -- ) tools:       Examining compiled code.
                                                            (line 14115)
* see-code ( "NAME" -- ) gforth-0.7:     Examining compiled code.
                                                            (line 14134)
* see-code-range ( ADDR1 ADDR2 -- ) gforth-0.7: Examining compiled code.
                                                            (line 14148)
* select ( U1 U2 F -- U ) gforth-1.0:    Boolean Flags.     (line  3774)
* selector ( "NAME" -- ) objects:        Objects Glossary.  (line 13233)
* semaphore ( "NAME" -- ) gforth-experimental: Semaphores.  (line 14784)
* send-event ( XT TASK -- ) gforth-experimental: Message queues.
                                                            (line 14844)
* set ( SOMETHING -- ) minos2:           actor methods.     (line 19079)
* set->comp ( XT -- ) gforth-1.0:        Header methods.    (line 16355)
* set->int ( XT -- ) gforth-1.0:         Header methods.    (line 16343)
* set-current ( WID -- ) search:         Word Lists.        (line  9365)
* set-dir ( C-ADDR U -- WIOR ) gforth-0.7: Directories.     (line 10076)
* set-does> ( XT -- ) gforth-1.0:        CREATE..DOES> details.
                                                            (line  7395)
* set-execute ( CA -- ) gforth-1.0:      Header methods.    (line 16232)
* set-forth-recognize ( XT -- ) recognizer: Dealing with existing Recognizers.
                                                            (line  9183)
* set-name>link ( XT -- ) gforth-1.0:    Header methods.    (line 16374)
* set-name>string ( XT -- ) gforth-1.0:  Header methods.    (line 16370)
* set-optimizer ( XT -- ) gforth-1.0:    User-defined compile-comma.
                                                            (line  7574)
* set-order ( WIDN .. WID1 N -- ) search: Word Lists.       (line  9374)
* set-precision ( U -- ) floating-ext:   Floating-point output.
                                                            (line 10644)
* set-recognizers ( XT1 .. XTN N -- ) gforth-experimental: Dealing with existing Recognizers.
                                                            (line  9166)
* set-to ( TO-XT -- ) gforth-1.0:        User-defined TO and DEFER@.
                                                            (line  7533)
* sf! ( R SF-ADDR -- ) floating-ext:     Memory Access.     (line  4906)
* sf@ ( SF-ADDR -- R ) floating-ext:     Memory Access.     (line  4902)
* sfalign ( -- ) floating-ext:           Dictionary allocation.
                                                            (line  4780)
* sfaligned ( C-ADDR -- SF-ADDR ) floating-ext: Address arithmetic.
                                                            (line  5124)
* sffield: ( U1 "NAME" -- U2 ) floating-ext: Forth200x Structures.
                                                            (line 12507)
* sfloat% ( -- ALIGN SIZE ) gforth-0.4:  Structure Glossary.
                                                            (line 12437)
* sfloat+ ( SF-ADDR1 -- SF-ADDR2 ) floating-ext: Address arithmetic.
                                                            (line  5119)
* sfloat/ ( N1 -- N2 ) gforth-1.0:       Address arithmetic.
                                                            (line  5122)
* sfloats ( N1 -- N2 ) floating-ext:     Address arithmetic.
                                                            (line  5115)
* sh ( "..." -- ) gforth-0.2:            Passing Commands to the OS.
                                                            (line 16529)
* sh-get ( C-ADDR U -- C-ADDR2 U2 ) gforth-1.0: Passing Commands to the OS.
                                                            (line 16541)
* shift-args ( -- ) gforth-0.7:          OS command line arguments.
                                                            (line 11439)
* short-where ( -- ) gforth-1.0:         Locating uses of a word.
                                                            (line 14081)
* show ( -- ) minos2:                    actor methods.     (line 19070)
* show-you ( -- ) minos2:                actor methods.     (line 19082)
* sign ( N -- ) core:                    Formatted numeric output.
                                                            (line 10525)
* simple-fkey-string ( U1 -- C-ADDR U ) gforth-1.0: Single-key input.
                                                            (line 11054)
* simple-see ( "NAME" -- ) gforth-0.6:   Examining compiled code.
                                                            (line 14124)
* simple-see-range ( ADDR1 ADDR2 -- ) gforth-0.6: Examining compiled code.
                                                            (line 14131)
* skip ( C-ADDR1 U1 C -- C-ADDR2 U2 ) gforth-0.2: String words.
                                                            (line  5429)
* SLiteral ( COMPILATION C-ADDR1 U ; RUN-TIME -- C-ADDR2 U ) string: Literals.
                                                            (line  8403)
* slurp-fid ( FID -- ADDR U ) gforth-0.6: General files.    (line  9979)
* slurp-file ( C-ADDR1 U1 -- C-ADDR2 U2 ) gforth-0.6: General files.
                                                            (line  9976)
* sm/rem ( D1 N1 -- N2 N3 ) core:        Integer division.  (line  3947)
* source ( -- ADDR U ) core:             The Text Interpreter.
                                                            (line  8756)
* source-id ( -- 0 | -1 | FILEID ) core-ext,file: Input Sources.
                                                            (line  8801)
* sourcefilename ( -- C-ADDR U ) gforth-0.2: Forth source files.
                                                            (line  9876)
* sourceline# ( -- U ) gforth-0.2:       Forth source files.
                                                            (line  9883)
* sp! ( A-ADDR -- S:... ) gforth-0.2:    Stack pointer manipulation.
                                                            (line  4633)
* sp0 ( -- A-ADDR ) gforth-0.4:          Stack pointer manipulation.
                                                            (line  4628)
* sp@ ( S:... -- A-ADDR ) gforth-0.2:    Stack pointer manipulation.
                                                            (line  4631)
* space ( -- ) core:                     Miscellaneous output.
                                                            (line 10716)
* spaces ( U -- ) core:                  Miscellaneous output.
                                                            (line 10719)
* span ( -- C-ADDR ) core-ext-obsolescent: Line input and conversion.
                                                            (line 11128)
* spawn ( XT -- ) cilk:                  Cilk.              (line 14895)
* spawn1 ( X XT -- ) cilk:               Cilk.              (line 14901)
* spawn2 ( X1 X2 XT -- ) cilk:           Cilk.              (line 14904)
* split ( FIRSTFLAG RSTART1 RX -- O RSTART2 ) minos2: widget methods.
                                                            (line 19145)
* stack-cells ( -- N ) environment:      Environmental Queries.
                                                            (line  9653)
* stacksize ( -- U ) gforth-experimental: Basic multi-tasking.
                                                            (line 14655)
* stacksize4 ( -- U-DATA U-RETURN U-FP U-LOCALS ) gforth-experimental: Basic multi-tasking.
                                                            (line 14658)
* staged/-divisor ( ADDR1 -- ADDR2 ) gforth-1.0: Two-stage integer division.
                                                            (line  4098)
* staged/-size ( -- U ) gforth-1.0:      Two-stage integer division.
                                                            (line  4056)
* static ( -- ) oof:                     Class Declaration. (line 13467)
* status-color ( -- ) gforth-1.0:        Terminal output.   (line 10853)
* stderr ( -- WFILEID ) gforth-0.2:      General files.     (line  9988)
* stdin ( -- WFILEID ) gforth-0.4:       General files.     (line  9982)
* stdout ( -- WFILEID ) gforth-0.2:      General files.     (line  9985)
* stop ( -- ) gforth-experimental:       Basic multi-tasking.
                                                            (line 14708)
* stop-ns ( TIMEOUT -- ) gforth-experimental: Basic multi-tasking.
                                                            (line 14711)
* str< ( C-ADDR1 U1 C-ADDR2 U2 -- F ) gforth-0.6: String words.
                                                            (line  5408)
* str= ( C-ADDR1 U1 C-ADDR2 U2 -- F ) gforth-0.6: String words.
                                                            (line  5406)
* str=? ( ADDR1 ADDR U -- ADDR2 ) regexp-pattern: Regular Expressions.
                                                            (line 13880)
* string, ( C-ADDR U -- ) gforth-0.2:    Counted string words.
                                                            (line  5678)
* string-parse ( C-ADDR1 U1 "CCC<STRING>" -- C-ADDR2 U2 ) gforth-1.0: The Input Stream.
                                                            (line  9266)
* string-prefix? ( C-ADDR1 U1 C-ADDR2 U2 -- F ) gforth-0.6: String words.
                                                            (line  5410)
* string-suffix? ( C-ADDR1 U1 C-ADDR2 U2 -- F ) gforth-1.0: String words.
                                                            (line  5413)
* struct ( -- ALIGN SIZE ) gforth-0.2:   Structure Glossary.
                                                            (line 12442)
* sub-list? ( LIST1 LIST2 -- F ) gforth-internal: Locals implementation.
                                                            (line 12014)
* substitute ( ADDR1 LEN1 ADDR2 LEN2 -- ADDR2 LEN3 N/IOR ) string-ext: Substitute.
                                                            (line 11367)
* success-color ( -- ) gforth-1.0:       Terminal output.   (line 10847)
* swap ( W1 W2 -- W2 W1 ) core:          Data stack.        (line  4534)
* Synonym ( "NAME" "OLDNAME" -- ) tools-ext: Aliases.       (line  7916)
* system ( C-ADDR U -- ) gforth-0.2:     Passing Commands to the OS.
                                                            (line 16533)
* s\" ( COMPILATION 'CCC"' -- ; RUN-TIME -- C-ADDR U ) core-ext,file-ext: String and character literals.
                                                            (line  5309)
* table ( -- WID ) gforth-0.2:           Word Lists.        (line  9385)
* task ( USTACKSIZE "NAME" -- ) gforth-experimental: Basic multi-tasking.
                                                            (line 14643)
* text-color: ( RGBA "NAME" -- ) minos2: widget methods.    (line 19216)
* text-emoji-color: ( RGBATEXT RGBAEMOJI "NAME" -- ) minos2: widget methods.
                                                            (line 19220)
* text-emoji-fade-color: ( RGBATEXT1 ~2 RGBAEMOJI1 ~2 "NAME" -- ) minos2: widget methods.
                                                            (line 19230)
* THEN ( COMPILATION ORIG -- ; RUN-TIME -- ) core: Arbitrary control structures.
                                                            (line  6235)
* third ( W1 W2 W3 -- W1 W2 W3 W1 ) gforth-1.0: Data stack. (line  4528)
* this ( -- OBJECT ) objects:            Objects Glossary.  (line 13238)
* threading-method ( -- N ) gforth-0.2:  Threading Words.   (line 16444)
* throw ( Y1 .. YM NERROR -- Y1 .. YM / Z1 .. ZN ERROR ) exception: Exception Handling.
                                                            (line  6425)
* thru ( I*X N1 N2 -- J*X ) block-ext:   Blocks.            (line 10372)
* tib ( -- ADDR ) core-ext-obsolescent:  The Text Interpreter.
                                                            (line  8759)
* time&date ( -- NSEC NMIN NHOUR NDAY NMONTH NYEAR ) facility-ext: Keeping track of Time.
                                                            (line 16562)
* TO ( VALUE "NAME" -- ) core-ext:       Values.            (line  6893)
* to-method: ( XT TABLE "NAME" -- ) gforth-experimental: User-defined TO and DEFER@.
                                                            (line  7529)
* to-table: ( "NAME" "XT1" .. "XTN" -- ) gforth-experimental: User-defined TO and DEFER@.
                                                            (line  7525)
* to-this ( OBJECT -- ) objects:         Objects Glossary.  (line 13247)
* touchdown ( $RXY*N BMASK -- ) minos2:  actor methods.     (line 19043)
* touchup ( $RXY*N BMASK -- ) minos2:    actor methods.     (line 19046)
* toupper ( C1 -- C2 ) gforth-0.2:       Characters.        (line  5274)
* translate-dnum ( DX -- | DX ) gforth-experimental: Dealing with existing Recognizers.
                                                            (line  9196)
* translate-method: ( "NAME" -- ) gforth-experimental: Dealing with existing Recognizers.
                                                            (line  9215)
* translate-nt ( I*X NT -- J*X ) gforth-experimental: Dealing with existing Recognizers.
                                                            (line  9190)
* translate-num ( X -- | X ) gforth-experimental: Dealing with existing Recognizers.
                                                            (line  9193)
* translate-state ( XT -- ) gforth-experimental: Dealing with existing Recognizers.
                                                            (line  9220)
* translate: ( INT-XT COMP-XT POST-XT "NAME" -- ) gforth-experimental: Dealing with existing Recognizers.
                                                            (line  9186)
* traverse-wordlist ( ... XT WID -- ... ) tools-ext: Name token.
                                                            (line  8233)
* true ( -- F ) core-ext:                Boolean Flags.     (line  3762)
* try ( COMPILATION -- ORIG ; RUN-TIME -- R:SYS1 ) gforth-0.5: Exception Handling.
                                                            (line  6544)
* try-recognize ( ADDR U XT -- RESULTS | FALSE ) gforth-experimental: Dealing with existing Recognizers.
                                                            (line  9199)
* tt ( U -- ) gforth-1.0:                Locating exception source.
                                                            (line 14101)
* tuck ( W1 W2 -- W2 W1 W2 ) core-ext:   Data stack.        (line  4532)
* type ( C-ADDR U -- ) core:             Displaying characters and strings.
                                                            (line 10782)
* typewhite ( ADDR N -- ) gforth-0.2:    Displaying characters and strings.
                                                            (line 10793)
* u*/ ( U1 U2 U3 -- U4 ) gforth-1.0:     Integer division.  (line  3965)
* u*/mod ( U1 U2 U3 -- U4 U5 ) gforth-1.0: Integer division.
                                                            (line  3980)
* U+DO ( COMPILATION -- DO-SYS ; RUN-TIME U1 U2 -- | LOOP-SYS ) gforth-0.2: Counted Loops.
                                                            (line  5990)
* U-DO ( COMPILATION -- DO-SYS ; RUN-TIME U1 U2 -- | LOOP-SYS ) gforth-0.2: Counted Loops.
                                                            (line  6011)
* u-[do ( COMPILATION -- DO-SYS ; RUN-TIME U1 U2 -- | LOOP-SYS ) gforth-experimental: Counted Loops.
                                                            (line  6003)
* u. ( U -- ) core:                      Simple numeric output.
                                                            (line 10423)
* u.r ( U N -- ) core-ext:               Simple numeric output.
                                                            (line 10434)
* u/ ( U1 U2 -- U ) gforth-1.0:          Integer division.  (line  3916)
* u/-stage1m ( U ADDR-RECI -- ) gforth-1.0: Two-stage integer division.
                                                            (line  4076)
* u/-stage2m ( U1 A-RECI -- UQUOTIENT ) gforth-1.0: Two-stage integer division.
                                                            (line  4080)
* u/mod ( U1 U2 -- U3 U4 ) gforth-1.0:   Integer division.  (line  3936)
* u/mod-stage2m ( U1 A-RECI -- UMODULUS UQUOTIENT ) gforth-1.0: Two-stage integer division.
                                                            (line  4088)
* u< ( U1 U2 -- F ) core:                Numeric comparison.
                                                            (line  4256)
* u<= ( U1 U2 -- F ) gforth-0.2:         Numeric comparison.
                                                            (line  4258)
* u> ( U1 U2 -- F ) core-ext:            Numeric comparison.
                                                            (line  4260)
* u>= ( U1 U2 -- F ) gforth-0.2:         Numeric comparison.
                                                            (line  4262)
* uallot ( N1 -- N2 ) gforth-0.3:        Task-local data.   (line 14747)
* ud. ( UD -- ) gforth-0.2:              Simple numeric output.
                                                            (line 10445)
* ud.r ( UD N -- ) gforth-0.2:           Simple numeric output.
                                                            (line 10454)
* ud/mod ( UD1 U2 -- UREM UDQUOT ) gforth-0.2: Integer division.
                                                            (line  3986)
* UDefer ( "NAME" -- ) gforth-1.0:       Task-local data.   (line 14755)
* ukeyed ( ADDR U -- ) minos2:           actor methods.     (line 19049)
* um* ( U1 U2 -- UD ) core:              Mixed precision.   (line  3866)
* um/mod ( UD U1 -- U2 U3 ) core:        Integer division.  (line  3950)
* umax ( U1 U2 -- U ) gforth-1.0:        Single precision.  (line  3823)
* umin ( U1 U2 -- U ) gforth-0.5:        Single precision.  (line  3821)
* umod ( U1 U2 -- U ) gforth-1.0:        Integer division.  (line  3925)
* umod-stage2m ( U1 A-RECI -- UMODULUS ) gforth-1.0: Two-stage integer division.
                                                            (line  4084)
* uncolored-mode ( -- ) gforth-1.0:      Terminal output.   (line 10868)
* under+ ( N1 N2 N3 -- N N2 ) gforth-0.3: Single precision. (line  3804)
* unescape ( ADDR1 U1 DEST -- DEST U2 ) string-ext: Substitute.
                                                            (line 11372)
* unlock ( SEMAPHORE -- ) gforth-experimental: Semaphores.  (line 14791)
* unloop ( R:W1 R:W2 -- ) core:          Counted Loops.     (line  6064)
* UNREACHABLE ( -- ) gforth-0.2:         Where are locals visible by name?.
                                                            (line 11712)
* UNTIL ( COMPILATION DEST -- ; RUN-TIME F -- ) core: Arbitrary control structures.
                                                            (line  6243)
* unused ( -- U ) core-ext:              Dictionary allocation.
                                                            (line  4717)
* unused-words ( -- ) gforth-1.0:        Locating uses of a word.
                                                            (line 14095)
* up@ ( -- A-ADDR ) new:                 Task-local data.   (line 14761)
* update ( -- ) block:                   Blocks.            (line 10353)
* updated? ( N -- F ) gforth-0.2:        Blocks.            (line 10356)
* use ( "FILE" -- ) gforth-0.2:          Blocks.            (line 10307)
* User ( "NAME" -- ) gforth-0.2:         Task-local data.   (line 14738)
* user' ( "NAME" -- U ) gforth-experimental: Task-local data.
                                                            (line 14765)
* utime ( -- DTIME ) gforth-0.5:         Keeping track of Time.
                                                            (line 16571)
* UValue ( "NAME" -- ) gforth-1.0:       Task-local data.   (line 14751)
* v* ( F-ADDR1 NSTRIDE1 F-ADDR2 NSTRIDE2 UCOUNT -- R ) gforth-0.5: Floating Point.
                                                            (line  4397)
* Value ( W "NAME" -- ) core-ext:        Values.            (line  6877)
* var ( M V SIZE "NAME" -- M V' ) mini-oof: Basic Mini-OOF Usage.
                                                            (line 13503)
* var ( SIZE -- ) oof:                   Class Declaration. (line 13441)
* Variable ( "NAME" -- ) core:           Variables.         (line  6771)
* Varue ( W "NAME" -- ) gforth-1.0:      Varues.            (line  6907)
* vglue ( -- RTYP RSUB RADD ) minos2:    widget methods.    (line 19157)
* vglue@ ( -- RTYP RSUB RADD ) minos2:   widget methods.    (line 19166)
* vlist ( -- ) gforth-0.2:               Word Lists.        (line  9452)
* Vocabulary ( "NAME" -- ) gforth-0.2:   Word Lists.        (line  9469)
* vocs ( -- ) gforth-0.2:                Word Lists.        (line  9478)
* vp-bottom ( O:VP -- ) minos2:          widget methods.    (line 19264)
* vp-left ( O:VP -- ) minos2:            widget methods.    (line 19267)
* vp-needed ( XT -- ) minos2:            widget methods.    (line 19276)
* vp-reslide ( O:VP -- ) minos2:         widget methods.    (line 19273)
* vp-right ( O:VP -- ) minos2:           widget methods.    (line 19270)
* vp-top ( O:VP -- ) minos2:             widget methods.    (line 19261)
* w ( -- R ) minos2:                     widget methods.    (line 19103)
* w! ( W C-ADDR -- ) gforth-0.7:         Special Memory Accesses.
                                                            (line  4954)
* w, ( W -- ) gforth-1.0:                Dictionary allocation.
                                                            (line  4745)
* w-color ( -- R ) minos2:               widget methods.    (line 19136)
* w/o ( -- FAM ) file:                   General files.     (line  9901)
* W: ( COMPILATION "NAME" -- A-ADDR XT; RUN-TIME X -- ) gforth-0.2: Locals definition words.
                                                            (line 11619)
* w>s ( X -- N ) gforth-1.0:             Special Memory Accesses.
                                                            (line  5018)
* w@ ( C-ADDR -- U ) gforth-0.5:         Special Memory Accesses.
                                                            (line  4951)
* WA: ( COMPILATION "NAME" -- A-ADDR XT; RUN-TIME X -- ) gforth-1.0: Locals definition words.
                                                            (line 11622)
* walign ( -- ) gforth-1.0:              Address arithmetic.
                                                            (line  5159)
* waligned ( ADDR -- ADDR' ) gforth-1.0: Address arithmetic.
                                                            (line  5156)
* WARNING" ( COMPILATION 'CCC"' -- ; RUN-TIME F -- ) gforth-1.0: Exception Handling.
                                                            (line  6671)
* warning-color ( -- ) gforth-1.0:       Terminal output.   (line 10841)
* warnings ( -- ADDR ) gforth-0.2:       Exception Handling.
                                                            (line  6674)
* wbe ( U1 -- U2 ) gforth-1.0:           Special Memory Accesses.
                                                            (line  4980)
* wfield: ( U1 "NAME" -- U2 ) gforth-1.0: Forth200x Structures.
                                                            (line 12513)
* where ( "NAME" -- ) gforth-1.0:        Locating uses of a word.
                                                            (line 14047)
* whereg ( "NAME" -- ) gforth-1.0:       Locating uses of a word.
                                                            (line 14076)
* WHILE ( COMPILATION DEST -- ORIG DEST ; RUN-TIME F -- ) core: Arbitrary control structures.
                                                            (line  6273)
* widget ( -- CLASS ) minos2:            MINOS2 object framework.
                                                            (line 19022)
* within ( U1 U2 U3 -- F ) core-ext:     Numeric comparison.
                                                            (line  4264)
* wle ( U1 -- U2 ) gforth-1.0:           Special Memory Accesses.
                                                            (line  4984)
* word ( CHAR "<CHARS>CCC<CHAR>-- C-ADDR ) core: The Input Stream.
                                                            (line  9281)
* wordlist ( -- WID ) search:            Word Lists.        (line  9382)
* wordlist-words ( WID -- ) gforth-0.6:  Word Lists.        (line  9455)
* wordlists ( -- N ) environment:        Environmental Queries.
                                                            (line  9663)
* words ( -- ) tools:                    Word Lists.        (line  9448)
* wrap-xt ( XT1 XT2 XT: XT3 -- ... ) gforth-1.0: Deferred Words.
                                                            (line  7879)
* write-file ( C-ADDR U1 WFILEID -- WIOR ) file: General files.
                                                            (line  9958)
* write-line ( C-ADDR U WFILEID -- IOR ) file: General files.
                                                            (line  9960)
* wrol ( U1 U -- U2 ) gforth-1.0:        Bitwise operations.
                                                            (line  4198)
* wror ( U1 U -- U2 ) gforth-1.0:        Bitwise operations.
                                                            (line  4202)
* WTF?? ( -- ) gforth-1.0:               Debugging.         (line 14377)
* ww ( U -- ) gforth-1.0:                Locating uses of a word.
                                                            (line 14053)
* W^ ( COMPILATION "NAME" -- A-ADDR XT; RUN-TIME X -- ) gforth-0.2: Locals definition words.
                                                            (line 11625)
* x ( -- R ) minos2:                     widget methods.    (line 19097)
* x! ( W C-ADDR -- ) gforth-1.0:         Special Memory Accesses.
                                                            (line  4966)
* x, ( X -- ) gforth-1.0:                Dictionary allocation.
                                                            (line  4749)
* x-size ( XC-ADDR U1 -- U2 ) xchar:     Xchars and Unicode.
                                                            (line 11202)
* x-width ( XC-ADDR U -- N ) xchar-ext:  Xchars and Unicode.
                                                            (line 11256)
* x>s ( X -- N ) gforth-1.0:             Special Memory Accesses.
                                                            (line  5024)
* x@ ( C-ADDR -- U ) gforth-1.0:         Special Memory Accesses.
                                                            (line  4963)
* xalign ( -- ) gforth-1.0:              Address arithmetic.
                                                            (line  5171)
* xaligned ( ADDR -- ADDR' ) gforth-1.0: Address arithmetic.
                                                            (line  5168)
* xbe ( U1 -- U2 ) gforth-1.0:           Special Memory Accesses.
                                                            (line  4996)
* xc!+ ( XC XC-ADDR1 -- XC-ADDR2 ) xchar: Xchars and Unicode.
                                                            (line 11225)
* xc!+? ( XC XC-ADDR1 U1 -- XC-ADDR2 U2 F ) xchar: Xchars and Unicode.
                                                            (line 11217)
* xc, ( XCHAR -- ) xchar:                Xchars and Unicode.
                                                            (line 11273)
* xc-size ( XC -- U ) xchar:             Xchars and Unicode.
                                                            (line 11199)
* xc-width ( XC -- N ) xchar-ext:        Xchars and Unicode.
                                                            (line 11266)
* xc@ ( XC-ADDR -- XC ) xchar-ext:       Xchars and Unicode.
                                                            (line 11206)
* xc@+ ( XC-ADDR1 -- XC-ADDR2 XC ) xchar: Xchars and Unicode.
                                                            (line 11209)
* xc@+? ( XC-ADDR1 U1 -- XC-ADDR2 U2 XC ) gforth-experimental: Xchars and Unicode.
                                                            (line 11213)
* xchar+ ( XC-ADDR1 -- XC-ADDR2 ) xchar: Xchars and Unicode.
                                                            (line 11232)
* xchar- ( XC-ADDR1 -- XC-ADDR2 ) xchar-ext: Xchars and Unicode.
                                                            (line 11236)
* XCHAR-ENCODING ( -- ADDR U ) environment: Environmental Queries.
                                                            (line  9670)
* XCHAR-MAXMEM ( -- U ) environment:     Environmental Queries.
                                                            (line  9680)
* xd! ( UD C-ADDR -- ) gforth-1.0:       Special Memory Accesses.
                                                            (line  4972)
* xd, ( XD -- ) gforth-1.0:              Dictionary allocation.
                                                            (line  4751)
* xd>s ( XD -- D ) gforth-1.0:           Special Memory Accesses.
                                                            (line  5027)
* xd@ ( C-ADDR -- UD ) gforth-1.0:       Special Memory Accesses.
                                                            (line  4969)
* xdbe ( UD1 -- UD2 ) gforth-1.0:        Special Memory Accesses.
                                                            (line  5004)
* xdle ( UD1 -- UD2 ) gforth-1.0:        Special Memory Accesses.
                                                            (line  5008)
* xemit ( XC -- ) xchar:                 Displaying characters and strings.
                                                            (line 10786)
* xfield: ( U1 "NAME" -- U2 ) gforth-1.0: Forth200x Structures.
                                                            (line 12519)
* xhold ( XC -- ) xchar-ext:             Xchars and Unicode.
                                                            (line 11269)
* xkey ( -- XC ) xchar:                  Xchars and Unicode.
                                                            (line 11262)
* xkey? ( -- FLAG ) xchar:               Single-key input.  (line 10893)
* xle ( U1 -- U2 ) gforth-1.0:           Special Memory Accesses.
                                                            (line  5000)
* xor ( W1 W2 -- W ) core:               Bitwise operations.
                                                            (line  4133)
* xt-new ( ... CLASS XT -- OBJECT ) objects: Objects Glossary.
                                                            (line 13250)
* xt-see ( XT -- ) gforth-0.2:           Examining compiled code.
                                                            (line 14121)
* xt-see-code ( XT -- ) gforth-1.0:      Examining compiled code.
                                                            (line 14145)
* xt-simple-see ( XT -- ) gforth-1.0:    Examining compiled code.
                                                            (line 14128)
* XT: ( COMPILATION "NAME" -- A-ADDR XT; RUN-TIME XT1 -- ) gforth-1.0: Locals definition words.
                                                            (line 11655)
* xt>name ( XT -- NT ) gforth-1.0:       Name token.        (line  8227)
* XTA: ( COMPILATION "NAME" -- A-ADDR XT; RUN-TIME ... -- ... ) gforth-1.0: Locals definition words.
                                                            (line 11658)
* xywh ( -- RX0 RY0 RW RH ) minos2:      widget methods.    (line 19169)
* xywhd ( -- RX RY RW RH RD ) minos2:    widget methods.    (line 19172)
* x\string- ( XC-ADDR U1 -- XC-ADDR U2 ) xchar-ext: Xchars and Unicode.
                                                            (line 11245)
* y ( -- R ) minos2:                     widget methods.    (line 19100)

Concept and Word Index
**********************

Not all entries listed in this index are present verbatim in the text.
This index also duplicates, in abbreviated form, all of the words listed
in the Word Index (only the names are listed for the words here).

* Menu:

* !:                                     Memory Access.     (line  4877)
* !!FIXME!!:                             Debugging.         (line 14380)
* !@:                                    Hardware operations for multi-tasking.
                                                            (line 14814)
* !resize:                               widget methods.    (line 19175)
* !size:                                 widget methods.    (line 19178)
* ", stack item type:                    Notation.          (line  3698)
* #:                                     Formatted numeric output.
                                                            (line 10506)
* #!:                                    Running Image Files.
                                                            (line 18288)
* #-prefix for decimal numbers:          Literals in source code.
                                                            (line  3465)
* #>:                                    Formatted numeric output.
                                                            (line 10529)
* #>>:                                   Formatted numeric output.
                                                            (line 10536)
* #bell:                                 String and character literals.
                                                            (line  5389)
* #bs:                                   String and character literals.
                                                            (line  5385)
* #cr:                                   String and character literals.
                                                            (line  5381)
* #del:                                  String and character literals.
                                                            (line  5387)
* #eof:                                  String and character literals.
                                                            (line  5393)
* #esc:                                  String and character literals.
                                                            (line  5391)
* #ff:                                   String and character literals.
                                                            (line  5383)
* #lf:                                   String and character literals.
                                                            (line  5379)
* #line:                                 Interpreter Directives.
                                                            (line  9000)
* #loc:                                  Debugging.         (line 14398)
* #locals:                               Environmental Queries.
                                                            (line  9660)
* #s:                                    Formatted numeric output.
                                                            (line 10511)
* #tab:                                  String and character literals.
                                                            (line  5377)
* #tib:                                  The Text Interpreter.
                                                            (line  8761)
* $!:                                    $tring words.      (line  5517)
* $!len:                                 $tring words.      (line  5527)
* $+!:                                   $tring words.      (line  5541)
* $+!len:                                $tring words.      (line  5531)
* $+slurp:                               $tring words.      (line  5582)
* $+slurp-file:                          $tring words.      (line  5586)
* $+[]!:                                 $tring words.      (line  5601)
* $-prefix for hexadecimal numbers:      Literals in source code.
                                                            (line  3465)
* $.:                                    $tring words.      (line  5572)
* $?:                                    Passing Commands to the OS.
                                                            (line 16545)
* $@:                                    $tring words.      (line  5521)
* $@len:                                 $tring words.      (line  5524)
* $boot:                                 $tring words.      (line  5636)
* $del:                                  $tring words.      (line  5535)
* $exec:                                 $tring words.      (line  5565)
* $free:                                 $tring words.      (line  5547)
* $init:                                 $tring words.      (line  5550)
* $ins:                                  $tring words.      (line  5538)
* $iter:                                 $tring words.      (line  5557)
* $over:                                 $tring words.      (line  5562)
* $save:                                 $tring words.      (line  5630)
* $saved:                                $tring words.      (line  5643)
* $slurp:                                $tring words.      (line  5575)
* $slurp-file:                           $tring words.      (line  5579)
* $split:                                $tring words.      (line  5553)
* $substitute:                           Substitute.        (line 11363)
* $tmp:                                  $tring words.      (line  5569)
* $unescape:                             Substitute.        (line 11378)
* $Variable:                             $tring words.      (line  5649)
* $[]:                                   $tring words.      (line  5589)
* $[]!:                                  $tring words.      (line  5593)
* $[]#:                                  $tring words.      (line  5609)
* $[]+!:                                 $tring words.      (line  5597)
* $[].:                                  $tring words.      (line  5622)
* $[]@:                                  $tring words.      (line  5605)
* $[]boot:                               $tring words.      (line  5640)
* $[]free:                               $tring words.      (line  5625)
* $[]map:                                $tring words.      (line  5612)
* $[]save:                               $tring words.      (line  5633)
* $[]saved:                              $tring words.      (line  5646)
* $[]slurp:                              $tring words.      (line  5616)
* $[]slurp-file:                         $tring words.      (line  5619)
* $[]Variable:                           $tring words.      (line  5652)
* %-prefix for binary numbers:           Literals in source code.
                                                            (line  3465)
* %align:                                Structure Glossary.
                                                            (line 12397)
* %alignment:                            Structure Glossary.
                                                            (line 12400)
* %alloc:                                Structure Glossary.
                                                            (line 12403)
* %allocate:                             Structure Glossary.
                                                            (line 12407)
* %allot:                                Structure Glossary.
                                                            (line 12411)
* %size:                                 Structure Glossary.
                                                            (line 12439)
* &-prefix for decimal numbers:          Literals in source code.
                                                            (line  3465)
* ':                                     Execution token.   (line  8106)
* '-prefix for characters/code points:   Literals in source code.
                                                            (line  3493)
* 'cold:                                 Modifying the Startup Sequence.
                                                            (line 18344)
* 's:                                    Task-local data.   (line 14769)
* (:                                     Comments.          (line  3737)
* ((:                                    Regular Expressions.
                                                            (line 13806)
* (local):                               Standard Forth locals.
                                                            (line 12159)
* (to):                                  User-defined TO and DEFER@.
                                                            (line  7521)
* ):                                     Assertions.        (line 14444)
* )):                                    Regular Expressions.
                                                            (line 13809)
* *:                                     Single precision.  (line  3811)
* **}:                                   Regular Expressions.
                                                            (line 13891)
* */:                                    Integer division.  (line  3956)
* */f:                                   Integer division.  (line  3962)
* */mod:                                 Integer division.  (line  3968)
* */modf:                                Integer division.  (line  3976)
* */mods:                                Integer division.  (line  3972)
* */s:                                   Integer division.  (line  3959)
* *align:                                Address arithmetic.
                                                            (line  5153)
* *aligned:                              Address arithmetic.
                                                            (line  5149)
* *}:                                    Regular Expressions.
                                                            (line 13903)
* +:                                     Single precision.  (line  3800)
* +!:                                    Memory Access.     (line  4880)
* +!@:                                   Hardware operations for multi-tasking.
                                                            (line 14817)
* ++}:                                   Regular Expressions.
                                                            (line 13897)
* +char:                                 Regular Expressions.
                                                            (line 13820)
* +chars:                                Regular Expressions.
                                                            (line 13829)
* +class:                                Regular Expressions.
                                                            (line 13832)
* +DO:                                   Counted Loops.     (line  5987)
* +field:                                Forth200x Structures.
                                                            (line 12491)
* +fmode:                                General files.     (line  9905)
* +load:                                 Blocks.            (line 10375)
* +LOOP:                                 Counted Loops.     (line  6034)
* +ltrace:                               Debugging.         (line 14392)
* +thru:                                 Blocks.            (line 10379)
* +TO:                                   Values.            (line  6896)
* +x/string:                             Xchars and Unicode.
                                                            (line 11240)
* +}:                                    Regular Expressions.
                                                            (line 13909)
* ,:                                     Dictionary allocation.
                                                            (line  4738)
* -:                                     Single precision.  (line  3807)
* --, tutorial:                           Stack-Effect Comments Tutorial.
                                                            (line  1255)
* --:                                    Locals definition words.
                                                            (line 11599)
* -->:                                   Blocks.            (line 10383)
* ->here:                                Dictionary allocation.
                                                            (line  4728)
* --appl-image, command-line option:      Invoking Gforth.   (line   504)
* --application, gforthmi option:         gforthmi.          (line 18166)
* -c?:                                   Regular Expressions.
                                                            (line 13845)
* -char:                                 Regular Expressions.
                                                            (line 13823)
* -class:                                Regular Expressions.
                                                            (line 13835)
* --clear-dictionary, command-line option: Invoking Gforth.  (line   583)
* -d, command-line option:               Invoking Gforth.   (line   531)
* --data-stack-size, command-line option: Invoking Gforth.   (line   531)
* --debug, command-line option:           Invoking Gforth.   (line   572)
* -DFORCE_REG:                           Portability.       (line 18409)
* --dictionary-size, command-line option: Invoking Gforth.   (line   521)
* --die-on-signal, command-line-option:   Invoking Gforth.   (line   587)
* -DO:                                   Counted Loops.     (line  6008)
* -DUSE_FTOS:                            TOS Optimization.  (line 18770)
* -DUSE_NO_FTOS:                         TOS Optimization.  (line 18770)
* -DUSE_NO_TOS:                          TOS Optimization.  (line 18758)
* -DUSE_TOS:                             TOS Optimization.  (line 18758)
* --dynamic command-line option:          Dynamic Superinstructions.
                                                            (line 18641)
* --dynamic, command-line option:         Invoking Gforth.   (line   596)
* --enable-force-reg, configuration flag: Portability.       (line 18409)
* -f, command-line option:               Invoking Gforth.   (line   541)
* --fp-stack-size, command-line option:   Invoking Gforth.   (line   541)
* -h, command-line option:               Invoking Gforth.   (line   564)
* --help, command-line option:            Invoking Gforth.   (line   564)
* -i, command-line option:               Invoking Gforth.   (line   499)
* -i, invoke image file:                 Running Image Files.
                                                            (line 18226)
* --image file, invoke image file:        Running Image Files.
                                                            (line 18226)
* --image-file, command-line option:      Invoking Gforth.   (line   499)
* -infinity:                             Floating Point.    (line  4490)
* -l, command-line option:               Invoking Gforth.   (line   547)
* --locals-stack-size, command-line option: Invoking Gforth. (line   547)
* -LOOP:                                 Counted Loops.     (line  6037)
* -ltrace:                               Debugging.         (line 14395)
* -m, command-line option:               Invoking Gforth.   (line   521)
* --no-dynamic command-line option:       Dynamic Superinstructions.
                                                            (line 18629)
* --no-dynamic, command-line option:      Invoking Gforth.   (line   596)
* --no-offset-im, command-line option:    Invoking Gforth.   (line   580)
* --no-super command-line option:         Dynamic Superinstructions.
                                                            (line 18629)
* --no-super, command-line option:        Invoking Gforth.   (line   601)
* --offset-image, command-line option:    Invoking Gforth.   (line   575)
* -p, command-line option:               Invoking Gforth.   (line   510)
* --path, command-line option:            Invoking Gforth.   (line   510)
* --print-metrics, command-line option:   Invoking Gforth.   (line   639)
* -r, command-line option:               Invoking Gforth.   (line   536)
* --return-stack-size, command-line option: Invoking Gforth. (line   536)
* -rot:                                  Data stack.        (line  4541)
* --ss-greedy, command-line option:       Invoking Gforth.   (line   626)
* --ss-min-..., command-line options:     Invoking Gforth.   (line   612)
* --ss-number, command-line option:       Invoking Gforth.   (line   606)
* -trailing:                             String words.      (line  5434)
* -trailing-garbage:                     Xchars and Unicode.
                                                            (line 11251)
* -v, command-line option:               Invoking Gforth.   (line   568)
* --version, command-line option:         Invoking Gforth.   (line   568)
* --vm-commit, command-line option:       Invoking Gforth.   (line   552)
* -W, command-line option:               Invoking Gforth.   (line   676)
* -Wall, command-line option:            Invoking Gforth.   (line   682)
* -Werror, command-line option:          Invoking Gforth.   (line   688)
* -Won, command-line option:             Invoking Gforth.   (line   679)
* -Wpedantic, command-line option:       Invoking Gforth.   (line   685)
* -[do:                                  Counted Loops.     (line  5998)
* -\d:                                   Regular Expressions.
                                                            (line 13857)
* -\s:                                   Regular Expressions.
                                                            (line 13860)
* -`:                                    Regular Expressions.
                                                            (line 13868)
* .:                                     Simple numeric output.
                                                            (line 10416)
* .":                                    Miscellaneous output.
                                                            (line 10733)
* .", how it works:                      How does that work?.
                                                            (line  3318)
* .(:                                    Miscellaneous output.
                                                            (line 10739)
* ...:                                   Examining data.    (line 14231)
* ..char:                                Regular Expressions.
                                                            (line 13826)
* .?:                                    Regular Expressions.
                                                            (line 13854)
* .cover-raw:                            Code Coverage.     (line 14589)
* .coverage:                             Code Coverage.     (line 14576)
* .debugline:                            Debugging.         (line 14352)
* .emacs:                                Installing gforth.el.
                                                            (line 17838)
* .fi files:                             Image Files.       (line 17975)
* .fpath:                                Source Search Paths.
                                                            (line 10130)
* .gforth-history:                       Command-line editing.
                                                            (line   760)
* .hm:                                   Header methods.    (line 16215)
* .id:                                   Name token.        (line  8253)
* .included:                             Forth source files.
                                                            (line  9873)
* .locale-csv:                           i18n and l10n.     (line 11334)
* .path:                                 General Search Paths.
                                                            (line 10170)
* .r:                                    Simple numeric output.
                                                            (line 10428)
* .recognizers:                          Default Recognizers.
                                                            (line  9062)
* .s:                                    Examining data.    (line 14234)
* .substitute:                           Substitute.        (line 11359)
* .unresolved:                           Forward.           (line  7899)
* .voc:                                  Word Lists.        (line  9419)
* .widget:                               widget methods.    (line 19184)
* .\":                                   Miscellaneous output.
                                                            (line 10730)
* /:                                     Integer division.  (line  3909)
* //:                                    Regular Expressions.
                                                            (line 13915)
* //g:                                   Regular Expressions.
                                                            (line 13965)
* //o:                                   Regular Expressions.
                                                            (line 13962)
* //s:                                   Regular Expressions.
                                                            (line 13959)
* /COUNTED-STRING:                       Environmental Queries.
                                                            (line  9618)
* /f:                                    Integer division.  (line  3914)
* /f-stage1m:                            Two-stage integer division.
                                                            (line  4059)
* /f-stage2m:                            Two-stage integer division.
                                                            (line  4063)
* /HOLD:                                 Environmental Queries.
                                                            (line  9621)
* /l:                                    Address arithmetic.
                                                            (line  5181)
* /mod:                                  Integer division.  (line  3927)
* /modf:                                 Integer division.  (line  3933)
* /modf-stage2m:                         Two-stage integer division.
                                                            (line  4071)
* /mods:                                 Integer division.  (line  3930)
* /PAD:                                  Environmental Queries.
                                                            (line  9624)
* /s:                                    Integer division.  (line  3912)
* /string:                               String words.      (line  5438)
* /w:                                    Address arithmetic.
                                                            (line  5178)
* /x:                                    Address arithmetic.
                                                            (line  5184)
* 0<:                                    Numeric comparison.
                                                            (line  4244)
* 0<=:                                   Numeric comparison.
                                                            (line  4246)
* 0<>:                                   Numeric comparison.
                                                            (line  4248)
* 0=:                                    Numeric comparison.
                                                            (line  4250)
* 0>:                                    Numeric comparison.
                                                            (line  4252)
* 0>=:                                   Numeric comparison.
                                                            (line  4254)
* 0x-prefix for hexadecimal numbers:     Literals in source code.
                                                            (line  3465)
* 1+:                                    Single precision.  (line  3802)
* 1-:                                    Single precision.  (line  3809)
* 1/f:                                   Floating Point.    (line  4392)
* 2!:                                    Memory Access.     (line  4893)
* 2*:                                    Bitwise operations.
                                                            (line  4164)
* 2,:                                    Dictionary allocation.
                                                            (line  4741)
* 2/:                                    Bitwise operations.
                                                            (line  4167)
* 2>r:                                   Return stack.      (line  4607)
* 2@:                                    Memory Access.     (line  4889)
* 2Constant:                             Constants.         (line  6820)
* 2drop:                                 Data stack.        (line  4549)
* 2dup:                                  Data stack.        (line  4553)
* 2field::                               Forth200x Structures.
                                                            (line 12501)
* 2Literal:                              Literals.          (line  8395)
* 2nip:                                  Data stack.        (line  4551)
* 2over:                                 Data stack.        (line  4555)
* 2r>:                                   Return stack.      (line  4609)
* 2r@:                                   Return stack.      (line  4611)
* 2rdrop:                                Return stack.      (line  4613)
* 2rot:                                  Data stack.        (line  4561)
* 2swap:                                 Data stack.        (line  4559)
* 2tuck:                                 Data stack.        (line  4557)
* 2Value:                                Values.            (line  6887)
* 2Variable:                             Variables.         (line  6779)
* 2varue:                                Varues.            (line  6911)
* ::                                     Colon Definitions. (line  6937)
* :, passing data across:                Literals.          (line  8408)
* :::                                    Basic Mini-OOF Usage.
                                                            (line 13518)
* :m:                                    Objects Glossary.  (line 13196)
* :noname:                               Anonymous Definitions.
                                                            (line  7007)
* :}:                                    Locals definition words.
                                                            (line 11608)
* :}d:                                   Closures.          (line 12072)
* :}h:                                   Closures.          (line 12076)
* :}h1:                                  Closures.          (line 12080)
* :}l:                                   Closures.          (line 12068)
* :}xt:                                  Closures.          (line 12084)
* ;:                                     Colon Definitions. (line  6939)
* ;>:                                    Closures.          (line 12136)
* ;abi-code:                             Assembler Definitions.
                                                            (line 15410)
* ;code:                                 Assembler Definitions.
                                                            (line 15433)
* ;CODE ending sequence:                 programming-idef.  (line 17553)
* ;CODE, name not defined via CREATE:    programming-ambcond.
                                                            (line 17585)
* ;CODE, processing input:               programming-idef.  (line 17556)
* ;inline:                               Colon Definitions. (line  6952)
* ;m:                                    Objects Glossary.  (line 13200)
* ;m usage:                              Method conveniences.
                                                            (line 12816)
* ;s:                                    Calls and returns. (line  6415)
* ;]:                                    Quotations.        (line  7074)
* <:                                     Numeric comparison.
                                                            (line  4232)
* <#:                                    Formatted numeric output.
                                                            (line 10497)
* <<:                                    Regular Expressions.
                                                            (line 13950)
* <<":                                   Regular Expressions.
                                                            (line 13953)
* <<#:                                   Formatted numeric output.
                                                            (line 10500)
* <=:                                    Numeric comparison.
                                                            (line  4234)
* <>:                                    Numeric comparison.
                                                            (line  4236)
* <bind>:                                Objects Glossary.  (line 13102)
* <to-inst>:                             Objects Glossary.  (line 13241)
* <{::                                   Closures.          (line 12133)
* =:                                     Numeric comparison.
                                                            (line  4238)
* =mkdir:                                Directories.       (line 10080)
* >:                                     Numeric comparison.
                                                            (line  4240)
* >=:                                    Numeric comparison.
                                                            (line  4242)
* >>:                                    Regular Expressions.
                                                            (line 13946)
* >addr:                                 Closures.          (line 12089)
* >animate:                              widget methods.    (line 19202)
* >body:                                 CREATE..DOES> details.
                                                            (line  7401)
* >BODY of non-CREATEd words:            core-ambcond.      (line 17177)
* >code-address:                         Threading Words.   (line 16448)
* >compile:                              Dealing with existing Recognizers.
                                                            (line  9209)
* >definer:                              Threading Words.   (line 16509)
* >does-code:                            Threading Words.   (line 16491)
* >float:                                Line input and conversion.
                                                            (line 11099)
* >float1:                               Line input and conversion.
                                                            (line 11107)
* >in:                                   The Text Interpreter.
                                                            (line  8751)
* >IN greater than input buffer:         core-ambcond.      (line 17109)
* >interpret:                            Dealing with existing Recognizers.
                                                            (line  9206)
* >l:                                    Locals implementation.
                                                            (line 11942)
* >name:                                 Name token.        (line  8220)
* >number:                               Line input and conversion.
                                                            (line 11086)
* >o:                                    Mini-OOF2.         (line 13693)
* >order:                                Word Lists.        (line  9394)
* >postpone:                             Dealing with existing Recognizers.
                                                            (line  9212)
* >pow2:                                 Bitwise operations.
                                                            (line  4178)
* >r:                                    Return stack.      (line  4599)
* >string-execute:                       String words.      (line  5481)
* >time&date&tz:                         Keeping track of Time.
                                                            (line 16566)
* ?:                                     Examining data.    (line 14277)
* ?!@:                                   Hardware operations for multi-tasking.
                                                            (line 14821)
* ???:                                   Debugging.         (line 14374)
* ?cov+:                                 Code Coverage.     (line 14569)
* ?DO:                                   Counted Loops.     (line  5984)
* ?dup:                                  Data stack.        (line  4543)
* ?DUP-0=-IF:                            Arbitrary control structures.
                                                            (line  6293)
* ?dup-IF:                               Arbitrary control structures.
                                                            (line  6288)
* ?events:                               Message queues.    (line 14852)
* ?EXIT:                                 Calls and returns. (line  6412)
* ?inside:                               actor methods.     (line 19055)
* ?LEAVE:                                Counted Loops.     (line  6061)
* ?of:                                   Arbitrary control structures.
                                                            (line  6314)
* @:                                     Memory Access.     (line  4874)
* @localn:                               Locals implementation.
                                                            (line 11932)
* [:                                     Literals.          (line  8374)
* [']:                                   Execution token.   (line  8110)
* [+LOOP]:                               Interpreter Directives.
                                                            (line  8967)
* [::                                    Quotations.        (line  7071)
* [?DO]:                                 Interpreter Directives.
                                                            (line  8961)
* [AGAIN]:                               Interpreter Directives.
                                                            (line  8987)
* [BEGIN]:                               Interpreter Directives.
                                                            (line  8983)
* [bind]:                                Objects Glossary.  (line 13108)
* [bind] usage:                          Class Binding.     (line 12771)
* [char]:                                String and character literals.
                                                            (line  5347)
* [COMP']:                               Compilation token. (line  8308)
* [compile]:                             Macros.            (line  8620)
* [current]:                             Objects Glossary.  (line 13141)
* [defined]:                             Interpreter Directives.
                                                            (line  8945)
* [DO]:                                  Interpreter Directives.
                                                            (line  8963)
* [ELSE]:                                Interpreter Directives.
                                                            (line  8929)
* [ENDIF]:                               Interpreter Directives.
                                                            (line  8942)
* [FOR]:                                 Interpreter Directives.
                                                            (line  8969)
* [IFDEF]:                               Interpreter Directives.
                                                            (line  8951)
* [IFUNDEF]:                             Interpreter Directives.
                                                            (line  8956)
* [IF]:                                  Interpreter Directives.
                                                            (line  8921)
* [IF] and POSTPONE:                     programming-ambcond.
                                                            (line 17590)
* [IF], end of the input source before matching [ELSE] or [THEN]: programming-ambcond.
                                                            (line 17594)
* [I]:                                   Interpreter Directives.
                                                            (line  8973)
* [LOOP]:                                Interpreter Directives.
                                                            (line  8965)
* [NEXT]:                                Interpreter Directives.
                                                            (line  8971)
* [parent]:                              Objects Glossary.  (line 13219)
* [parent] usage:                        Class Binding.     (line 12790)
* [REPEAT]:                              Interpreter Directives.
                                                            (line  8991)
* [THEN]:                                Interpreter Directives.
                                                            (line  8938)
* [to-inst]:                             Objects Glossary.  (line 13244)
* [undefined]:                           Interpreter Directives.
                                                            (line  8948)
* [UNTIL]:                               Interpreter Directives.
                                                            (line  8985)
* [WHILE]:                               Interpreter Directives.
                                                            (line  8989)
* [{::                                   Closures.          (line 12057)
* \:                                     Comments.          (line  3744)
* \$:                                    Regular Expressions.
                                                            (line 13877)
* \(:                                    Regular Expressions.
                                                            (line 13932)
* \):                                    Regular Expressions.
                                                            (line 13935)
* \, editing with Emacs:                 Emacs and Gforth.  (line 17807)
* \, line length in blocks:              block-idef.        (line 17228)
* \0:                                    Regular Expressions.
                                                            (line 13938)
* \c:                                    Declaring C Functions.
                                                            (line 15062)
* \d:                                    Regular Expressions.
                                                            (line 13848)
* \G:                                    Comments.          (line  3750)
* \s:                                    Regular Expressions.
                                                            (line 13851)
* \\\:                                   Forth source files.
                                                            (line  9870)
* \^:                                    Regular Expressions.
                                                            (line 13874)
* ]:                                     Literals.          (line  8377)
* ]L:                                    Literals.          (line  8389)
* ]nocov:                                Code Coverage.     (line 14560)
* ]]:                                    Macros.            (line  8464)
* `:                                     Regular Expressions.
                                                            (line 13863)
* ` prefix:                              Execution token.   (line  8096)
* ` prefix of word:                      Literals in source code.
                                                            (line  3563)
* `?:                                    Regular Expressions.
                                                            (line 13866)
* `` prefix of word:                     Literals in source code.
                                                            (line  3569)
* {:                                     Locals definition words.
                                                            (line 11611)
* {*:                                    Regular Expressions.
                                                            (line 13900)
* {**:                                   Regular Expressions.
                                                            (line 13888)
* {+:                                    Regular Expressions.
                                                            (line 13906)
* {++:                                   Regular Expressions.
                                                            (line 13894)
* {::                                    Locals definition words.
                                                            (line 11596)
* {{:                                    Regular Expressions.
                                                            (line 13920)
* |:                                     Locals definition words.
                                                            (line 11604)
* ||:                                    Regular Expressions.
                                                            (line 13923)
* }:                                     Locals definition words.
                                                            (line 11615)
* }}:                                    Regular Expressions.
                                                            (line 13926)
* ~~:                                    Debugging.         (line 14346)
* ~~, removal with Emacs:                Emacs and Gforth.  (line 17807)
* ~~1bt:                                 Debugging.         (line 14371)
* ~~bt:                                  Debugging.         (line 14368)
* ~~Value:                               Debugging.         (line 14389)
* ~~Variable:                            Debugging.         (line 14386)
* A,:                                    Dictionary allocation.
                                                            (line  4753)
* abi-code:                              Assembler Definitions.
                                                            (line 15402)
* abort:                                 Exception Handling.
                                                            (line  6664)
* ABORT":                                Exception Handling.
                                                            (line  6659)
* ABORT", exception abort sequence:      core-idef.         (line 16881)
* abs:                                   Single precision.  (line  3815)
* absolute-file?:                        Search Paths.      (line 10115)
* abstract class:                        Basic Objects Usage.
                                                            (line 12671)
* abstract class <1>:                    Basic OOF Usage.   (line 13309)
* accept:                                Line input and conversion.
                                                            (line 11067)
* ACCEPT, display after end of input:    core-idef.         (line 16877)
* ACCEPT, editing:                       core-idef.         (line 16823)
* AConstant:                             Constants.         (line  6816)
* act:                                   widget methods.    (line 19091)
* act-name$:                             actor methods.     (line 19034)
* action-of:                             Deferred Words.    (line  7868)
* activate:                              Basic multi-tasking.
                                                            (line 14676)
* active-w:                              actor methods.     (line 19031)
* actor:                                 MINOS2 object framework.
                                                            (line 19019)
* add-cflags:                            Declaring OS-level libraries.
                                                            (line 15215)
* add-framework:                         Declaring OS-level libraries.
                                                            (line 15208)
* add-incdir:                            Declaring OS-level libraries.
                                                            (line 15212)
* add-ldflags:                           Declaring OS-level libraries.
                                                            (line 15218)
* add-lib:                               Declaring OS-level libraries.
                                                            (line 15200)
* add-libpath:                           Declaring OS-level libraries.
                                                            (line 15204)
* addr:                                  Varues.            (line  6919)
* address alignment exception:           core-ambcond.      (line 17130)
* address alignment exception, stack overflow: core-ambcond.
                                                            (line 17032)
* address arithmetic for structures:     Why explicit structure support?.
                                                            (line 12187)
* address arithmetic words:              Address arithmetic.
                                                            (line  5038)
* address unit:                          Address arithmetic.
                                                            (line  5042)
* address unit, size in bits:            core-idef.         (line 16917)
* ADDRESS-UNIT-BITS:                     Environmental Queries.
                                                            (line  9612)
* adjust-buffer:                         Heap Allocation.   (line  4856)
* after-locate:                          Locating source code definitions.
                                                            (line 14027)
* AGAIN:                                 Arbitrary control structures.
                                                            (line  6247)
* AHEAD:                                 Arbitrary control structures.
                                                            (line  6231)
* Alias:                                 Aliases.           (line  7926)
* aliases:                               Aliases.           (line  7905)
* align:                                 Dictionary allocation.
                                                            (line  4772)
* aligned:                               Address arithmetic.
                                                            (line  5096)
* aligned addresses:                     core-idef.         (line 16813)
* alignment faults:                      core-ambcond.      (line 17130)
* alignment of addresses for types:      Address arithmetic.
                                                            (line  5053)
* alignment tutorial:                    Alignment Tutorial.
                                                            (line  1991)
* ALiteral:                              Literals.          (line  8385)
* allocate:                              Heap Allocation.   (line  4808)
* allot:                                 Dictionary allocation.
                                                            (line  4721)
* also:                                  Word Lists.        (line  9400)
* also, too many word lists in search order: search-ambcond.
                                                            (line 17628)
* also-path:                             General Search Paths.
                                                            (line 10167)
* ambiguous conditions, block words:     block-ambcond.     (line 17233)
* ambiguous conditions, core words:      core-ambcond.      (line 16997)
* ambiguous conditions, double words:    double-ambcond.    (line 17269)
* ambiguous conditions, facility words:  facility-ambcond.  (line 17314)
* ambiguous conditions, file words:      file-ambcond.      (line 17381)
* ambiguous conditions, floating-point words: floating-ambcond.
                                                            (line 17440)
* ambiguous conditions, locals words:    locals-ambcond.    (line 17526)
* ambiguous conditions, programming-tools words: programming-ambcond.
                                                            (line 17572)
* ambiguous conditions, search-order words: search-ambcond. (line 17616)
* and:                                   Bitwise operations.
                                                            (line  4129)
* angles in trigonometric operations:    Floating Point.    (line  4405)
* annotate-cov:                          Code Coverage.     (line 14579)
* ans-report.fs:                         Standard Report.   (line 16671)
* append:                                String words.      (line  5476)
* arg:                                   OS command line arguments.
                                                            (line 11431)
* argc:                                  OS command line arguments.
                                                            (line 11445)
* argument input source different than current input source for RESTORE-INPUT: core-ambcond.
                                                            (line 17116)
* argument type mismatch:                core-ambcond.      (line 17010)
* argument type mismatch, RESTORE-INPUT: core-ambcond.      (line 17116)
* arguments, OS command line:            OS command line arguments.
                                                            (line 11396)
* argv:                                  OS command line arguments.
                                                            (line 11449)
* arithmetic words:                      Arithmetic.        (line  3780)
* arithmetics tutorial:                  Arithmetics Tutorial.
                                                            (line  1051)
* array, iterating over:                 Counted Loops.     (line  5931)
* arrays:                                CREATE.            (line  6731)
* arrays tutorial:                       Arrays and Records Tutorial.
                                                            (line  2506)
* arshift:                               Bitwise operations.
                                                            (line  4149)
* asptr:                                 Class Declaration. (line 13449)
* assembler:                             Assembler and Code Words.
                                                            (line 15366)
* assembler <1>:                         Assembler Definitions.
                                                            (line 15395)
* ASSEMBLER, search order capability:    programming-idef.  (line 17561)
* assert(:                               Assertions.        (line 14441)
* assert-level:                          Assertions.        (line 14460)
* assert0(:                              Assertions.        (line 14428)
* assert1(:                              Assertions.        (line 14431)
* assert2(:                              Assertions.        (line 14434)
* assert3(:                              Assertions.        (line 14437)
* assertions:                            Assertions.        (line 14404)
* ASSUME-LIVE:                           Where are locals visible by name?.
                                                            (line 11804)
* at-deltaxy:                            Terminal output.   (line 10806)
* at-xy:                                 Terminal output.   (line 10802)
* AT-XY can't be performed on user output device: facility-ambcond.
                                                            (line 17315)
* Attempt to use zero-length string as a name: core-ambcond.
                                                            (line 17103)
* au (address unit):                     Address arithmetic.
                                                            (line  5042)
* AUser:                                 Task-local data.   (line 14743)
* authors:                               Help on Gforth.    (line   716)
* authors of Gforth:                     Origin.            (line 19333)
* auto-indentation of Forth code in Emacs: Auto-Indentation.
                                                            (line 17911)
* AValue:                                Values.            (line  6883)
* AVariable:                             Variables.         (line  6775)
* a_, stack item type:                   Notation.          (line  3679)
* b:                                     Locating source code definitions.
                                                            (line 14013)
* backtrace:                             Error messages.    (line 16603)
* backtrace examination:                 Locating exception source.
                                                            (line 14101)
* backtraces with gforth-fast:           Error messages.    (line 16650)
* barrier:                               Hardware operations for multi-tasking.
                                                            (line 14830)
* base:                                  Number Conversion. (line  8855)
* base is not decimal (REPRESENT, F., FE., FS.): floating-ambcond.
                                                            (line 17460)
* base-execute:                          Number Conversion. (line  8851)
* baseline:                              widget methods.    (line 19115)
* basename:                              Directories.       (line 10037)
* basic objects usage:                   Basic Objects Usage.
                                                            (line 12657)
* batch processing with Gforth:          Invoking Gforth.   (line   650)
* before-line:                           Text Interpreter Hooks.
                                                            (line  9230)
* before-locate:                         Locating source code definitions.
                                                            (line 14024)
* before-word:                           Text Interpreter Hooks.
                                                            (line  9233)
* BEGIN:                                 Arbitrary control structures.
                                                            (line  6239)
* begin-structure:                       Forth200x Structures.
                                                            (line 12482)
* benchmarking Forth systems:            Performance.       (line 18803)
* Benchres:                              Performance.       (line 18883)
* big-endian:                            Special Memory Accesses.
                                                            (line  4921)
* bin:                                   General files.     (line  9903)
* bind:                                  Objects Glossary.  (line 13099)
* bind usage:                            Class Binding.     (line 12775)
* bind':                                 Objects Glossary.  (line 13105)
* bitwise operation words:               Bitwise operations.
                                                            (line  4129)
* bl:                                    String and character literals.
                                                            (line  5374)
* blank:                                 Memory Blocks.     (line  5224)
* blk:                                   Input Sources.     (line  8806)
* BLK, altering BLK:                     block-ambcond.     (line 17246)
* block:                                 Blocks.            (line 10331)
* block buffers:                         Blocks.            (line 10225)
* block number invalid:                  block-ambcond.     (line 17243)
* block read not possible:               block-ambcond.     (line 17234)
* block transfer, I/O exception:         block-ambcond.     (line 17239)
* block words, ambiguous conditions:     block-ambcond.     (line 17233)
* block words, implementation-defined options: block-idef.  (line 17223)
* block words, other system documentation: block-other.     (line 17257)
* block words, system documentation:     The optional Block word set.
                                                            (line 17220)
* block-included:                        Blocks.            (line 10390)
* block-offset:                          Blocks.            (line 10310)
* block-position:                        Blocks.            (line 10320)
* blocks:                                Blocks.            (line 10191)
* blocks file:                           Blocks.            (line 10214)
* blocks files, use with Emacs:          Blocks Files.      (line 17947)
* blocks in files:                       file-idef.         (line 17368)
* blocks.fb:                             Blocks.            (line 10220)
* body-relative address input format:    Literals in source code.
                                                            (line  3572)
* Boolean flags:                         Boolean Flags.     (line  3757)
* bootmessage:                           Modifying the Startup Sequence.
                                                            (line 18349)
* border:                                widget methods.    (line 19124)
* borderl:                               widget methods.    (line 19133)
* bordert:                               widget methods.    (line 19130)
* borderv:                               widget methods.    (line 19127)
* bounds:                                Counted Loops.     (line  5993)
* break":                                Singlestep Debugger.
                                                            (line 14541)
* break::                                Singlestep Debugger.
                                                            (line 14539)
* broken-pipe-error:                     Pipes.             (line 11150)
* browse:                                Locating source code definitions.
                                                            (line 14038)
* bt:                                    Locating exception source.
                                                            (line 14105)
* buffer:                                Blocks.            (line 10338)
* buffer%:                               Heap Allocation.   (line  4851)
* buffer::                               Variables.         (line  6785)
* bug reporting:                         Bugs.              (line 19306)
* bw:                                    Locating uses of a word.
                                                            (line 14061)
* bw-cover:                              Code Coverage.     (line 14596)
* bye during gforthmi:                   gforthmi.          (line 18176)
* byte order:                            Special Memory Accesses.
                                                            (line  4921)
* C function pointers to Forth words:    Callbacks.         (line 15224)
* C function pointers, calling from Forth: Calling C function pointers.
                                                            (line 15087)
* C functions, calls to:                 Calling C Functions.
                                                            (line 14932)
* C functions, declarations:             Declaring C Functions.
                                                            (line 14992)
* C interface:                           C Interface.       (line 14916)
* c!:                                    Memory Access.     (line  4886)
* C":                                    Counted string words.
                                                            (line  5673)
* c$+!:                                  $tring words.      (line  5544)
* c,:                                    Dictionary allocation.
                                                            (line  4731)
* c, stack item type:                    Notation.          (line  3665)
* C, using C for the engine:             Portability.       (line 18382)
* c-callback:                            Callbacks.         (line 15234)
* c-callback-thread:                     Callbacks.         (line 15239)
* c-function:                            Declaring C Functions.
                                                            (line 15065)
* c-funptr:                              Calling C function pointers.
                                                            (line 15092)
* c-library:                             Defining library interfaces.
                                                            (line 15164)
* c-library-name:                        Defining library interfaces.
                                                            (line 15161)
* c-value:                               Declaring C Functions.
                                                            (line 15069)
* c-variable:                            Declaring C Functions.
                                                            (line 15073)
* C::                                    Locals definition words.
                                                            (line 11637)
* c>s:                                   Special Memory Accesses.
                                                            (line  5015)
* c?:                                    Regular Expressions.
                                                            (line 13842)
* c@:                                    Memory Access.     (line  4883)
* CA::                                   Locals definition words.
                                                            (line 11640)
* call-c:                                Low-Level C Interface Words.
                                                            (line 15289)
* Callback functions written in Forth:   Callbacks.         (line 15224)
* caller-w:                              actor methods.     (line 19028)
* calling a definition:                  Calls and returns. (line  6366)
* calling C functions:                   Calling C Functions.
                                                            (line 14932)
* capscompare:                           String words.      (line  5455)
* capssearch:                            String words.      (line  5466)
* capsstring-prefix?:                    String words.      (line  5462)
* case:                                  Arbitrary control structures.
                                                            (line  6297)
* case as generalized control structure: General control structures with CASE.
                                                            (line  6140)
* CASE control structure:                Selection.         (line  5735)
* case sensitivity:                      Case insensitivity.
                                                            (line  3705)
* case-sensitivity characteristics:      core-idef.         (line 16962)
* case-sensitivity for name lookup:      core-idef.         (line 16840)
* catch:                                 Exception Handling.
                                                            (line  6498)
* catch and backtraces:                  Error messages.    (line 16639)
* catch and this:                        Objects Implementation.
                                                            (line 13022)
* catch in m: ... ;m:                    Method conveniences.
                                                            (line 12819)
* cell:                                  Address arithmetic.
                                                            (line  5093)
* cell size:                             core-idef.         (line 16942)
* cell%:                                 Structure Glossary.
                                                            (line 12415)
* cell+:                                 Address arithmetic.
                                                            (line  5084)
* cell-:                                 Address arithmetic.
                                                            (line  5087)
* cell-aligned addresses:                core-idef.         (line 16813)
* cell/:                                 Address arithmetic.
                                                            (line  5090)
* cells:                                 Address arithmetic.
                                                            (line  5081)
* CFA:                                   Threading Words.   (line 16381)
* cfalign:                               Dictionary allocation.
                                                            (line  4791)
* cfaligned:                             Address arithmetic.
                                                            (line  5145)
* cfield::                               Forth200x Structures.
                                                            (line 12495)
* changing the compilation word list (during compilation): search-ambcond.
                                                            (line 17617)
* char:                                  String and character literals.
                                                            (line  5343)
* char size:                             core-idef.         (line 16945)
* char%:                                 Structure Glossary.
                                                            (line 12417)
* char+:                                 Address arithmetic.
                                                            (line  5076)
* char-:                                 Address arithmetic.
                                                            (line  5079)
* character editing of ACCEPT and EXPECT: core-idef.        (line 16823)
* character encoding:                    Characters.        (line  5251)
* character literals:                    String and character literals.
                                                            (line  5304)
* character set:                         core-idef.         (line 16830)
* character strings - displaying:        Displaying characters and strings.
                                                            (line 10782)
* character strings - moving and copying: Memory Blocks.    (line  5190)
* character strings - representations:   String representations.
                                                            (line  5281)
* character-aligned address requirements: core-idef.        (line 16835)
* character-set extensions and matching of names: core-idef.
                                                            (line 16840)
* Characters - chars/bytes vs. extended characters: Characters.
                                                            (line  5251)
* characters - displaying:               Displaying characters and strings.
                                                            (line 10782)
* characters tutorial:                   Characters and Strings Tutorial.
                                                            (line  1942)
* charclass:                             Regular Expressions.
                                                            (line 13817)
* chars:                                 Address arithmetic.
                                                            (line  5073)
* child class:                           Object-Oriented Terminology.
                                                            (line 12597)
* child words:                           User-defined defining words using CREATE.
                                                            (line  7182)
* cilk-bye:                              Cilk.              (line 14910)
* cilk-init:                             Cilk.              (line 14892)
* cilk-sync:                             Cilk.              (line 14907)
* class:                                 Object-Oriented Terminology.
                                                            (line 12564)
* class <1>:                             Objects Glossary.  (line 13111)
* class <2>:                             Basic Mini-OOF Usage.
                                                            (line 13506)
* class binding:                         Class Binding.     (line 12762)
* class binding as optimization:         Class Binding.     (line 12795)
* class binding, alternative to:         Class Binding.     (line 12777)
* class binding, implementation:         Objects Implementation.
                                                            (line 13018)
* class declaration:                     Class Declaration. (line 13439)
* class definition, restrictions:        Basic Objects Usage.
                                                            (line 12709)
* class definition, restrictions <1>:    Basic OOF Usage.   (line 13342)
* class implementation:                  Class Implementation.
                                                            (line 13480)
* class implementation and representation: Objects Implementation.
                                                            (line 13003)
* class scoping implementation:          Objects Implementation.
                                                            (line 13037)
* class usage:                           Basic Objects Usage.
                                                            (line 12659)
* class usage <1>:                       Basic OOF Usage.   (line 13297)
* class->map:                            Objects Glossary.  (line 13115)
* class-inst-size:                       Objects Glossary.  (line 13120)
* class-inst-size discussion:            Creating objects.  (line 12734)
* class-override!:                       Objects Glossary.  (line 13124)
* class-previous:                        Objects Glossary.  (line 13127)
* class;:                                Class Declaration. (line 13475)
* class; usage:                          Basic OOF Usage.   (line 13297)
* class>order:                           Objects Glossary.  (line 13131)
* classes and scoping:                   Classes and Scoping.
                                                            (line 12875)
* clear screen:                          Terminal output.   (line 10814)
* clear-libs:                            Declaring OS-level libraries.
                                                            (line 15197)
* clear-path:                            General Search Paths.
                                                            (line 10164)
* clearstack:                            Examining data.    (line 14266)
* clearstacks:                           Examining data.    (line 14272)
* clicked:                               actor methods.     (line 19037)
* clock tick duration:                   facility-idef.     (line 17301)
* close-dir:                             Directories.       (line 10064)
* close-file:                            General files.     (line  9917)
* close-pipe:                            Pipes.             (line 11141)
* closures:                              Closures.          (line 12049)
* cmove:                                 Memory Blocks.     (line  5208)
* cmove>:                                Memory Blocks.     (line  5213)
* code:                                  Assembler Definitions.
                                                            (line 15426)
* code address:                          Threading Words.   (line 16381)
* code coverage:                         Code Coverage.     (line 14546)
* CODE ending sequence:                  programming-idef.  (line 17553)
* code field:                            Threading Words.   (line 16381)
* code words:                            Assembler and Code Words.
                                                            (line 15366)
* CODE, processing input:                programming-idef.  (line 17556)
* code-address!:                         Threading Words.   (line 16451)
* colon definitions:                     Colon Definitions. (line  6926)
* colon definitions <1>:                 Anonymous Definitions.
                                                            (line  7004)
* colon definitions, nesting:            Quotations.        (line  7050)
* colon definitions, tutorial:           Colon Definitions Tutorial.
                                                            (line  1206)
* colon-sys, passing data across ::      Literals.          (line  8408)
* color-cover:                           Code Coverage.     (line 14599)
* color::                                widget methods.    (line 19210)
* combined words:                        Combined words.    (line  8017)
* command line arguments, OS:            OS command line arguments.
                                                            (line 11396)
* command-line editing:                  Command-line editing.
                                                            (line   725)
* command-line options:                  Invoking Gforth.   (line   473)
* comment editing commands:              Emacs and Gforth.  (line 17807)
* comments:                              Comments.          (line  3734)
* comments tutorial:                     Comments Tutorial. (line  1177)
* common-list:                           Locals implementation.
                                                            (line 12012)
* COMP':                                 Compilation token. (line  8311)
* comp-i.fs:                             gforthmi.          (line 18138)
* comp.lang.forth:                       Forth-related information.
                                                            (line 19394)
* compare:                               Memory Blocks.     (line  5235)
* comparison of object models:           Comparison with other object models.
                                                            (line 13714)
* comparison tutorial:                   Flags and Comparisons Tutorial.
                                                            (line  1530)
* compilation semantics:                 How does that work?.
                                                            (line  3231)
* compilation semantics <1>:             Interpretation and Compilation Semantics.
                                                            (line  7952)
* compilation semantics tutorial:        Interpretation and Compilation Semantics and Immediacy Tutorial.
                                                            (line  2199)
* compilation token:                     Compilation token. (line  8291)
* compilation tokens, tutorial:          Compilation Tokens Tutorial.
                                                            (line  2668)
* compilation word list:                 Word Lists.        (line  9339)
* compilation word list, change before definition ends: search-ambcond.
                                                            (line 17617)
* compile state:                         The Text Interpreter.
                                                            (line  8641)
* compile,:                              Macros.            (line  8575)
* compile-lp+!:                          Locals implementation.
                                                            (line 11952)
* compile-only:                          Interpretation and Compilation Semantics.
                                                            (line  7991)
* compile-only warning, for ' etc.:      core-ambcond.      (line 17015)
* compile-only words:                    Interpretation and Compilation Semantics.
                                                            (line  7985)
* compile-only?:                         Header fields.     (line 16169)
* compiled code examination:             Examining compiled code.
                                                            (line 14110)
* compiling compilation semantics:       Macros.            (line  8424)
* compiling words:                       Compiling words.   (line  8333)
* conditional compilation:               Interpreter Directives.
                                                            (line  8907)
* conditionals, tutorial:                Conditional execution Tutorial.
                                                            (line  1484)
* const-does>:                           Const-does>.       (line  7749)
* Constant:                              Constants.         (line  6811)
* constants:                             Constants.         (line  6793)
* construct:                             Objects Glossary.  (line 13134)
* construct discussion:                  Creating objects.  (line 12728)
* context:                               Word Lists.        (line  9484)
* context-sensitive help:                Emacs and Gforth.  (line 17830)
* contiguous regions and heap allocation: Heap Allocation.  (line  4798)
* contiguous regions in dictionary allocation: Dictionary allocation.
                                                            (line  4700)
* contof:                                Arbitrary control structures.
                                                            (line  6321)
* contributors to Gforth:                Origin.            (line 19333)
* control characters as delimiters:      core-idef.         (line 16856)
* control structures:                    Control Structures.
                                                            (line  5685)
* control structures for selection:      Selection.         (line  5698)
* control structures programming style:  Arbitrary control structures.
                                                            (line  6330)
* control structures, user-defined:      Arbitrary control structures.
                                                            (line  6216)
* control-flow stack:                    Arbitrary control structures.
                                                            (line  6216)
* control-flow stack items, locals information: Locals implementation.
                                                            (line 12002)
* control-flow stack underflow:          programming-ambcond.
                                                            (line 17576)
* control-flow stack, format:            core-idef.         (line 16864)
* convert:                               Line input and conversion.
                                                            (line 11117)
* convertin strings to numbers:          Line input and conversion.
                                                            (line 11062)
* CORE:                                  Environmental Queries.
                                                            (line  9627)
* core words, ambiguous conditions:      core-ambcond.      (line 16997)
* core words, implementation-defined options: core-idef.    (line 16812)
* core words, other system documentation: core-other.       (line 17189)
* core words, system documentation:      The Core Words.    (line 16809)
* CORE-EXT:                              Environmental Queries.
                                                            (line  9631)
* cores:                                 Cilk.              (line 14886)
* count:                                 Counted string words.
                                                            (line  5665)
* counted loops:                         Counted Loops.     (line  5813)
* counted loops with negative increment: Counted Loops.     (line  5884)
* counted string, maximum size:          core-idef.         (line 16890)
* counted strings:                       String representations.
                                                            (line  5281)
* Country:                               i18n and l10n.     (line 11312)
* cov%:                                  Code Coverage.     (line 14585)
* cov+:                                  Code Coverage.     (line 14566)
* coverage?:                             Code Coverage.     (line 14563)
* cputime:                               Keeping track of Time.
                                                            (line 16578)
* cr:                                    Miscellaneous output.
                                                            (line 10710)
* Create:                                CREATE.            (line  6709)
* CREATE ... DOES>:                      User-defined defining words using CREATE.
                                                            (line  7171)
* CREATE ... DOES>, applications:        CREATE..DOES> applications.
                                                            (line  7295)
* CREATE ... DOES>, details:             CREATE..DOES> details.
                                                            (line  7332)
* CREATE ... SET-DOES>:                  User-defined defining words using CREATE.
                                                            (line  7222)
* CREATE and alignment:                  Address arithmetic.
                                                            (line  5066)
* create-file:                           General files.     (line  9915)
* create-from:                           Creating from a prototype.
                                                            (line  7701)
* create...does> tutorial:               Defining Words Tutorial.
                                                            (line  2417)
* creating objects:                      Creating objects.  (line 12728)
* critical-section:                      Semaphores.        (line 14800)
* cross-compiler:                        cross.fs.          (line 18191)
* cross-compiler <1>:                    Cross Compiler.    (line 18896)
* cross.fs:                              cross.fs.          (line 18191)
* cross.fs <1>:                          Cross Compiler.    (line 18896)
* CS-DROP:                               Arbitrary control structures.
                                                            (line  6255)
* CS-PICK:                               Arbitrary control structures.
                                                            (line  6251)
* CS-PICK, fewer than u+1 items on the control flow-stack: programming-ambcond.
                                                            (line 17576)
* CS-ROLL:                               Arbitrary control structures.
                                                            (line  6253)
* CS-ROLL, fewer than u+1 items on the control flow-stack: programming-ambcond.
                                                            (line 17576)
* cs-vocabulary:                         Word Lists.        (line  9391)
* cs-wordlist:                           Word Lists.        (line  9388)
* cstring>sstring:                       String words.      (line  5447)
* ct (compilation token):                Compilation token. (line  8291)
* CT, tutorial:                          Compilation Tokens Tutorial.
                                                            (line  2668)
* ctz:                                   Bitwise operations.
                                                            (line  4189)
* current:                               Word Lists.        (line  9481)
* current':                              Objects Glossary.  (line 13138)
* current-interface:                     Objects Glossary.  (line 13144)
* current-interface discussion:          Objects Implementation.
                                                            (line 13003)
* currying:                              CREATE..DOES> applications.
                                                            (line  7316)
* cursor positioning:                    Terminal output.   (line 10800)
* C^:                                    Locals definition words.
                                                            (line 11643)
* c_, stack item type:                   Notation.          (line  3681)
* d:                                     widget methods.    (line 19109)
* d+:                                    Double precision.  (line  3847)
* d, stack item type:                    Notation.          (line  3673)
* d-:                                    Double precision.  (line  3849)
* d.:                                    Simple numeric output.
                                                            (line 10441)
* d.r:                                   Simple numeric output.
                                                            (line 10449)
* d0<:                                   Numeric comparison.
                                                            (line  4285)
* d0<=:                                  Numeric comparison.
                                                            (line  4287)
* d0<>:                                  Numeric comparison.
                                                            (line  4289)
* d0=:                                   Numeric comparison.
                                                            (line  4291)
* d0>:                                   Numeric comparison.
                                                            (line  4293)
* d0>=:                                  Numeric comparison.
                                                            (line  4295)
* d2*:                                   Bitwise operations.
                                                            (line  4171)
* d2/:                                   Bitwise operations.
                                                            (line  4174)
* D::                                    Locals definition words.
                                                            (line 11628)
* d<:                                    Numeric comparison.
                                                            (line  4273)
* d<=:                                   Numeric comparison.
                                                            (line  4275)
* d<>:                                   Numeric comparison.
                                                            (line  4277)
* d=:                                    Numeric comparison.
                                                            (line  4279)
* d>:                                    Numeric comparison.
                                                            (line  4281)
* d>=:                                   Numeric comparison.
                                                            (line  4283)
* d>f:                                   Floating Point.    (line  4328)
* D>F, d cannot be presented precisely as a float: floating-ambcond.
                                                            (line 17472)
* d>s:                                   Double precision.  (line  3845)
* D>S, d out of range of n:              double-ambcond.    (line 17270)
* DA::                                   Locals definition words.
                                                            (line 11631)
* dabs:                                  Double precision.  (line  3853)
* dark-mode:                             Terminal output.   (line 10865)
* darshift:                              Bitwise operations.
                                                            (line  4160)
* data space - reserving some:           Dictionary allocation.
                                                            (line  4696)
* data space available:                  core-other.        (line 17199)
* data space containing definitions gets de-allocated: core-ambcond.
                                                            (line 17126)
* data space pointer not properly aligned, ,, C,: core-ambcond.
                                                            (line 17138)
* data space read/write with incorrect alignment: core-ambcond.
                                                            (line 17130)
* data stack:                            Stack Manipulation.
                                                            (line  4507)
* data stack manipulation words:         Data stack.        (line  4520)
* data structure locals:                 Gforth locals.     (line 11562)
* data-relocatable image files:          Data-Relocatable Image Files.
                                                            (line 18108)
* data-space, read-only regions:         core-idef.         (line 16932)
* dbg:                                   Singlestep Debugger.
                                                            (line 14537)
* debug tracer editing commands:         Emacs and Gforth.  (line 17807)
* debug-fid:                             Debugging.         (line 14357)
* debugging:                             Debugging.         (line 14324)
* debugging output, finding the source location in Emacs: Emacs and Gforth.
                                                            (line 17822)
* debugging Singlestep:                  Singlestep Debugger.
                                                            (line 14480)
* dec.:                                  Simple numeric output.
                                                            (line 10420)
* dec.r:                                 Simple numeric output.
                                                            (line 10438)
* decimal:                               Number Conversion. (line  8864)
* declaring C functions:                 Declaring C Functions.
                                                            (line 14992)
* decompilation tutorial:                Decompilation Tutorial.
                                                            (line  1238)
* default type of locals:                Gforth locals.     (line 11546)
* default-color:                         Terminal output.   (line 10829)
* default-w::                            Gforth locals.     (line 11553)
* default-wa::                           Gforth locals.     (line 11549)
* Defer:                                 Deferred Words.    (line  7854)
* defer:                                 Class Declaration. (line 13454)
* defer!:                                Deferred Words.    (line  7858)
* defer@:                                Deferred Words.    (line  7864)
* deferred words:                        Deferred Words.    (line  7781)
* defers:                                Deferred Words.    (line  7874)
* definer:                               Threading Words.   (line 16506)
* definer!:                              Threading Words.   (line 16514)
* defines:                               Basic Mini-OOF Usage.
                                                            (line 13512)
* defining defining words:               User-defined Defining Words.
                                                            (line  7101)
* defining words:                        Defining Words.    (line  6690)
* defining words tutorial:               Defining Words Tutorial.
                                                            (line  2417)
* defining words without name:           Anonymous Definitions.
                                                            (line  7004)
* defining words, name given in a string: Supplying names.  (line  7080)
* defining words, simple:                CREATE.            (line  6696)
* defining words, user-defined:          User-defined Defining Words.
                                                            (line  7101)
* definition:                            Introducing the Text Interpreter.
                                                            (line  2838)
* definitions:                           Word Lists.        (line  9358)
* definitions, tutorial:                 Colon Definitions Tutorial.
                                                            (line  1206)
* defocus:                               actor methods.     (line 19061)
* delete:                                Memory Blocks.     (line  5231)
* delete-file:                           General files.     (line  9919)
* delta-i:                               Counted Loops.     (line  6055)
* depth:                                 Examining data.    (line 14258)
* depth changes during interpretation:   Stack depth changes.
                                                            (line 16714)
* depth-changes.fs:                      Stack depth changes.
                                                            (line 16714)
* design of stack effects, tutorial:     Designing the stack effect Tutorial.
                                                            (line  1402)
* dest, control-flow stack item:         Arbitrary control structures.
                                                            (line  6221)
* df!:                                   Memory Access.     (line  4914)
* df@:                                   Memory Access.     (line  4910)
* df@ or df! used with an address that is not double-float aligned: floating-ambcond.
                                                            (line 17441)
* dfalign:                               Dictionary allocation.
                                                            (line  4784)
* dfaligned:                             Address arithmetic.
                                                            (line  5137)
* dffield::                              Forth200x Structures.
                                                            (line 12510)
* dfloat%:                               Structure Glossary.
                                                            (line 12419)
* dfloat+:                               Address arithmetic.
                                                            (line  5132)
* dfloat/:                               Address arithmetic.
                                                            (line  5135)
* dfloats:                               Address arithmetic.
                                                            (line  5128)
* df_, stack item type:                  Notation.          (line  3686)
* dglue:                                 widget methods.    (line 19154)
* dglue@:                                widget methods.    (line 19163)
* dict-new:                              Objects Glossary.  (line 13147)
* dict-new discussion:                   Creating objects.  (line 12728)
* dictionary:                            The Text Interpreter.
                                                            (line  8658)
* dictionary in persistent form:         Image Files.       (line 17975)
* dictionary overflow:                   core-ambcond.      (line 17048)
* dictionary size default:               Stack and Dictionary Sizes.
                                                            (line 18205)
* digits > 35:                           core-idef.         (line 16873)
* direct threaded inner interpreter:     Threading.         (line 18440)
* Directories:                           Directories.       (line 10035)
* dirname:                               Directories.       (line 10041)
* disassembler, general:                 Common Disassembler.
                                                            (line 15568)
* discode:                               Common Disassembler.
                                                            (line 15571)
* dispose-widget:                        widget methods.    (line 19181)
* dividing by zero:                      core-ambcond.      (line 17027)
* dividing by zero, floating-point:      floating-ambcond.  (line 17475)
* Dividing classes:                      Dividing classes.  (line 12901)
* dividing integers:                     Integer division.  (line  3871)
* dividing many integers with the same divisor: Two-stage integer division.
                                                            (line  4013)
* Division by zero:                      Integer division.  (line  3871)
* Division by zero <1>:                  Integer division.  (line  3998)
* division rounding:                     core-idef.         (line 16972)
* division with potentially negative operands: Arithmetic.  (line  3780)
* dlshift:                               Bitwise operations.
                                                            (line  4153)
* dmax:                                  Double precision.  (line  3857)
* dmin:                                  Double precision.  (line  3855)
* dnegate:                               Double precision.  (line  3851)
* DO:                                    Counted Loops.     (line  6025)
* DO loops:                              Counted Loops.     (line  5813)
* doabicode,:                            Threading Words.   (line 16428)
* doabicode::                            Threading Words.   (line 16481)
* docol,:                                Threading Words.   (line 16407)
* docol::                                Threading Words.   (line 16457)
* docon,:                                Threading Words.   (line 16410)
* docon::                                Threading Words.   (line 16460)
* dodefer,:                              Threading Words.   (line 16419)
* dodefer::                              Threading Words.   (line 16469)
* dodoes routine:                        DOES>.             (line 18648)
* dodoes::                               Threading Words.   (line 16478)
* does-code!:                            Threading Words.   (line 16501)
* DOES>:                                 CREATE..DOES> details.
                                                            (line  7332)
* DOES> implementation:                  DOES>.             (line 18648)
* DOES> in a separate definition:        CREATE..DOES> details.
                                                            (line  7334)
* DOES> in interpretation state:         CREATE..DOES> details.
                                                            (line  7369)
* DOES> of non-CREATEd words:            core-ambcond.      (line 17179)
* does> tutorial:                        Defining Words Tutorial.
                                                            (line  2417)
* DOES>, visibility of current definition: core-idef.       (line 16992)
* does>-code:                            Threading Words.   (line 16484)
* DOES>-code:                            DOES>.             (line 18648)
* DOES>-parts, stack effect:             User-defined defining words using CREATE.
                                                            (line  7277)
* dofield,:                              Threading Words.   (line 16422)
* dofield::                              Threading Words.   (line 16472)
* DONE:                                  Counted Loops.     (line  6066)
* double precision arithmetic words:     Double precision.  (line  3828)
* double words, ambiguous conditions:    double-ambcond.    (line 17269)
* double words, system documentation:    The optional Double Number word set.
                                                            (line 17266)
* double%:                               Structure Glossary.
                                                            (line 12421)
* double-cell numbers, input format:     Literals in source code.
                                                            (line  3477)
* doubly indirect threaded code:         gforthmi.          (line 18176)
* douser,:                               Threading Words.   (line 16416)
* douser::                               Threading Words.   (line 16466)
* dovalue,:                              Threading Words.   (line 16425)
* dovalue::                              Threading Words.   (line 16475)
* dovar,:                                Threading Words.   (line 16413)
* dovar::                                Threading Words.   (line 16463)
* dpl:                                   Number Conversion. (line  8868)
* draw:                                  widget methods.    (line 19142)
* draw-init:                             widget methods.    (line 19139)
* drol:                                  Bitwise operations.
                                                            (line  4220)
* drop:                                  Data stack.        (line  4520)
* dror:                                  Bitwise operations.
                                                            (line  4223)
* drshift:                               Bitwise operations.
                                                            (line  4156)
* du/mod:                                Integer division.  (line  3953)
* du<:                                   Numeric comparison.
                                                            (line  4297)
* du<=:                                  Numeric comparison.
                                                            (line  4299)
* du>:                                   Numeric comparison.
                                                            (line  4301)
* du>=:                                  Numeric comparison.
                                                            (line  4303)
* dump:                                  Examining data.    (line 14280)
* dup:                                   Data stack.        (line  4524)
* duration of a system clock tick:       facility-idef.     (line 17301)
* dynamic allocation of memory:          Heap Allocation.   (line  4798)
* Dynamic superinstructions with replication: Dynamic Superinstructions.
                                                            (line 18537)
* Dynamically linked libraries in C interface: Declaring OS-level libraries.
                                                            (line 15173)
* D^:                                    Locals definition words.
                                                            (line 11634)
* early:                                 Class Declaration. (line 13459)
* early binding:                         Class Binding.     (line 12762)
* edit:                                  Locating source code definitions.
                                                            (line 14033)
* edit-line:                             Line input and conversion.
                                                            (line 11074)
* editing in ACCEPT and EXPECT:          core-idef.         (line 16823)
* eforth performance:                    Performance.       (line 18819)
* ekey:                                  Single-key input.  (line 10915)
* EKEY, encoding of keyboard events:     facility-idef.     (line 17294)
* ekey>char:                             Single-key input.  (line 10921)
* ekey>fkey:                             Single-key input.  (line 10926)
* ekey>xchar:                            Single-key input.  (line 10918)
* ekey?:                                 Single-key input.  (line 10930)
* ekeyed:                                actor methods.     (line 19052)
* elements of a Forth system:            Review - elements of a Forth system.
                                                            (line  3380)
* ELSE:                                  Arbitrary control structures.
                                                            (line  6268)
* Emacs and Gforth:                      Emacs and Gforth.  (line 17807)
* emit:                                  Displaying characters and strings.
                                                            (line 10789)
* EMIT and non-graphic characters:       core-idef.         (line 16819)
* emit-file:                             General files.     (line  9962)
* empty-buffer:                          Blocks.            (line 10351)
* empty-buffers:                         Blocks.            (line 10347)
* end-c-library:                         Defining library interfaces.
                                                            (line 15167)
* end-class:                             Objects Glossary.  (line 13150)
* end-class <1>:                         Basic Mini-OOF Usage.
                                                            (line 13509)
* end-class usage:                       Basic Objects Usage.
                                                            (line 12659)
* end-class-noname:                      Objects Glossary.  (line 13154)
* end-code:                              Assembler Definitions.
                                                            (line 15421)
* end-interface:                         Objects Glossary.  (line 13157)
* end-interface usage:                   Object Interfaces. (line 12958)
* end-interface-noname:                  Objects Glossary.  (line 13161)
* end-methods:                           Objects Glossary.  (line 13164)
* end-struct:                            Structure Glossary.
                                                            (line 12423)
* end-struct usage:                      Structure Usage.   (line 12260)
* end-structure:                         Forth200x Structures.
                                                            (line 12488)
* endcase:                               Arbitrary control structures.
                                                            (line  6300)
* ENDIF:                                 Arbitrary control structures.
                                                            (line  6285)
* endless loop:                          Simple Loops.      (line  5804)
* endof:                                 Arbitrary control structures.
                                                            (line  6317)
* endscope:                              Where are locals visible by name?.
                                                            (line 11676)
* endtry:                                Exception Handling.
                                                            (line  6547)
* endtry-iferror:                        Exception Handling.
                                                            (line  6626)
* engine:                                Engine.            (line 18361)
* engine performance:                    Performance.       (line 18803)
* engine portability:                    Portability.       (line 18375)
* engine.s:                              Produced code.     (line 18795)
* engines, gforth vs. gforth-fast vs. gforth-itc: Direct or Indirect Threaded?.
                                                            (line 18521)
* entered:                               actor methods.     (line 19064)
* environment:                           Environmental Queries.
                                                            (line  9749)
* environment variable input format:     Literals in source code.
                                                            (line  3557)
* environment variables:                 Environment variables.
                                                            (line   783)
* environment variables <1>:             gforthmi.          (line 18176)
* environment wordset:                   Notation.          (line  3622)
* environment-wordlist:                  Environmental Queries.
                                                            (line  9745)
* environment?:                          Environmental Queries.
                                                            (line  9598)
* ENVIRONMENT? string length, maximum:   core-idef.         (line 16900)
* environmental queries:                 Environmental Queries.
                                                            (line  9593)
* environmental restrictions:            Standard conformance.
                                                            (line 16786)
* equality of floats:                    Floating Point.    (line  4443)
* erase:                                 Memory Blocks.     (line  5221)
* error messages:                        Error messages.    (line 16603)
* error output, finding the source location in Emacs: Emacs and Gforth.
                                                            (line 17822)
* error-color:                           Terminal output.   (line 10832)
* error-hl-inv:                          Terminal output.   (line 10835)
* error-hl-ul:                           Terminal output.   (line 10838)
* etags.fs:                              Emacs Tags.        (line 17858)
* evaluate:                              Input Sources.     (line  8824)
* event-loop:                            Message queues.    (line 14856)
* examining data and code:               Examining data.    (line 14229)
* exception:                             Exception Handling.
                                                            (line  6450)
* exception abort sequence of ABORT":    core-idef.         (line 16881)
* exception source code:                 Locating exception source.
                                                            (line 14101)
* exception when including source:       file-idef.         (line 17352)
* exception words, implementation-defined options: exception-idef.
                                                            (line 17278)
* exception words, system documentation: The optional Exception word set.
                                                            (line 17275)
* exceptions:                            Exception Handling.
                                                            (line  6421)
* exceptions <1>:                        Exception Handling.
                                                            (line  6460)
* exceptions tutorial:                   Exceptions Tutorial.
                                                            (line  2358)
* executable image file:                 Running Image Files.
                                                            (line 18230)
* execute:                               Execution token.   (line  8165)
* execute-exit:                          Execution token.   (line  8168)
* execute-parsing:                       The Input Stream.  (line  9307)
* execute-parsing-file:                  The Input Stream.  (line  9323)
* execute-task:                          Basic multi-tasking.
                                                            (line 14689)
* executing code on startup:             Invoking Gforth.   (line   650)
* execution frequency:                   Code Coverage.     (line 14546)
* execution semantics:                   Interpretation and Compilation Semantics.
                                                            (line  7962)
* execution token:                       Introducing the Text Interpreter.
                                                            (line  2838)
* execution token <1>:                   Execution token.   (line  8088)
* execution token input format:          Literals in source code.
                                                            (line  3563)
* execution token of last defined word:  Anonymous Definitions.
                                                            (line  7026)
* execution token of words with undefined execution semantics: core-ambcond.
                                                            (line 17015)
* execution tokens tutorial:             Execution Tokens Tutorial.
                                                            (line  2272)
* exercises:                             Exercises.         (line  3449)
* EXIT:                                  Calls and returns. (line  6406)
* exit in m: ... ;m:                     Method conveniences.
                                                            (line 12819)
* exitm:                                 Objects Glossary.  (line 13168)
* exitm discussion:                      Method conveniences.
                                                            (line 12819)
* expand-where:                          Locating uses of a word.
                                                            (line 14084)
* expect:                                Line input and conversion.
                                                            (line 11120)
* EXPECT, display after end of input:    core-idef.         (line 16877)
* EXPECT, editing:                       core-idef.         (line 16823)
* explicit register declarations:        Portability.       (line 18409)
* exponent too big for conversion (DF!, DF@, SF!, SF@): floating-ambcond.
                                                            (line 17480)
* extend-mem:                            Heap Allocation.   (line  4838)
* extend-structure:                      Forth200x Structures.
                                                            (line 12484)
* extended records:                      Structure Usage.   (line 12305)
* f!:                                    Memory Access.     (line  4899)
* f! used with an address that is not float aligned: floating-ambcond.
                                                            (line 17445)
* f*:                                    Floating Point.    (line  4340)
* f**:                                   Floating Point.    (line  4365)
* f+:                                    Floating Point.    (line  4336)
* f,:                                    Dictionary allocation.
                                                            (line  4734)
* f, stack item type:                    Notation.          (line  3663)
* f-:                                    Floating Point.    (line  4338)
* f-rot:                                 Floating point stack.
                                                            (line  4587)
* f.:                                    Floating-point output.
                                                            (line 10614)
* f.rdp:                                 Floating-point output.
                                                            (line 10650)
* f.s:                                   Examining data.    (line 14239)
* f.s-precision:                         Examining data.    (line 14244)
* f/:                                    Floating Point.    (line  4342)
* f0<:                                   Floating Point.    (line  4471)
* f0<=:                                  Floating Point.    (line  4473)
* f0<>:                                  Floating Point.    (line  4475)
* f0=:                                   Floating Point.    (line  4477)
* f0>:                                   Floating Point.    (line  4479)
* f0>=:                                  Floating Point.    (line  4481)
* f2*:                                   Floating Point.    (line  4386)
* f2/:                                   Floating Point.    (line  4389)
* f83name, stack item type:              Notation.          (line  3696)
* F::                                    Locals definition words.
                                                            (line 11646)
* f<:                                    Floating Point.    (line  4463)
* f<=:                                   Floating Point.    (line  4465)
* f<>:                                   Floating Point.    (line  4461)
* f=:                                    Floating Point.    (line  4459)
* f>:                                    Floating Point.    (line  4467)
* f>=:                                   Floating Point.    (line  4469)
* f>buf-rdp:                             Floating-point output.
                                                            (line 10695)
* f>d:                                   Floating Point.    (line  4332)
* F>D, integer part of float cannot be represented by d: floating-ambcond.
                                                            (line 17503)
* f>l:                                   Locals implementation.
                                                            (line 11944)
* f>s:                                   Floating Point.    (line  4330)
* f>str-rdp:                             Floating-point output.
                                                            (line 10689)
* f@:                                    Memory Access.     (line  4896)
* f@ used with an address that is not float aligned: floating-ambcond.
                                                            (line 17445)
* f@localn:                              Locals implementation.
                                                            (line 11934)
* FA::                                   Locals definition words.
                                                            (line 11649)
* fabs:                                  Floating Point.    (line  4346)
* facility words, ambiguous conditions:  facility-ambcond.  (line 17314)
* facility words, implementation-defined options: facility-idef.
                                                            (line 17293)
* facility words, system documentation:  The optional Facility word set.
                                                            (line 17290)
* facos:                                 Floating Point.    (line  4419)
* FACOS, |float|>1:                      floating-ambcond.  (line 17500)
* facosh:                                Floating Point.    (line  4435)
* FACOSH, float<1:                       floating-ambcond.  (line 17484)
* factoring:                             Introduction.      (line  2788)
* factoring similar colon definitions:   CREATE..DOES> applications.
                                                            (line  7297)
* factoring tutorial:                    Factoring Tutorial.
                                                            (line  1378)
* fade-color::                           widget methods.    (line 19224)
* falign:                                Dictionary allocation.
                                                            (line  4776)
* faligned:                              Address arithmetic.
                                                            (line  5111)
* falog:                                 Floating Point.    (line  4383)
* false:                                 Boolean Flags.     (line  3765)
* fam (file access method):              General files.     (line  9897)
* fasin:                                 Floating Point.    (line  4417)
* FASIN, |float|>1:                      floating-ambcond.  (line 17500)
* fasinh:                                Floating Point.    (line  4433)
* FASINH, float<0:                       floating-ambcond.  (line 17495)
* fast-throw:                            Exception Handling.
                                                            (line  6430)
* fatan:                                 Floating Point.    (line  4421)
* fatan2:                                Floating Point.    (line  4423)
* FATAN2, both arguments are equal to zero: floating-ambcond.
                                                            (line 17463)
* fatanh:                                Floating Point.    (line  4437)
* FATANH, |float|>1:                     floating-ambcond.  (line 17500)
* faxpy:                                 Floating Point.    (line  4402)
* fclearstack:                           Examining data.    (line 14269)
* fconstant:                             Constants.         (line  6822)
* fcopysign:                             Floating Point.    (line  4348)
* fcos:                                  Floating Point.    (line  4410)
* fcosh:                                 Floating Point.    (line  4429)
* fdepth:                                Examining data.    (line 14262)
* FDL, GNU Free Documentation License:   GNU Free Documentation License.
                                                            (line 19410)
* fdrop:                                 Floating point stack.
                                                            (line  4566)
* fdup:                                  Floating point stack.
                                                            (line  4570)
* fe.:                                   Floating-point output.
                                                            (line 10618)
* fexp:                                  Floating Point.    (line  4370)
* fexpm1:                                Floating Point.    (line  4372)
* ffield::                               Forth200x Structures.
                                                            (line 12504)
* ffourth:                               Floating point stack.
                                                            (line  4576)
* field:                                 Structure Glossary.
                                                            (line 12428)
* field naming convention:               Structure Naming Convention.
                                                            (line 12352)
* field usage:                           Structure Usage.   (line 12260)
* field usage in class definition:       Basic Objects Usage.
                                                            (line 12680)
* field::                                Forth200x Structures.
                                                            (line 12498)
* file access methods used:              file-idef.         (line 17326)
* file exceptions:                       file-idef.         (line 17333)
* file input nesting, maximum depth:     file-idef.         (line 17361)
* file line terminator:                  file-idef.         (line 17337)
* file name format:                      file-idef.         (line 17342)
* file search path:                      Search Paths.      (line 10090)
* file words, ambiguous conditions:      file-ambcond.      (line 17381)
* file words, implementation-defined options: file-idef.    (line 17325)
* file words, system documentation:      The optional File-Access word set.
                                                            (line 17322)
* file-eof?:                             General files.     (line  9955)
* file-handling:                         General files.     (line  9894)
* file-position:                         General files.     (line  9968)
* file-size:                             General files.     (line  9972)
* file-status:                           General files.     (line  9966)
* FILE-STATUS, returned information:     file-idef.         (line 17346)
* file>fpath:                            Source Search Paths.
                                                            (line 10133)
* file>path:                             General Search Paths.
                                                            (line 10158)
* filename-match:                        Directories.       (line 10067)
* filenames in assertion output:         Assertions.        (line 14469)
* filenames in ~~ output:                Debugging.         (line 14360)
* files:                                 Files.             (line  9804)
* files containing blocks:               file-idef.         (line 17368)
* files containing Forth code, tutorial: Using files for Forth code Tutorial.
                                                            (line  1138)
* files tutorial:                        Files Tutorial.    (line  2095)
* fill:                                  Memory Blocks.     (line  5218)
* find:                                  Word Lists.        (line  9424)
* find-name:                             Name token.        (line  8205)
* find-name-in:                          Name token.        (line  8209)
* first definition:                      Your first definition.
                                                            (line  3090)
* first field optimization:              Structure Usage.   (line 12325)
* first field optimization, implementation: Structure Implementation.
                                                            (line 12386)
* fkey.:                                 Single-key input.  (line 11049)
* flags on the command line:             Invoking Gforth.   (line   473)
* flags tutorial:                        Flags and Comparisons Tutorial.
                                                            (line  1530)
* flavours of locals:                    Gforth locals.     (line 11509)
* FLiteral:                              Literals.          (line  8399)
* fln:                                   Floating Point.    (line  4375)
* FLN, float<=0:                         floating-ambcond.  (line 17491)
* flnp1:                                 Floating Point.    (line  4377)
* FLNP1, float<=-1:                      floating-ambcond.  (line 17487)
* float:                                 Address arithmetic.
                                                            (line  5105)
* float%:                                Structure Glossary.
                                                            (line 12435)
* float+:                                Address arithmetic.
                                                            (line  5102)
* float/:                                Address arithmetic.
                                                            (line  5109)
* floating point arithmetic words:       Floating Point.    (line  4308)
* floating point numbers, format and range: floating-idef.  (line 17416)
* floating point tutorial:               Floating Point Tutorial.
                                                            (line  2023)
* floating point unidentified fault, integer division: core-ambcond.
                                                            (line 17027)
* floating-point arithmetic, pitfalls:   Floating Point.    (line  4314)
* floating-point comparisons:            Floating Point.    (line  4443)
* floating-point constants:              Floating Point.    (line  4483)
* floating-point dividing by zero:       floating-ambcond.  (line 17475)
* floating-point numbers, input format:  Literals in source code.
                                                            (line  3500)
* floating-point numbers, rounding or truncation: floating-idef.
                                                            (line 17423)
* floating-point output:                 Floating-point output.
                                                            (line 10612)
* floating-point result out of range:    floating-ambcond.  (line 17449)
* floating-point stack:                  Stack Manipulation.
                                                            (line  4510)
* floating-point stack in the standard:  Stack Manipulation.
                                                            (line  4505)
* floating-point stack manipulation words: Floating point stack.
                                                            (line  4566)
* floating-point stack size:             floating-idef.     (line 17429)
* floating-point stack width:            floating-idef.     (line 17435)
* Floating-point unidentified fault:     Integer division.  (line  3871)
* Floating-point unidentified fault (on integer division): Integer division.
                                                            (line  3998)
* floating-point unidentified fault, F>D: floating-ambcond. (line 17503)
* floating-point unidentified fault, FACOS, FASIN or FATANH: floating-ambcond.
                                                            (line 17500)
* floating-point unidentified fault, FACOSH: floating-ambcond.
                                                            (line 17484)
* floating-point unidentified fault, FASINH or FSQRT: floating-ambcond.
                                                            (line 17495)
* floating-point unidentified fault, FLN or FLOG: floating-ambcond.
                                                            (line 17491)
* floating-point unidentified fault, FLNP1: floating-ambcond.
                                                            (line 17487)
* floating-point unidentified fault, FP divide-by-zero: floating-ambcond.
                                                            (line 17475)
* floating-point words, ambiguous conditions: floating-ambcond.
                                                            (line 17440)
* floating-point words, implementation-defined options: floating-idef.
                                                            (line 17415)
* floating-point words, system documentation: The optional Floating-Point word set.
                                                            (line 17412)
* floating-stack:                        Environmental Queries.
                                                            (line  9656)
* floats:                                Address arithmetic.
                                                            (line  5099)
* flog:                                  Floating Point.    (line  4380)
* FLOG, float<=0:                        floating-ambcond.  (line 17491)
* floor:                                 Floating Point.    (line  4355)
* FLOORED:                               Environmental Queries.
                                                            (line  9635)
* floored division:                      Integer division.  (line  3876)
* flush:                                 Blocks.            (line 10366)
* flush-file:                            General files.     (line  9964)
* flush-icache:                          Assembler Definitions.
                                                            (line 15438)
* fm/mod:                                Integer division.  (line  3944)
* fmax:                                  Floating Point.    (line  4351)
* fmin:                                  Floating Point.    (line  4353)
* fnegate:                               Floating Point.    (line  4344)
* fnip:                                  Floating point stack.
                                                            (line  4568)
* focus:                                 actor methods.     (line 19058)
* FOR:                                   Counted Loops.     (line  6028)
* FOR loops:                             Counted Loops.     (line  5970)
* foreign language interface:            C Interface.       (line 14916)
* FORGET, deleting the compilation word list: programming-ambcond.
                                                            (line 17573)
* FORGET, name can't be found:           programming-ambcond.
                                                            (line 17582)
* FORGET, removing a needed definition:  programming-ambcond.
                                                            (line 17599)
* forgeting words:                       Forgetting words.  (line 14289)
* FORK:                                  Regular Expressions.
                                                            (line 13796)
* form:                                  Terminal output.   (line 10812)
* format and range of floating point numbers: floating-idef.
                                                            (line 17416)
* format of glossary entries:            Notation.          (line  3587)
* formatted numeric output:              Formatted numeric output.
                                                            (line 10461)
* Forth:                                 Word Lists.        (line  9405)
* Forth - an introduction:               Introduction.      (line  2764)
* Forth mode in Emacs:                   Emacs and Gforth.  (line 17807)
* Forth source files:                    Forth source files.
                                                            (line  9815)
* Forth Tutorial:                        Tutorial.          (line   947)
* forth-recognize:                       Dealing with existing Recognizers.
                                                            (line  9176)
* forth-recognizer:                      Dealing with existing Recognizers.
                                                            (line  9179)
* Forth-related information:             Forth-related information.
                                                            (line 19394)
* forth-wordlist:                        Word Lists.        (line  9353)
* forth.el:                              Emacs and Gforth.  (line 17807)
* forward:                               Forward.           (line  7893)
* fourth:                                Data stack.        (line  4530)
* fover:                                 Floating point stack.
                                                            (line  4572)
* FP output:                             Floating-point output.
                                                            (line 10612)
* FP tutorial:                           Floating Point Tutorial.
                                                            (line  2023)
* fp!:                                   Stack pointer manipulation.
                                                            (line  4640)
* fp.:                                   Floating-point output.
                                                            (line 10626)
* fp0:                                   Stack pointer manipulation.
                                                            (line  4635)
* fp@:                                   Stack pointer manipulation.
                                                            (line  4638)
* fpath:                                 Source Search Paths.
                                                            (line 10128)
* fpick:                                 Floating point stack.
                                                            (line  4582)
* free:                                  Heap Allocation.   (line  4815)
* free-closure:                          Closures.          (line 12093)
* free-mem-var:                          Heap Allocation.   (line  4834)
* frequently asked questions:            Forth-related information.
                                                            (line 19394)
* frot:                                  Floating point stack.
                                                            (line  4585)
* fround:                                Floating Point.    (line  4359)
* fs.:                                   Floating-point output.
                                                            (line 10622)
* fsin:                                  Floating Point.    (line  4408)
* fsincos:                               Floating Point.    (line  4412)
* fsinh:                                 Floating Point.    (line  4427)
* fsqrt:                                 Floating Point.    (line  4368)
* FSQRT, float<0:                        floating-ambcond.  (line 17495)
* fswap:                                 Floating point stack.
                                                            (line  4580)
* ftan:                                  Floating Point.    (line  4415)
* FTAN on an argument r1 where cos(r1) is zero: floating-ambcond.
                                                            (line 17467)
* ftanh:                                 Floating Point.    (line  4431)
* fthird:                                Floating point stack.
                                                            (line  4574)
* ftrunc:                                Floating Point.    (line  4362)
* ftuck:                                 Floating point stack.
                                                            (line  4578)
* fully relocatable image files:         Fully Relocatable Image Files.
                                                            (line 18125)
* functions, tutorial:                   Colon Definitions Tutorial.
                                                            (line  1206)
* fvalue:                                Values.            (line  6889)
* fvariable:                             Variables.         (line  6781)
* fvarue:                                Varues.            (line  6915)
* F^:                                    Locals definition words.
                                                            (line 11652)
* f_, stack item type:                   Notation.          (line  3684)
* f~:                                    Floating Point.    (line  4455)
* f~abs:                                 Floating Point.    (line  4452)
* f~rel:                                 Floating Point.    (line  4449)
* g:                                     Locating source code definitions.
                                                            (line 14017)
* gap:                                   widget methods.    (line 19112)
* gdb disassembler:                      Common Disassembler.
                                                            (line 15568)
* general control structures (case):     General control structures with CASE.
                                                            (line  6140)
* general files:                         General files.     (line  9894)
* get:                                   actor methods.     (line 19076)
* get-block-fid:                         Blocks.            (line 10316)
* get-current:                           Word Lists.        (line  9362)
* get-dir:                               Directories.       (line 10072)
* get-order:                             Word Lists.        (line  9368)
* get-recognizers:                       Dealing with existing Recognizers.
                                                            (line  9163)
* getenv:                                Passing Commands to the OS.
                                                            (line 16549)
* gforth:                                Environmental Queries.
                                                            (line  9722)
* GFORTH -- environment variable:         Environment variables.
                                                            (line   811)
* GFORTH -- environment variable <1>:     gforthmi.          (line 18176)
* Gforth - leaving:                      Leaving Gforth.    (line   694)
* gforth engine:                         Direct or Indirect Threaded?.
                                                            (line 18521)
* Gforth environment:                    Gforth Environment.
                                                            (line   464)
* Gforth extensions:                     Standard vs Extensions.
                                                            (line 17633)
* Gforth files:                          Gforth Files.      (line   824)
* Gforth locals:                         Gforth locals.     (line 11473)
* Gforth performance:                    Performance.       (line 18803)
* Gforth stability:                      Stability Goals.   (line   439)
* gforth-ditc:                           gforthmi.          (line 18176)
* gforth-fast and backtraces:            Error messages.    (line 16650)
* gforth-fast engine:                    Direct or Indirect Threaded?.
                                                            (line 18521)
* gforth-fast, difference from gforth:   Error messages.    (line 16650)
* gforth-itc engine:                     Direct or Indirect Threaded?.
                                                            (line 18525)
* gforth.el:                             Emacs and Gforth.  (line 17807)
* gforth.el, installation:               Installing gforth.el.
                                                            (line 17838)
* gforth.fi, relocatability:             Fully Relocatable Image Files.
                                                            (line 18125)
* GFORTHD -- environment variable:        Environment variables.
                                                            (line   813)
* GFORTHD -- environment variable <1>:    gforthmi.          (line 18176)
* GFORTHHIST -- environment variable:     Environment variables.
                                                            (line   785)
* gforthmi:                              gforthmi.          (line 18138)
* GFORTHPATH -- environment variable:     Environment variables.
                                                            (line   789)
* GFORTHSYSTEMPREFIX -- environment variable: Environment variables.
                                                            (line   805)
* gg:                                    Locating uses of a word.
                                                            (line 14066)
* giving a name to a library interface:  Defining library interfaces.
                                                            (line 15119)
* glossary notation format:              Notation.          (line  3587)
* GNU C for the engine:                  Portability.       (line 18392)
* goals of the Gforth project:           Goals.             (line   402)
* h:                                     widget methods.    (line 19106)
* halt:                                  Basic multi-tasking.
                                                            (line 14705)
* header fields:                         Header fields.     (line 16126)
* header methods:                        Header methods.    (line 16196)
* header space:                          Word Lists.        (line  9330)
* heap allocation:                       Heap Allocation.   (line  4798)
* heap-new:                              Objects Glossary.  (line 13171)
* heap-new discussion:                   Creating objects.  (line 12728)
* heap-new usage:                        Basic Objects Usage.
                                                            (line 12702)
* help:                                  Help on Gforth.    (line   705)
* help <1>:                              Help on Gforth.    (line   707)
* here:                                  Dictionary allocation.
                                                            (line  4714)
* hex:                                   Number Conversion. (line  8860)
* hglue:                                 widget methods.    (line 19151)
* hglue@:                                widget methods.    (line 19160)
* hide:                                  actor methods.     (line 19073)
* highlighting Forth code in Emacs:      Hilighting.        (line 17873)
* hilighting Forth code in Emacs:        Hilighting.        (line 17873)
* history file:                          Command-line editing.
                                                            (line   760)
* hmcopy,:                               Threading Words.   (line 16403)
* hold:                                  Formatted numeric output.
                                                            (line 10517)
* holds:                                 Formatted numeric output.
                                                            (line 10521)
* hooks in the text interpreter:         Text Interpreter Hooks.
                                                            (line  9230)
* how::                                  Class Declaration. (line 13472)
* hybrid direct/indirect threaded code:  Direct or Indirect Threaded?.
                                                            (line 18513)
* i:                                     Counted Loops.     (line  6043)
* i':                                    Counted Loops.     (line  6052)
* I/O - blocks:                          Blocks.            (line 10191)
* I/O - file-handling:                   Files.             (line  9804)
* I/O - keyboard and display:            Other I/O.         (line 10409)
* I/O - see input:                       Line input and conversion.
                                                            (line 11062)
* I/O exception in block transfer:       block-ambcond.     (line 17239)
* id.:                                   Name token.        (line  8250)
* IDE (integrated development environment): Locating source code definitions.
                                                            (line 13976)
* IF:                                    Arbitrary control structures.
                                                            (line  6226)
* IF control structure:                  Selection.         (line  5698)
* if, tutorial:                          Conditional execution Tutorial.
                                                            (line  1484)
* iferror:                               Exception Handling.
                                                            (line  6550)
* image file:                            Image Files.       (line 17975)
* image file background:                 Image File Background.
                                                            (line 18003)
* image file initialization sequence:    Modifying the Startup Sequence.
                                                            (line 18303)
* image file invocation:                 Running Image Files.
                                                            (line 18226)
* image file loader:                     Image File Background.
                                                            (line 18038)
* image file, data-relocatable:          Data-Relocatable Image Files.
                                                            (line 18108)
* image file, executable:                Running Image Files.
                                                            (line 18230)
* image file, fully relocatable:         Fully Relocatable Image Files.
                                                            (line 18125)
* image file, non-relocatable:           Non-Relocatable Image Files.
                                                            (line 18089)
* image file, stack and dictionary sizes: Stack and Dictionary Sizes.
                                                            (line 18205)
* image file, turnkey applications:      Modifying the Startup Sequence.
                                                            (line 18319)
* image license:                         Image Licensing Issues.
                                                            (line 17982)
* immediate:                             Interpretation and Compilation Semantics.
                                                            (line  7987)
* immediate words:                       How does that work?.
                                                            (line  3255)
* immediate words <1>:                   Interpretation and Compilation Semantics.
                                                            (line  7985)
* immediate, tutorial:                   Interpretation and Compilation Semantics and Immediacy Tutorial.
                                                            (line  2199)
* immediate?:                            Header methods.    (line 16359)
* implementation:                        Objects Glossary.  (line 13174)
* implementation of locals:              Locals implementation.
                                                            (line 11924)
* implementation of structures:          Structure Implementation.
                                                            (line 12368)
* implementation usage:                  Object Interfaces. (line 12958)
* implementation-defined options, block words: block-idef.  (line 17223)
* implementation-defined options, core words: core-idef.    (line 16812)
* implementation-defined options, exception words: exception-idef.
                                                            (line 17278)
* implementation-defined options, facility words: facility-idef.
                                                            (line 17293)
* implementation-defined options, file words: file-idef.    (line 17325)
* implementation-defined options, floating-point words: floating-idef.
                                                            (line 17415)
* implementation-defined options, locals words: locals-idef.
                                                            (line 17517)
* implementation-defined options, memory-allocation words: memory-idef.
                                                            (line 17540)
* implementation-defined options, programming-tools words: programming-idef.
                                                            (line 17552)
* implementation-defined options, search-order words: search-idef.
                                                            (line 17607)
* in-lining of constants:                Constants.         (line  6837)
* include:                               Forth source files.
                                                            (line  9855)
* include search path:                   Search Paths.      (line 10090)
* include, placement in files:           Emacs Tags.        (line 17858)
* include-file:                          Forth source files.
                                                            (line  9841)
* INCLUDE-FILE, file-id is invalid:      file-ambcond.      (line 17390)
* INCLUDE-FILE, I/O exception reading or closing file-id: file-ambcond.
                                                            (line 17394)
* include-locale:                        i18n and l10n.     (line 11324)
* included:                              Forth source files.
                                                            (line  9845)
* INCLUDED, I/O exception reading or closing file-id: file-ambcond.
                                                            (line 17394)
* INCLUDED, named file cannot be opened: file-ambcond.      (line 17398)
* included-locale:                       i18n and l10n.     (line 11321)
* included?:                             Forth source files.
                                                            (line  9848)
* including files:                       Forth source files.
                                                            (line  9815)
* including files, stack effect:         Forth source files.
                                                            (line  9829)
* indentation of Forth code in Emacs:    Auto-Indentation.  (line 17911)
* indirect threaded inner interpreter:   Threading.         (line 18429)
* infile-execute:                        Redirection.       (line 10017)
* infile-id:                             Redirection.       (line 10020)
* infinity:                              Floating Point.    (line  4487)
* info-color:                            Terminal output.   (line 10844)
* inheritance:                           Object-Oriented Terminology.
                                                            (line 12597)
* init-asm:                              Assembler Definitions.
                                                            (line 15399)
* init-buffer:                           Heap Allocation.   (line  4854)
* init-object:                           Objects Glossary.  (line 13178)
* init-object discussion:                Creating objects.  (line 12734)
* initialization of locals:              Gforth locals.     (line 11557)
* initialization sequence of image file: Modifying the Startup Sequence.
                                                            (line 18303)
* initiate:                              Basic multi-tasking.
                                                            (line 14664)
* inline::                               Colon Definitions. (line  6944)
* inner interpreter implementation:      Threading.         (line 18423)
* inner interpreter optimization:        Scheduling.        (line 18450)
* inner interpreter, direct threaded:    Threading.         (line 18440)
* inner interpreter, indirect threaded:  Threading.         (line 18429)
* input buffer:                          The Text Interpreter.
                                                            (line  8650)
* input format for body-relative addresses: Literals in source code.
                                                            (line  3572)
* input format for characters/code points: Literals in source code.
                                                            (line  3493)
* input format for double-cell numbers:  Literals in source code.
                                                            (line  3477)
* input format for environment variables: Literals in source code.
                                                            (line  3557)
* input format for execution tokens:     Literals in source code.
                                                            (line  3563)
* input format for floating-point numbers: Literals in source code.
                                                            (line  3500)
* input format for name tokens:          Literals in source code.
                                                            (line  3569)
* input format for single-cell numbers:  Literals in source code.
                                                            (line  3456)
* input format for strings:              Literals in source code.
                                                            (line  3547)
* input from pipes:                      Gforth in pipes.   (line   845)
* input line size, maximum:              file-idef.         (line 17365)
* input line terminator:                 core-idef.         (line 16885)
* Input Redirection:                     Redirection.       (line  9994)
* input sources:                         Input Sources.     (line  8789)
* input stream:                          The Input Stream.  (line  9242)
* input, linewise from terminal:         Line input and conversion.
                                                            (line 11062)
* input, single-key:                     Single-key input.  (line 10877)
* input-color:                           Terminal output.   (line 10850)
* insert:                                Memory Blocks.     (line  5227)
* inst-value:                            Objects Glossary.  (line 13182)
* inst-value usage:                      Method conveniences.
                                                            (line 12848)
* inst-value visibility:                 Classes and Scoping.
                                                            (line 12881)
* inst-var:                              Objects Glossary.  (line 13186)
* inst-var implementation:               Objects Implementation.
                                                            (line 13032)
* inst-var usage:                        Method conveniences.
                                                            (line 12826)
* inst-var visibility:                   Classes and Scoping.
                                                            (line 12881)
* instance variables:                    Object-Oriented Terminology.
                                                            (line 12571)
* instruction pointer:                   Threading.         (line 18433)
* insufficient data stack or return stack space: core-ambcond.
                                                            (line 17032)
* insufficient space for loop control parameters: core-ambcond.
                                                            (line 17045)
* insufficient space in the dictionary:  core-ambcond.      (line 17048)
* INT-[I]:                               Interpreter Directives.
                                                            (line  8979)
* integer types, ranges:                 core-idef.         (line 16925)
* integrated development environment:    Locating source code definitions.
                                                            (line 13976)
* interface:                             Objects Glossary.  (line 13190)
* interface implementation:              Objects Implementation.
                                                            (line 13043)
* interface to C functions:              C Interface.       (line 14916)
* interface usage:                       Object Interfaces. (line 12958)
* interfaces for objects:                Object Interfaces. (line 12937)
* interpret:                             The Text Interpreter.
                                                            (line  8766)
* interpret state:                       The Text Interpreter.
                                                            (line  8641)
* Interpret/Compile states:              Interpret/Compile states.
                                                            (line  8893)
* interpret/compile::                    Combined words.    (line  8020)
* interpretation semantics:              How does that work?.
                                                            (line  3227)
* interpretation semantics <1>:          Interpretation and Compilation Semantics.
                                                            (line  7945)
* interpretation semantics tutorial:     Interpretation and Compilation Semantics and Immediacy Tutorial.
                                                            (line  2199)
* interpreter - outer:                   The Text Interpreter.
                                                            (line  8636)
* interpreter directives:                Interpreter Directives.
                                                            (line  8907)
* Interpreting a compile-only word:      core-ambcond.      (line 17055)
* Interpreting a compile-only word, for a local: locals-ambcond.
                                                            (line 17527)
* interpreting a word with undefined interpretation semantics: core-ambcond.
                                                            (line 17055)
* invalid block number:                  block-ambcond.     (line 17243)
* Invalid memory address:                core-ambcond.      (line 17004)
* Invalid memory address, stack overflow: core-ambcond.     (line 17032)
* Invalid name argument, TO:             core-ambcond.      (line 17152)
* Invalid name argument, TO <1>:         locals-ambcond.    (line 17532)
* invert:                                Bitwise operations.
                                                            (line  4135)
* invoking a selector:                   Object-Oriented Terminology.
                                                            (line 12585)
* invoking Gforth:                       Invoking Gforth.   (line   473)
* invoking image files:                  Running Image Files.
                                                            (line 18226)
* ior type description:                  Notation.          (line  3694)
* ior values and meaning:                file-idef.         (line 17355)
* ior values and meaning <1>:            memory-idef.       (line 17541)
* IS:                                    Deferred Words.    (line  7861)
* items on the stack after interpretation: Stack depth changes.
                                                            (line 16714)
* iterate over array:                    Counted Loops.     (line  5931)
* j:                                     Counted Loops.     (line  6046)
* JOIN:                                  Regular Expressions.
                                                            (line 13799)
* k:                                     Counted Loops.     (line  6049)
* k-alt-mask:                            Single-key input.  (line 10994)
* k-backspace:                           Single-key input.  (line 11002)
* k-ctrl-mask:                           Single-key input.  (line 10992)
* k-delete:                              Single-key input.  (line 10956)
* k-down:                                Single-key input.  (line 10941)
* k-end:                                 Single-key input.  (line 10946)
* k-enter:                               Single-key input.  (line 11000)
* k-eof:                                 Single-key input.  (line 11023)
* k-f1:                                  Single-key input.  (line 10961)
* k-f10:                                 Single-key input.  (line 10979)
* k-f11:                                 Single-key input.  (line 10981)
* k-f12:                                 Single-key input.  (line 10983)
* k-f2:                                  Single-key input.  (line 10963)
* k-f3:                                  Single-key input.  (line 10965)
* k-f4:                                  Single-key input.  (line 10967)
* k-f5:                                  Single-key input.  (line 10969)
* k-f6:                                  Single-key input.  (line 10971)
* k-f7:                                  Single-key input.  (line 10973)
* k-f8:                                  Single-key input.  (line 10975)
* k-f9:                                  Single-key input.  (line 10977)
* k-home:                                Single-key input.  (line 10943)
* k-insert:                              Single-key input.  (line 10954)
* k-left:                                Single-key input.  (line 10935)
* k-mute:                                Single-key input.  (line 11014)
* k-next:                                Single-key input.  (line 10951)
* k-pause:                               Single-key input.  (line 11012)
* k-prior:                               Single-key input.  (line 10948)
* k-right:                               Single-key input.  (line 10937)
* k-sel:                                 Single-key input.  (line 11020)
* k-shift-mask:                          Single-key input.  (line 10990)
* k-tab:                                 Single-key input.  (line 11004)
* k-up:                                  Single-key input.  (line 10939)
* k-voldown:                             Single-key input.  (line 11018)
* k-volup:                               Single-key input.  (line 11016)
* k-winch:                               Single-key input.  (line 11008)
* kern*.fi, relocatability:              Fully Relocatable Image Files.
                                                            (line 18125)
* kerning:                               widget methods.    (line 19118)
* key:                                   Single-key input.  (line 10880)
* key-file:                              General files.     (line  9942)
* key-ior:                               Single-key input.  (line 10883)
* key?:                                  Single-key input.  (line 10887)
* key?-file:                             General files.     (line  9949)
* keyboard events, encoding in EKEY:     facility-idef.     (line 17294)
* kill:                                  Basic multi-tasking.
                                                            (line 14700)
* kill-task:                             Basic multi-tasking.
                                                            (line 14697)
* Kuehling, David:                       Emacs and Gforth.  (line 17807)
* l:                                     Locating source code definitions.
                                                            (line 14006)
* l!:                                    Special Memory Accesses.
                                                            (line  4960)
* L":                                    i18n and l10n.     (line 11290)
* l,:                                    Dictionary allocation.
                                                            (line  4747)
* l>s:                                   Special Memory Accesses.
                                                            (line  5021)
* l@:                                    Special Memory Accesses.
                                                            (line  4957)
* labels as values:                      Threading.         (line 18423)
* lalign:                                Address arithmetic.
                                                            (line  5165)
* laligned:                              Address arithmetic.
                                                            (line  5162)
* LANG -- environment variable:           Environment variables.
                                                            (line   794)
* Language:                              i18n and l10n.     (line 11309)
* last word was headerless:              core-ambcond.      (line 17149)
* lastfit:                               widget methods.    (line 19148)
* late binding:                          Class Binding.     (line 12762)
* latest:                                Name token.        (line  8213)
* latestnt:                              Name token.        (line  8217)
* latestxt:                              Anonymous Definitions.
                                                            (line  7026)
* lbe:                                   Special Memory Accesses.
                                                            (line  4988)
* LC_ALL -- environment variable:         Environment variables.
                                                            (line   796)
* LC_CTYPE -- environment variable:       Environment variables.
                                                            (line   798)
* LEAVE:                                 Counted Loops.     (line  6058)
* leaving definitions, tutorial:         Leaving definitions or loops Tutorial.
                                                            (line  1771)
* leaving Gforth:                        Leaving Gforth.    (line   694)
* leaving loops, tutorial:               Leaving definitions or loops Tutorial.
                                                            (line  1771)
* left:                                  actor methods.     (line 19067)
* length of a line affected by \:        block-idef.        (line 17228)
* lfield::                               Forth200x Structures.
                                                            (line 12516)
* lib-error:                             Low-Level C Interface Words.
                                                            (line 15286)
* lib-sym:                               Low-Level C Interface Words.
                                                            (line 15284)
* Libraries in C interface:              Declaring OS-level libraries.
                                                            (line 15173)
* library interface names:               Defining library interfaces.
                                                            (line 15119)
* license:                               Help on Gforth.    (line   719)
* license for images:                    Image Licensing Issues.
                                                            (line 17982)
* lifetime of locals:                    How long do locals live?.
                                                            (line 11847)
* light-mode:                            Terminal output.   (line 10862)
* line input from terminal:              Line input and conversion.
                                                            (line 11062)
* line terminator on input:              core-idef.         (line 16885)
* line-end-hook:                         Text Interpreter Hooks.
                                                            (line  9236)
* list:                                  Blocks.            (line 10323)
* LIST display format:                   block-idef.        (line 17224)
* list-size:                             Locals implementation.
                                                            (line 12016)
* Literal:                               Literals.          (line  8380)
* literal tutorial:                      Literal Tutorial.  (line  2585)
* Literals:                              Literals.          (line  8344)
* Literals (in source code):             Literals in source code.
                                                            (line  3456)
* literals for characters and strings:   String and character literals.
                                                            (line  5304)
* little-endian:                         Special Memory Accesses.
                                                            (line  4921)
* ll:                                    Locating uses of a word.
                                                            (line 14071)
* lle:                                   Special Memory Accesses.
                                                            (line  4992)
* load:                                  Blocks.            (line 10369)
* load-cov:                              Code Coverage.     (line 14608)
* loader for image files:                Image File Background.
                                                            (line 18038)
* loading files at startup:              Invoking Gforth.   (line   650)
* loading Forth code, tutorial:          Using files for Forth code Tutorial.
                                                            (line  1138)
* local in interpretation state:         locals-ambcond.    (line 17527)
* local variables, tutorial:             Local Variables Tutorial.
                                                            (line  1449)
* locale and case-sensitivity:           core-idef.         (line 16840)
* locale!:                               i18n and l10n.     (line 11305)
* locale-csv:                            i18n and l10n.     (line 11327)
* locale-csv-out:                        i18n and l10n.     (line 11337)
* locale-file:                           i18n and l10n.     (line 11318)
* locale@:                               i18n and l10n.     (line 11302)
* locals:                                Locals.            (line 11458)
* locals and return stack:               Return stack.      (line  4592)
* locals flavours:                       Gforth locals.     (line 11509)
* locals implementation:                 Locals implementation.
                                                            (line 11924)
* locals information on the control-flow stack: Locals implementation.
                                                            (line 12002)
* locals initialization:                 Gforth locals.     (line 11557)
* locals lifetime:                       How long do locals live?.
                                                            (line 11847)
* locals programming style:              Locals programming style.
                                                            (line 11861)
* locals stack:                          Stack Manipulation.
                                                            (line  4515)
* locals stack <1>:                      Locals implementation.
                                                            (line 11924)
* locals types:                          Gforth locals.     (line 11501)
* locals visibility:                     Where are locals visible by name?.
                                                            (line 11669)
* locals words, ambiguous conditions:    locals-ambcond.    (line 17526)
* locals words, implementation-defined options: locals-idef.
                                                            (line 17517)
* locals words, system documentation:    The optional Locals word set.
                                                            (line 17514)
* locals, default type:                  Gforth locals.     (line 11546)
* locals, Gforth style:                  Gforth locals.     (line 11473)
* locals, maximum number in a definition: locals-idef.      (line 17518)
* locals, Standard Forth style:          Standard Forth locals.
                                                            (line 12142)
* locate:                                Locating source code definitions.
                                                            (line 13996)
* lock:                                  Semaphores.        (line 14788)
* log2:                                  Bitwise operations.
                                                            (line  4181)
* long long:                             Portability.       (line 18392)
* LOOP:                                  Counted Loops.     (line  6031)
* loop control parameters not available: core-ambcond.      (line 17144)
* loops without count:                   Simple Loops.      (line  5781)
* loops, counted:                        Counted Loops.     (line  5813)
* loops, counted, tutorial:              Counted loops Tutorial.
                                                            (line  1679)
* loops, endless:                        Simple Loops.      (line  5804)
* loops, indefinite, tutorial:           General Loops Tutorial.
                                                            (line  1614)
* lp!:                                   Stack pointer manipulation.
                                                            (line  4655)
* lp! <1>:                               Locals implementation.
                                                            (line 11939)
* lp0:                                   Stack pointer manipulation.
                                                            (line  4649)
* lp@:                                   Stack pointer manipulation.
                                                            (line  4652)
* lp@ <1>:                               Locals implementation.
                                                            (line 11936)
* lrol:                                  Bitwise operations.
                                                            (line  4206)
* lror:                                  Bitwise operations.
                                                            (line  4210)
* lshift:                                Bitwise operations.
                                                            (line  4142)
* LSHIFT, large shift counts:            core-ambcond.      (line 17173)
* LU":                                   i18n and l10n.     (line 11295)
* m*:                                    Mixed precision.   (line  3864)
* m*/:                                   Integer division.  (line  3990)
* m+:                                    Mixed precision.   (line  3862)
* m::                                    Objects Glossary.  (line 13193)
* m: usage:                              Method conveniences.
                                                            (line 12816)
* macros:                                Compiling words.   (line  8333)
* Macros:                                Macros.            (line  8424)
* macros, advanced tutorial:             Advanced macros Tutorial.
                                                            (line  2613)
* macros-wordlist:                       Substitute.        (line 11352)
* magenta-input:                         Terminal output.   (line 10871)
* make-latest:                           Making a word current.
                                                            (line  7735)
* map-vocs:                              Word Lists.        (line  9488)
* mapping block ranges to files:         file-idef.         (line 17368)
* marker:                                Forgetting words.  (line 14292)
* max:                                   Single precision.  (line  3819)
* MAX-CHAR:                              Environmental Queries.
                                                            (line  9615)
* MAX-D:                                 Environmental Queries.
                                                            (line  9644)
* max-float:                             Environmental Queries.
                                                            (line  9666)
* MAX-N:                                 Environmental Queries.
                                                            (line  9638)
* MAX-U:                                 Environmental Queries.
                                                            (line  9641)
* MAX-UD:                                Environmental Queries.
                                                            (line  9647)
* MAX-XCHAR:                             Environmental Queries.
                                                            (line  9677)
* maxalign:                              Dictionary allocation.
                                                            (line  4788)
* maxaligned:                            Address arithmetic.
                                                            (line  5141)
* maxdepth-.s:                           Examining data.    (line 14248)
* maximum depth of file input nesting:   file-idef.         (line 17361)
* maximum number of locals in a definition: locals-idef.    (line 17518)
* maximum number of word lists in search order: search-idef.
                                                            (line 17608)
* maximum size of a counted string:      core-idef.         (line 16890)
* maximum size of a definition name, in characters: core-idef.
                                                            (line 16897)
* maximum size of a parsed string:       core-idef.         (line 16894)
* maximum size of input line:            file-idef.         (line 17365)
* maximum string length for ENVIRONMENT?, in characters: core-idef.
                                                            (line 16900)
* mem+do:                                Counted Loops.     (line  6014)
* mem,:                                  Dictionary allocation.
                                                            (line  4758)
* mem-do:                                Counted Loops.     (line  6020)
* memory access words:                   Memory Access.     (line  4874)
* memory access/allocation tutorial:     Memory Tutorial.   (line  1852)
* memory alignment tutorial:             Alignment Tutorial.
                                                            (line  1991)
* memory block words:                    Memory Blocks.     (line  5190)
* memory overcommit for dictionary and stacks: Invoking Gforth.
                                                            (line   552)
* memory words:                          Memory.            (line  4660)
* memory-allocation word set:            Heap Allocation.   (line  4798)
* memory-allocation words, implementation-defined options: memory-idef.
                                                            (line 17540)
* memory-allocation words, system documentation: The optional Memory-Allocation word set.
                                                            (line 17537)
* message send:                          Object-Oriented Terminology.
                                                            (line 12585)
* metacompiler:                          cross.fs.          (line 18191)
* metacompiler <1>:                      Cross Compiler.    (line 18896)
* method:                                Object-Oriented Terminology.
                                                            (line 12580)
* method <1>:                            Objects Glossary.  (line 13203)
* method <2>:                            Class Declaration. (line 13462)
* method <3>:                            Basic Mini-OOF Usage.
                                                            (line 13500)
* method conveniences:                   Method conveniences.
                                                            (line 12810)
* method map:                            Objects Implementation.
                                                            (line 12989)
* method selector:                       Object-Oriented Terminology.
                                                            (line 12574)
* method usage:                          Basic OOF Usage.   (line 13297)
* methods:                               Objects Glossary.  (line 13207)
* methods...end-methods:                 Dividing classes.  (line 12901)
* min:                                   Single precision.  (line  3817)
* mini-oof:                              Mini-OOF.          (line 13484)
* mini-oof example:                      Mini-OOF Example.  (line 13525)
* mini-oof usage:                        Basic Mini-OOF Usage.
                                                            (line 13492)
* mini-oof.fs, differences to other models: Comparison with other object models.
                                                            (line 13771)
* minimum search order:                  search-idef.       (line 17611)
* miscellaneous words:                   Miscellaneous Words.
                                                            (line 16588)
* mixed precision arithmetic words:      Mixed precision.   (line  3862)
* mkdir-parents:                         Directories.       (line 10083)
* mod:                                   Integer division.  (line  3918)
* modf:                                  Integer division.  (line  3923)
* modf-stage2m:                          Two-stage integer division.
                                                            (line  4067)
* modifying >IN:                         How does that work?.
                                                            (line  3182)
* Modifying a word defined earlier:      Making a word current.
                                                            (line  7731)
* modifying the contents of the input buffer or a string literal: core-ambcond.
                                                            (line 17065)
* mods:                                  Integer division.  (line  3921)
* modulus:                               Integer division.  (line  3871)
* most recent definition does not have a name (IMMEDIATE): core-ambcond.
                                                            (line 17149)
* motivation for object-oriented programming: Why object-oriented programming?.
                                                            (line 12535)
* move:                                  Memory Blocks.     (line  5204)
* ms:                                    Keeping track of Time.
                                                            (line 16558)
* MS, repeatability to be expected:      facility-idef.     (line 17306)
* Multiple exits from begin:             BEGIN loops with multiple exits.
                                                            (line  6084)
* multitasker:                           Multitasker.       (line 14614)
* Must now be used inside C-LIBRARY, see C interface doc: Migrating the C interface from earlier Gforth.
                                                            (line 15353)
* mux:                                   Bitwise operations.
                                                            (line  4137)
* mwords:                                Word Lists.        (line  9458)
* n:                                     Locating source code definitions.
                                                            (line 14009)
* n, stack item type:                    Notation.          (line  3669)
* n/a:                                   User-defined TO and DEFER@.
                                                            (line  7537)
* n>r:                                   Return stack.      (line  4615)
* name:                                  The Input Stream.  (line  9278)
* name dictionary:                       Introducing the Text Interpreter.
                                                            (line  2834)
* name field address:                    Name token.        (line  8278)
* name lookup, case-sensitivity:         core-idef.         (line 16840)
* name not defined by VALUE or (LOCAL) used by TO: locals-ambcond.
                                                            (line 17532)
* name not defined by VALUE used by TO:  core-ambcond.      (line 17152)
* name not found:                        core-ambcond.      (line 16998)
* name not found (', POSTPONE, ['], [COMPILE]): core-ambcond.
                                                            (line 17157)
* name token:                            Name token.        (line  8191)
* name$:                                 widget methods.    (line 19094)
* name, maximum length:                  core-idef.         (line 16897)
* name>compile:                          Name token.        (line  8244)
* name>interpret:                        Name token.        (line  8241)
* name>link:                             Name token.        (line  8256)
* name>string:                           Name token.        (line  8247)
* names for defined words:               Supplying names.   (line  7080)
* NaN:                                   Floating Point.    (line  4493)
* native@:                               i18n and l10n.     (line 11299)
* needs:                                 Forth source files.
                                                            (line  9867)
* negate:                                Single precision.  (line  3813)
* negative increment for counted loops:  Counted Loops.     (line  5884)
* Neon model:                            Comparison with other object models.
                                                            (line 13721)
* nested colon definitions:              Quotations.        (line  7050)
* new:                                   Basic Mini-OOF Usage.
                                                            (line 13515)
* new-color::                            widget methods.    (line 19213)
* newline:                               String and character literals.
                                                            (line  5371)
* newline character on input:            core-idef.         (line 16885)
* newtask:                               Basic multi-tasking.
                                                            (line 14639)
* newtask4:                              Basic multi-tasking.
                                                            (line 14648)
* NEXT:                                  Counted Loops.     (line  6040)
* NEXT, direct threaded:                 Threading.         (line 18440)
* NEXT, indirect threaded:               Threading.         (line 18429)
* next-arg:                              OS command line arguments.
                                                            (line 11405)
* next-case:                             Arbitrary control structures.
                                                            (line  6306)
* nextname:                              Supplying names.   (line  7084)
* NFA:                                   Name token.        (line  8278)
* nip:                                   Data stack.        (line  4522)
* nocov[:                                Code Coverage.     (line 14557)
* non-graphic characters and EMIT:       core-idef.         (line 16819)
* non-relocatable image files:           Non-Relocatable Image Files.
                                                            (line 18089)
* noname:                                Anonymous Definitions.
                                                            (line  7021)
* noname-from:                           Creating from a prototype.
                                                            (line  7715)
* noop:                                  Execution token.   (line  8178)
* notation of glossary entries:          Notation.          (line  3587)
* notfound:                              Dealing with existing Recognizers.
                                                            (line  9130)
* nothrow:                               Exception Handling.
                                                            (line  6504)
* nr>:                                   Return stack.      (line  4617)
* ns:                                    Keeping track of Time.
                                                            (line 16560)
* nt:                                    Locating exception source.
                                                            (line 14103)
* nt (name token):                       Name token.        (line  8191)
* NT Forth performance:                  Performance.       (line 18819)
* nt input format:                       Literals in source code.
                                                            (line  3569)
* nt token input format:                 Literals in source code.
                                                            (line  3569)
* ntime:                                 Keeping track of Time.
                                                            (line 16575)
* number conversion:                     Number Conversion. (line  8838)
* number conversion - traps for the unwary: Number Conversion.
                                                            (line  8875)
* number of bits in one address unit:    core-idef.         (line 16917)
* number representation and arithmetic:  core-idef.         (line 16921)
* numeric comparison words:              Numeric comparison.
                                                            (line  4229)
* numeric output - formatted:            Formatted numeric output.
                                                            (line 10461)
* numeric output - simple/free-format:   Simple numeric output.
                                                            (line 10412)
* numeric output, FP:                    Floating-point output.
                                                            (line 10612)
* nw:                                    Locating uses of a word.
                                                            (line 14056)
* o>:                                    Mini-OOF2.         (line 13697)
* object:                                Object-Oriented Terminology.
                                                            (line 12567)
* object <1>:                            Objects Glossary.  (line 13212)
* object <2>:                            Basic Mini-OOF Usage.
                                                            (line 13497)
* object allocation options:             Creating objects.  (line 12728)
* object class:                          The Objects base class.
                                                            (line 12719)
* object creation:                       Creating objects.  (line 12728)
* object interfaces:                     Object Interfaces. (line 12937)
* object models, comparison:             Comparison with other object models.
                                                            (line 13714)
* object-':                              The OOF base class.
                                                            (line 13423)
* object-::                              The OOF base class.
                                                            (line 13389)
* object-:::                             The OOF base class.
                                                            (line 13401)
* object-asptr:                          The OOF base class.
                                                            (line 13393)
* object-bind:                           The OOF base class.
                                                            (line 13412)
* object-bound:                          The OOF base class.
                                                            (line 13414)
* object-class:                          The OOF base class.
                                                            (line 13366)
* object-class?:                         The OOF base class.
                                                            (line 13370)
* object-definitions:                    The OOF base class.
                                                            (line 13368)
* object-dispose:                        The OOF base class.
                                                            (line 13380)
* object-endwith:                        The OOF base class.
                                                            (line 13434)
* object-init:                           The OOF base class.
                                                            (line 13378)
* object-is:                             The OOF base class.
                                                            (line 13418)
* object-link:                           The OOF base class.
                                                            (line 13416)
* object-map discussion:                 Objects Implementation.
                                                            (line 12985)
* object-new:                            The OOF base class.
                                                            (line 13385)
* object-new[]:                          The OOF base class.
                                                            (line 13387)
* object-oriented programming:           Objects.           (line 12606)
* object-oriented programming <1>:       OOF.               (line 13256)
* object-oriented programming motivation: Why object-oriented programming?.
                                                            (line 12535)
* object-oriented programming style:     Object-Oriented Programming Style.
                                                            (line 12743)
* object-oriented terminology:           Object-Oriented Terminology.
                                                            (line 12560)
* object-postpone:                       The OOF base class.
                                                            (line 13425)
* object-ptr:                            The OOF base class.
                                                            (line 13391)
* object-self:                           The OOF base class.
                                                            (line 13407)
* object-super:                          The OOF base class.
                                                            (line 13403)
* object-with:                           The OOF base class.
                                                            (line 13432)
* object-[]:                             The OOF base class.
                                                            (line 13395)
* objects:                               Objects.           (line 12606)
* objects, basic usage:                  Basic Objects Usage.
                                                            (line 12657)
* objects.fs:                            Objects.           (line 12606)
* objects.fs <1>:                        OOF.               (line 13256)
* objects.fs Glossary:                   Objects Glossary.  (line 13099)
* objects.fs implementation:             Objects Implementation.
                                                            (line 12985)
* objects.fs properties:                 Properties of the Objects model.
                                                            (line 12623)
* of:                                    Arbitrary control structures.
                                                            (line  6310)
* off:                                   Boolean Flags.     (line  3771)
* on:                                    Boolean Flags.     (line  3768)
* once:                                  Debugging.         (line 14365)
* Only:                                  Word Lists.        (line  9409)
* oof:                                   OOF.               (line 13256)
* oof.fs:                                Objects.           (line 12606)
* oof.fs <1>:                            OOF.               (line 13256)
* oof.fs base class:                     The OOF base class.
                                                            (line 13352)
* oof.fs properties:                     Properties of the OOF model.
                                                            (line 13269)
* oof.fs usage:                          Basic OOF Usage.   (line 13292)
* oof.fs, differences to other models:   Comparison with other object models.
                                                            (line 13756)
* open-blocks:                           Blocks.            (line 10304)
* open-dir:                              Directories.       (line 10049)
* open-file:                             General files.     (line  9913)
* open-lib:                              Low-Level C Interface Words.
                                                            (line 15282)
* open-path-file:                        General Search Paths.
                                                            (line 10152)
* open-pipe:                             Pipes.             (line 11139)
* operating system - passing commands:   Passing Commands to the OS.
                                                            (line 16526)
* operator's terminal facilities available: core-other.     (line 17193)
* opt::                                  User-defined compile-comma.
                                                            (line  7580)
* options on the command line:           Invoking Gforth.   (line   473)
* or:                                    Bitwise operations.
                                                            (line  4131)
* order:                                 Word Lists.        (line  9413)
* orig, control-flow stack item:         Arbitrary control structures.
                                                            (line  6221)
* OS command line arguments:             OS command line arguments.
                                                            (line 11396)
* os-class:                              Environmental Queries.
                                                            (line  9727)
* os-type:                               Environmental Queries.
                                                            (line  9731)
* other system documentation, block words: block-other.     (line 17257)
* other system documentation, core words: core-other.       (line 17189)
* out:                                   Miscellaneous output.
                                                            (line 10722)
* outer interpreter:                     Introducing the Text Interpreter.
                                                            (line  2797)
* outer interpreter <1>:                 Stacks and Postfix notation.
                                                            (line  2905)
* outer interpreter <2>:                 The Text Interpreter.
                                                            (line  8636)
* outfile-execute:                       Redirection.       (line 10009)
* outfile-id:                            Redirection.       (line 10012)
* output in pipes:                       Gforth in pipes.   (line   853)
* Output Redirection:                    Redirection.       (line  9994)
* output to terminal:                    Terminal output.   (line 10799)
* over:                                  Data stack.        (line  4526)
* overcommit memory for dictionary and stacks: Invoking Gforth.
                                                            (line   552)
* overflow of the pictured numeric output string: core-ambcond.
                                                            (line 17068)
* overrides:                             Objects Glossary.  (line 13215)
* overrides usage:                       Basic Objects Usage.
                                                            (line 12680)
* pad:                                   Memory Blocks.     (line  5241)
* PAD size:                              core-idef.         (line 16959)
* PAD use by nonstandard words:          core-other.        (line 17190)
* page:                                  Terminal output.   (line 10816)
* par-split:                             widget methods.    (line 19187)
* parameter stack:                       Stack Manipulation.
                                                            (line  4507)
* parameters are not of the same type (DO, ?DO, WITHIN): core-ambcond.
                                                            (line 17160)
* parent class:                          Object-Oriented Terminology.
                                                            (line 12597)
* parent class binding:                  Class Binding.     (line 12783)
* parent-w:                              widget methods.    (line 19088)
* parse:                                 The Input Stream.  (line  9261)
* parse area:                            The Text Interpreter.
                                                            (line  8677)
* parse-name:                            The Input Stream.  (line  9271)
* parse-word:                            The Input Stream.  (line  9274)
* parsed string overflow:                core-ambcond.      (line 17071)
* parsed string, maximum size:           core-idef.         (line 16894)
* parsing words:                         How does that work?.
                                                            (line  3170)
* parsing words <1>:                     How does that work?.
                                                            (line  3194)
* parsing words <2>:                     The Text Interpreter.
                                                            (line  8699)
* pass:                                  Basic multi-tasking.
                                                            (line 14681)
* patching threaded code:                Dynamic Superinstructions.
                                                            (line 18636)
* path for included:                     Search Paths.      (line 10090)
* path+:                                 General Search Paths.
                                                            (line 10173)
* path=:                                 General Search Paths.
                                                            (line 10176)
* pause:                                 Basic multi-tasking.
                                                            (line 14722)
* pedigree of Gforth:                    Origin.            (line 19356)
* perform:                               Execution token.   (line  8173)
* performance of some Forth interpreters: Performance.      (line 18803)
* persistent form of dictionary:         Image Files.       (line 17975)
* PFE performance:                       Performance.       (line 18819)
* pi:                                    Floating Point.    (line  4439)
* pick:                                  Data stack.        (line  4536)
* pictured numeric output:               Formatted numeric output.
                                                            (line 10461)
* pictured numeric output buffer, size:  core-idef.         (line 16955)
* pictured numeric output string, overflow: core-ambcond.   (line 17068)
* pipes, creating your own:              Pipes.             (line 11135)
* pipes, Gforth as part of:              Gforth in pipes.   (line   842)
* postpone:                              Macros.            (line  8441)
* POSTPONE applied to [IF]:              programming-ambcond.
                                                            (line 17590)
* POSTPONE or [COMPILE] applied to TO:   core-ambcond.      (line 17165)
* postpone tutorial:                     POSTPONE Tutorial. (line  2531)
* postpone,:                             Compilation token. (line  8319)
* Pountain's object-oriented model:      Comparison with other object models.
                                                            (line 13736)
* pow2?:                                 Bitwise operations.
                                                            (line  4185)
* precision:                             Floating-point output.
                                                            (line 10640)
* precompiled Forth code:                Image Files.       (line 17975)
* prefix `:                              Execution token.   (line  8096)
* prepend-where:                         Locating uses of a word.
                                                            (line 14088)
* preserve:                              Deferred Words.    (line  7882)
* previous:                              Word Lists.        (line  9397)
* previous, search order empty:          search-ambcond.    (line 17625)
* primitive source format:               Automatic Generation.
                                                            (line 18679)
* primitive-centric threaded code:       Direct or Indirect Threaded?.
                                                            (line 18498)
* primitives, assembly code listing:     Produced code.     (line 18795)
* primitives, automatic generation:      Automatic Generation.
                                                            (line 18670)
* primitives, implementation:            Primitives.        (line 18667)
* primitives, keeping the TOS in a register: TOS Optimization.
                                                            (line 18749)
* prims2x.fs:                            Automatic Generation.
                                                            (line 18670)
* print:                                 Objects Glossary.  (line 13222)
* printdebugdata:                        Debugging.         (line 14350)
* private discussion:                    Classes and Scoping.
                                                            (line 12890)
* procedures, tutorial:                  Colon Definitions Tutorial.
                                                            (line  1206)
* process-option:                        Modifying the Startup Sequence.
                                                            (line 18353)
* program data space available:          core-other.        (line 17199)
* programming style, arbitrary control structures: Arbitrary control structures.
                                                            (line  6330)
* programming style, locals:             Locals programming style.
                                                            (line 11861)
* programming style, object-oriented:    Object-Oriented Programming Style.
                                                            (line 12743)
* programming tools:                     Programming Tools. (line 13973)
* programming-tools words, ambiguous conditions: programming-ambcond.
                                                            (line 17572)
* programming-tools words, implementation-defined options: programming-idef.
                                                            (line 17552)
* programming-tools words, system documentation: The optional Programming-Tools word set.
                                                            (line 17549)
* prompt:                                core-idef.         (line 16969)
* pronounciation of words:               Notation.          (line  3619)
* protected:                             Objects Glossary.  (line 13226)
* protected discussion:                  Classes and Scoping.
                                                            (line 12890)
* pthread:                               Pthreads.          (line 14623)
* ptr:                                   Class Declaration. (line 13446)
* public:                                Objects Glossary.  (line 13229)
* query:                                 Input Sources.     (line  8830)
* quit:                                  Miscellaneous Words.
                                                            (line 16591)
* quotations:                            Quotations.        (line  7050)
* r, stack item type:                    Notation.          (line  3677)
* r/o:                                   General files.     (line  9897)
* r/w:                                   General files.     (line  9899)
* r>:                                    Return stack.      (line  4601)
* r@:                                    Return stack.      (line  4603)
* raise:                                 widget methods.    (line 19121)
* ranges for integer types:              core-idef.         (line 16925)
* rdrop:                                 Return stack.      (line  4605)
* re-color:                              widget methods.    (line 19236)
* re-emoji-color:                        widget methods.    (line 19244)
* re-fade-color:                         widget methods.    (line 19248)
* re-text-color:                         widget methods.    (line 19240)
* re-text-emoji-fade-color:              widget methods.    (line 19252)
* read-csv:                              CSV Reader.        (line 11388)
* read-dir:                              Directories.       (line 10053)
* read-file:                             General files.     (line  9924)
* read-line:                             General files.     (line  9930)
* read-only data space regions:          core-idef.         (line 16932)
* reading from file positions not yet written: file-ambcond.
                                                            (line 17386)
* rec-body:                              Dealing with existing Recognizers.
                                                            (line  9159)
* rec-dtick:                             Dealing with existing Recognizers.
                                                            (line  9155)
* rec-float:                             Dealing with existing Recognizers.
                                                            (line  9139)
* rec-moof2:                             Mini-OOF2.         (line 13703)
* rec-nt:                                Dealing with existing Recognizers.
                                                            (line  9133)
* rec-num:                               Dealing with existing Recognizers.
                                                            (line  9136)
* rec-string:                            Dealing with existing Recognizers.
                                                            (line  9142)
* rec-tick:                              Dealing with existing Recognizers.
                                                            (line  9151)
* rec-to:                                Dealing with existing Recognizers.
                                                            (line  9146)
* receiving object:                      Object-Oriented Terminology.
                                                            (line 12591)
* reciprocal of integer:                 Two-stage integer division.
                                                            (line  4013)
* recognize:                             Dealing with existing Recognizers.
                                                            (line  9169)
* recognizer-sequence::                  Dealing with existing Recognizers.
                                                            (line  9172)
* Recognizers normal usage:              Default Recognizers.
                                                            (line  9021)
* Recognizers, dealing with:             Dealing with existing Recognizers.
                                                            (line  9105)
* recongizers:                           Recognizers.       (line  9007)
* records:                               Structures.        (line 12174)
* records tutorial:                      Arrays and Records Tutorial.
                                                            (line  2506)
* recover (old Gforth versions):         Exception Handling.
                                                            (line  6589)
* recurse:                               Calls and returns. (line  6376)
* RECURSE appears after DOES>:           core-ambcond.      (line 17113)
* recursion tutorial:                    Recursion Tutorial.
                                                            (line  1732)
* recursive:                             Calls and returns. (line  6372)
* recursive definitions:                 Calls and returns. (line  6366)
* Redirection:                           Redirection.       (line  9994)
* refill:                                The Input Stream.  (line  9290)
* regexps:                               Regular Expressions.
                                                            (line 13784)
* relocating loader:                     Image File Background.
                                                            (line 18038)
* relocation at load-time:               Image File Background.
                                                            (line 18029)
* relocation at run-time:                Image File Background.
                                                            (line 18023)
* remainder:                             Integer division.  (line  3871)
* rename-file:                           General files.     (line  9921)
* REPEAT:                                Arbitrary control structures.
                                                            (line  6278)
* repeatability to be expected from the execution of MS: facility-idef.
                                                            (line 17306)
* replace-word:                          Debugging.         (line 14383)
* replaces:                              Substitute.        (line 11355)
* Replication:                           Dynamic Superinstructions.
                                                            (line 18537)
* report the words used in your program: Standard Report.   (line 16671)
* reposition-file:                       General files.     (line  9970)
* REPOSITION-FILE, outside the file's boundaries: file-ambcond.
                                                            (line 17382)
* represent:                             Floating-point output.
                                                            (line 10702)
* REPRESENT, results when float is out of range: floating-idef.
                                                            (line 17419)
* require:                               Forth source files.
                                                            (line  9864)
* require, placement in files:           Emacs Tags.        (line 17858)
* required:                              Forth source files.
                                                            (line  9858)
* reserving data space:                  Dictionary allocation.
                                                            (line  4696)
* resize:                                Heap Allocation.   (line  4821)
* resize-file:                           General files.     (line  9974)
* resized:                               widget methods.    (line 19190)
* restart:                               Basic multi-tasking.
                                                            (line 14717)
* restore:                               Exception Handling.
                                                            (line  6622)
* restore-input:                         Input Sources.     (line  8815)
* RESTORE-INPUT, Argument type mismatch: core-ambcond.      (line 17116)
* restrict:                              Interpretation and Compilation Semantics.
                                                            (line  7995)
* Result out of range:                   Integer division.  (line  3871)
* result out of range:                   core-ambcond.      (line 17074)
* Result out of range (on integer division): Integer division.
                                                            (line  3998)
* return stack:                          Stack Manipulation.
                                                            (line  4512)
* return stack and locals:               Return stack.      (line  4592)
* return stack dump with gforth-fast:    Error messages.    (line 16650)
* return stack manipulation words:       Return stack.      (line  4592)
* return stack space available:          core-other.        (line 17204)
* return stack tutorial:                 Return Stack Tutorial.
                                                            (line  1800)
* return stack underflow:                core-ambcond.      (line 17085)
* return-stack-cells:                    Environmental Queries.
                                                            (line  9650)
* returning from a definition:           Calls and returns. (line  6366)
* reveal:                                Creating from a prototype.
                                                            (line  7708)
* rol:                                   Bitwise operations.
                                                            (line  4214)
* roll:                                  Data stack.        (line  4547)
* Root:                                  Word Lists.        (line  9464)
* ror:                                   Bitwise operations.
                                                            (line  4217)
* rot:                                   Data stack.        (line  4539)
* rounding of floating-point numbers:    floating-idef.     (line 17423)
* rp!:                                   Stack pointer manipulation.
                                                            (line  4647)
* rp0:                                   Stack pointer manipulation.
                                                            (line  4642)
* rp@:                                   Stack pointer manipulation.
                                                            (line  4645)
* rshift:                                Bitwise operations.
                                                            (line  4145)
* RSHIFT, large shift counts:            core-ambcond.      (line 17173)
* run-time code generation, tutorial:    Advanced macros Tutorial.
                                                            (line  2613)
* running Gforth:                        Invoking Gforth.   (line   473)
* running image files:                   Running Image Files.
                                                            (line 18226)
* Rydqvist, Goran:                       Emacs and Gforth.  (line 17807)
* S":                                    String and character literals.
                                                            (line  5327)
* S", number of string buffers:          file-idef.         (line 17372)
* S", size of string buffer:             file-idef.         (line 17376)
* s+:                                    String words.      (line  5472)
* s//:                                   Regular Expressions.
                                                            (line 13956)
* s>>:                                   Regular Expressions.
                                                            (line 13943)
* s>d:                                   Double precision.  (line  3843)
* s>f:                                   Floating Point.    (line  4326)
* s>number?:                             Line input and conversion.
                                                            (line 11080)
* s>unumber?:                            Line input and conversion.
                                                            (line 11083)
* safe/string:                           String words.      (line  5442)
* save-buffer:                           Blocks.            (line 10364)
* save-buffers:                          Blocks.            (line 10360)
* save-cov:                              Code Coverage.     (line 14605)
* save-input:                            Input Sources.     (line  8810)
* save-mem:                              Heap Allocation.   (line  4831)
* savesystem:                            Non-Relocatable Image Files.
                                                            (line 18103)
* savesystem during gforthmi:            gforthmi.          (line 18176)
* scan:                                  String words.      (line  5422)
* scan-back:                             String words.      (line  5427)
* scope:                                 Where are locals visible by name?.
                                                            (line 11674)
* scope of locals:                       Where are locals visible by name?.
                                                            (line 11669)
* scoping and classes:                   Classes and Scoping.
                                                            (line 12875)
* scr:                                   Blocks.            (line 10327)
* scrolled:                              actor methods.     (line 19040)
* seal:                                  Word Lists.        (line  9474)
* search:                                String words.      (line  5416)
* search order stack:                    Word Lists.        (line  9334)
* search order, maximum depth:           search-idef.       (line 17608)
* search order, minimum:                 search-idef.       (line 17611)
* search order, tutorial:                Wordlists and Search Order Tutorial.
                                                            (line  2700)
* search path control, source files:     Source Search Paths.
                                                            (line 10124)
* search path control, source files <1>: General Search Paths.
                                                            (line 10147)
* search path for files:                 Search Paths.      (line 10090)
* search-order words, ambiguous conditions: search-ambcond. (line 17616)
* search-order words, implementation-defined options: search-idef.
                                                            (line 17607)
* search-order words, system documentation: The optional Search-Order word set.
                                                            (line 17604)
* search-wordlist:                       Word Lists.        (line  9440)
* see:                                   Examining compiled code.
                                                            (line 14115)
* see tutorial:                          Decompilation Tutorial.
                                                            (line  1238)
* SEE, source and format of output:      programming-idef.  (line 17564)
* see-code:                              Examining compiled code.
                                                            (line 14134)
* see-code-range:                        Examining compiled code.
                                                            (line 14148)
* select:                                Boolean Flags.     (line  3774)
* selection control structures:          Selection.         (line  5698)
* selector:                              Object-Oriented Terminology.
                                                            (line 12574)
* selector <1>:                          Objects Glossary.  (line 13233)
* selector implementation, class:        Objects Implementation.
                                                            (line 12993)
* selector invocation:                   Object-Oriented Terminology.
                                                            (line 12585)
* selector invocation, restrictions:     Basic Objects Usage.
                                                            (line 12709)
* selector invocation, restrictions <1>: Basic OOF Usage.   (line 13342)
* selector usage:                        Basic Objects Usage.
                                                            (line 12659)
* selectors and stack effects:           Object-Oriented Programming Style.
                                                            (line 12745)
* selectors common to hardly-related classes: Object Interfaces.
                                                            (line 12942)
* semantics tutorial:                    Interpretation and Compilation Semantics and Immediacy Tutorial.
                                                            (line  2199)
* semantics, interpretation and compilation: Interpretation and Compilation Semantics.
                                                            (line  7945)
* semaphore:                             Semaphores.        (line 14784)
* send-event:                            Message queues.    (line 14844)
* set:                                   actor methods.     (line 19079)
* set->comp:                             Header methods.    (line 16355)
* set->int:                              Header methods.    (line 16343)
* set-current:                           Word Lists.        (line  9365)
* set-dir:                               Directories.       (line 10076)
* set-does>:                             CREATE..DOES> details.
                                                            (line  7395)
* set-execute:                           Header methods.    (line 16232)
* set-forth-recognize:                   Dealing with existing Recognizers.
                                                            (line  9183)
* set-name>link:                         Header methods.    (line 16374)
* set-name>string:                       Header methods.    (line 16370)
* set-optimizer:                         User-defined compile-comma.
                                                            (line  7574)
* set-order:                             Word Lists.        (line  9374)
* set-precision:                         Floating-point output.
                                                            (line 10644)
* set-recognizers:                       Dealing with existing Recognizers.
                                                            (line  9166)
* set-to:                                User-defined TO and DEFER@.
                                                            (line  7533)
* sf!:                                   Memory Access.     (line  4906)
* sf@:                                   Memory Access.     (line  4902)
* sf@ or sf! used with an address that is not single-float aligned: floating-ambcond.
                                                            (line 17456)
* sfalign:                               Dictionary allocation.
                                                            (line  4780)
* sfaligned:                             Address arithmetic.
                                                            (line  5124)
* sffield::                              Forth200x Structures.
                                                            (line 12507)
* sfloat%:                               Structure Glossary.
                                                            (line 12437)
* sfloat+:                               Address arithmetic.
                                                            (line  5119)
* sfloat/:                               Address arithmetic.
                                                            (line  5122)
* sfloats:                               Address arithmetic.
                                                            (line  5115)
* sf_, stack item type:                  Notation.          (line  3688)
* sh:                                    Passing Commands to the OS.
                                                            (line 16529)
* sh-get:                                Passing Commands to the OS.
                                                            (line 16541)
* Shared libraries in C interface:       Declaring OS-level libraries.
                                                            (line 15173)
* shell commands:                        Passing Commands to the OS.
                                                            (line 16526)
* shift-args:                            OS command line arguments.
                                                            (line 11439)
* short-where:                           Locating uses of a word.
                                                            (line 14081)
* show:                                  actor methods.     (line 19070)
* show-you:                              actor methods.     (line 19082)
* sign:                                  Formatted numeric output.
                                                            (line 10525)
* sign extension:                        Special Memory Accesses.
                                                            (line  4921)
* silent exiting from Gforth:            Gforth in pipes.   (line   855)
* simple defining words:                 CREATE.            (line  6696)
* simple loops:                          Simple Loops.      (line  5781)
* simple-fkey-string:                    Single-key input.  (line 11054)
* simple-see:                            Examining compiled code.
                                                            (line 14124)
* simple-see-range:                      Examining compiled code.
                                                            (line 14131)
* single precision arithmetic words:     Single precision.  (line  3792)
* single-assignment style for locals:    Locals programming style.
                                                            (line 11880)
* single-cell numbers, input format:     Literals in source code.
                                                            (line  3456)
* single-key input:                      Single-key input.  (line 10877)
* singlestep Debugger:                   Singlestep Debugger.
                                                            (line 14480)
* size of buffer at WORD:                core-idef.         (line 16935)
* size of the dictionary and the stacks: Invoking Gforth.   (line   521)
* size of the keyboard terminal buffer:  core-idef.         (line 16948)
* size of the pictured numeric output buffer: core-idef.    (line 16955)
* size of the scratch area returned by PAD: core-idef.      (line 16959)
* size parameters for command-line options: Invoking Gforth.
                                                            (line   521)
* skip:                                  String words.      (line  5429)
* SLiteral:                              Literals.          (line  8403)
* slurp-fid:                             General files.     (line  9979)
* slurp-file:                            General files.     (line  9976)
* sm/rem:                                Integer division.  (line  3947)
* source:                                The Text Interpreter.
                                                            (line  8756)
* source code for exception:             Locating exception source.
                                                            (line 14101)
* source code of a word:                 Locating source code definitions.
                                                            (line 13976)
* source location of error or debugging output in Emacs: Emacs and Gforth.
                                                            (line 17822)
* source-id:                             Input Sources.     (line  8801)
* SOURCE-ID, behaviour when BLK is non-zero: file-ambcond.  (line 17406)
* sourcefilename:                        Forth source files.
                                                            (line  9876)
* sourceline#:                           Forth source files.
                                                            (line  9883)
* sp!:                                   Stack pointer manipulation.
                                                            (line  4633)
* sp0:                                   Stack pointer manipulation.
                                                            (line  4628)
* sp@:                                   Stack pointer manipulation.
                                                            (line  4631)
* space:                                 Miscellaneous output.
                                                            (line 10716)
* space delimiters:                      core-idef.         (line 16856)
* spaces:                                Miscellaneous output.
                                                            (line 10719)
* span:                                  Line input and conversion.
                                                            (line 11128)
* spawn:                                 Cilk.              (line 14895)
* spawn1:                                Cilk.              (line 14901)
* spawn2:                                Cilk.              (line 14904)
* speed, startup:                        Startup speed.     (line   885)
* split:                                 widget methods.    (line 19145)
* stability of Gforth:                   Stability Goals.   (line   439)
* stack depth changes during interpretation: Stack depth changes.
                                                            (line 16714)
* stack effect:                          Notation.          (line  3597)
* Stack effect design, tutorial:         Designing the stack effect Tutorial.
                                                            (line  1402)
* stack effect of DOES>-parts:           User-defined defining words using CREATE.
                                                            (line  7277)
* stack effect of included files:        Forth source files.
                                                            (line  9829)
* stack effects of selectors:            Object-Oriented Programming Style.
                                                            (line 12745)
* stack empty:                           core-ambcond.      (line 17085)
* stack item types:                      Notation.          (line  3659)
* stack manipulation tutorial:           Stack Manipulation Tutorial.
                                                            (line  1093)
* stack manipulation words:              Stack Manipulation.
                                                            (line  4505)
* stack manipulation words, floating-point stack: Floating point stack.
                                                            (line  4566)
* stack manipulation words, return stack: Return stack.     (line  4592)
* stack manipulations words, data stack: Data stack.        (line  4520)
* stack overflow:                        core-ambcond.      (line 17032)
* stack pointer manipulation words:      Stack pointer manipulation.
                                                            (line  4628)
* stack size default:                    Stack and Dictionary Sizes.
                                                            (line 18205)
* stack size, cache-friendly:            Stack and Dictionary Sizes.
                                                            (line 18218)
* stack space available:                 core-other.        (line 17209)
* stack tutorial:                        Stack Tutorial.    (line  1029)
* stack underflow:                       core-ambcond.      (line 17085)
* stack-cells:                           Environmental Queries.
                                                            (line  9653)
* stack-effect comments, tutorial:       Stack-Effect Comments Tutorial.
                                                            (line  1255)
* stacksize:                             Basic multi-tasking.
                                                            (line 14655)
* stacksize4:                            Basic multi-tasking.
                                                            (line 14658)
* staged/-divisor:                       Two-stage integer division.
                                                            (line  4098)
* staged/-size:                          Two-stage integer division.
                                                            (line  4056)
* Standard conformance of Gforth:        Standard conformance.
                                                            (line 16755)
* starting Gforth tutorial:              Starting Gforth Tutorial.
                                                            (line   972)
* startup sequence for image file:       Modifying the Startup Sequence.
                                                            (line 18303)
* Startup speed:                         Startup speed.     (line   885)
* state - effect on the text interpreter: How does that work?.
                                                            (line  3198)
* STATE values:                          core-idef.         (line 16979)
* state-smart words (are a bad idea):    Combined words.    (line  8051)
* static:                                Class Declaration. (line 13467)
* status-color:                          Terminal output.   (line 10853)
* stderr:                                General files.     (line  9988)
* stderr and pipes:                      Gforth in pipes.   (line   880)
* stdin:                                 General files.     (line  9982)
* stdout:                                General files.     (line  9985)
* stop:                                  Basic multi-tasking.
                                                            (line 14708)
* stop-ns:                               Basic multi-tasking.
                                                            (line 14711)
* str<:                                  String words.      (line  5408)
* str=:                                  String words.      (line  5406)
* str=?:                                 Regular Expressions.
                                                            (line 13880)
* String input format:                   Literals in source code.
                                                            (line  3547)
* string larger than pictured numeric output area (f., fe., fs.): floating-ambcond.
                                                            (line 17507)
* string literals:                       String and character literals.
                                                            (line  5304)
* string longer than a counted string returned by WORD: core-ambcond.
                                                            (line 17169)
* string words with $:                   $tring words.      (line  5499)
* string,:                               Counted string words.
                                                            (line  5678)
* string-parse:                          The Input Stream.  (line  9266)
* string-prefix?:                        String words.      (line  5410)
* string-suffix?:                        String words.      (line  5413)
* strings - see character strings:       String representations.
                                                            (line  5281)
* strings tutorial:                      Characters and Strings Tutorial.
                                                            (line  1942)
* struct:                                Structure Glossary.
                                                            (line 12442)
* struct usage:                          Structure Usage.   (line 12260)
* structs tutorial:                      Arrays and Records Tutorial.
                                                            (line  2506)
* structure extension:                   Structure Usage.   (line 12305)
* structure glossary:                    Structure Glossary.
                                                            (line 12397)
* structure implementation:              Structure Implementation.
                                                            (line 12368)
* structure naming convention:           Structure Naming Convention.
                                                            (line 12344)
* structure naming convention <1>:       Structure Naming Convention.
                                                            (line 12358)
* structure of Forth programs:           Forth is written in Forth.
                                                            (line  3341)
* structure usage:                       Structure Usage.   (line 12260)
* structures:                            Structures.        (line 12174)
* structures containing arrays:          Structure Usage.   (line 12317)
* structures containing structures:      Structure Usage.   (line 12297)
* Structures in Forth200x:               Forth200x Structures.
                                                            (line 12448)
* structures using address arithmetic:   Why explicit structure support?.
                                                            (line 12187)
* sub-list?:                             Locals implementation.
                                                            (line 12014)
* substitute:                            Substitute.        (line 11367)
* success-color:                         Terminal output.   (line 10847)
* superclass binding:                    Class Binding.     (line 12783)
* Superinstructions:                     Dynamic Superinstructions.
                                                            (line 18537)
* swap:                                  Data stack.        (line  4534)
* symmetric division:                    Integer division.  (line  3876)
* Synonym:                               Aliases.           (line  7916)
* synonyms:                              Aliases.           (line  7905)
* syntax tutorial:                       Syntax Tutorial.   (line   983)
* system:                                Passing Commands to the OS.
                                                            (line 16533)
* system dictionary space required, in address units: core-other.
                                                            (line 17214)
* system documentation:                  Standard conformance.
                                                            (line 16794)
* system documentation, block words:     The optional Block word set.
                                                            (line 17220)
* system documentation, core words:      The Core Words.    (line 16809)
* system documentation, double words:    The optional Double Number word set.
                                                            (line 17266)
* system documentation, exception words: The optional Exception word set.
                                                            (line 17275)
* system documentation, facility words:  The optional Facility word set.
                                                            (line 17290)
* system documentation, file words:      The optional File-Access word set.
                                                            (line 17322)
* system documentation, floating-point words: The optional Floating-Point word set.
                                                            (line 17412)
* system documentation, locals words:    The optional Locals word set.
                                                            (line 17514)
* system documentation, memory-allocation words: The optional Memory-Allocation word set.
                                                            (line 17537)
* system documentation, programming-tools words: The optional Programming-Tools word set.
                                                            (line 17549)
* system documentation, search-order words: The optional Search-Order word set.
                                                            (line 17604)
* system prompt:                         core-idef.         (line 16969)
* s\":                                   String and character literals.
                                                            (line  5309)
* table:                                 Word Lists.        (line  9385)
* TAGS file:                             Emacs Tags.        (line 17858)
* target compiler:                       cross.fs.          (line 18191)
* target compiler <1>:                   Cross Compiler.    (line 18896)
* task:                                  Basic multi-tasking.
                                                            (line 14643)
* task-local data:                       Task-local data.   (line 14732)
* terminal buffer, size:                 core-idef.         (line 16948)
* terminal input buffer:                 The Text Interpreter.
                                                            (line  8650)
* terminal output:                       Terminal output.   (line 10799)
* terminal size:                         Terminal output.   (line 10810)
* terminology for object-oriented programming: Object-Oriented Terminology.
                                                            (line 12560)
* text interpreter:                      Introducing the Text Interpreter.
                                                            (line  2797)
* text interpreter <1>:                  Stacks and Postfix notation.
                                                            (line  2905)
* text interpreter <2>:                  The Text Interpreter.
                                                            (line  8636)
* text interpreter - effect of state:    How does that work?.
                                                            (line  3198)
* text interpreter - input sources:      The Text Interpreter.
                                                            (line  8737)
* text interpreter - input sources <1>:  Input Sources.     (line  8789)
* text-color::                           widget methods.    (line 19216)
* text-emoji-color::                     widget methods.    (line 19220)
* text-emoji-fade-color::                widget methods.    (line 19230)
* THEN:                                  Arbitrary control structures.
                                                            (line  6235)
* third:                                 Data stack.        (line  4528)
* this:                                  Objects Glossary.  (line 13238)
* this and catch:                        Objects Implementation.
                                                            (line 13022)
* this implementation:                   Objects Implementation.
                                                            (line 13022)
* this usage:                            Method conveniences.
                                                            (line 12816)
* ThisForth performance:                 Performance.       (line 18819)
* threaded code implementation:          Threading.         (line 18423)
* threading words:                       Threading Words.   (line 16381)
* threading, direct or indirect?:        Direct or Indirect Threaded?.
                                                            (line 18488)
* threading-method:                      Threading Words.   (line 16444)
* throw:                                 Exception Handling.
                                                            (line  6425)
* THROW-codes used in the system:        exception-idef.    (line 17279)
* thru:                                  Blocks.            (line 10372)
* tib:                                   The Text Interpreter.
                                                            (line  8759)
* tick ('):                              Execution token.   (line  8103)
* TILE performance:                      Performance.       (line 18819)
* time&date:                             Keeping track of Time.
                                                            (line 16562)
* time-related words:                    Keeping track of Time.
                                                            (line 16558)
* TMP, TEMP - environment variable:      Environment variables.
                                                            (line   815)
* TO:                                    Values.            (line  6893)
* TO on non-VALUEs:                      core-ambcond.      (line 17152)
* TO on non-VALUEs and non-locals:       locals-ambcond.    (line 17532)
* to-method::                            User-defined TO and DEFER@.
                                                            (line  7529)
* to-table::                             User-defined TO and DEFER@.
                                                            (line  7525)
* to-this:                               Objects Glossary.  (line 13247)
* tokens for words:                      Tokens for Words.  (line  8082)
* TOS definition:                        Stacks and Postfix notation.
                                                            (line  2940)
* TOS optimization for primitives:       TOS Optimization.  (line 18749)
* touchdown:                             actor methods.     (line 19043)
* touchup:                               actor methods.     (line 19046)
* toupper:                               Characters.        (line  5274)
* translate-dnum:                        Dealing with existing Recognizers.
                                                            (line  9196)
* translate-method::                     Dealing with existing Recognizers.
                                                            (line  9215)
* translate-nt:                          Dealing with existing Recognizers.
                                                            (line  9190)
* translate-num:                         Dealing with existing Recognizers.
                                                            (line  9193)
* translate-state:                       Dealing with existing Recognizers.
                                                            (line  9220)
* translate::                            Dealing with existing Recognizers.
                                                            (line  9186)
* traverse-wordlist:                     Name token.        (line  8233)
* trigonometric operations:              Floating Point.    (line  4405)
* true:                                  Boolean Flags.     (line  3762)
* truncation of floating-point numbers:  floating-idef.     (line 17423)
* try:                                   Exception Handling.
                                                            (line  6544)
* try-recognize:                         Dealing with existing Recognizers.
                                                            (line  9199)
* tt:                                    Locating exception source.
                                                            (line 14101)
* tuck:                                  Data stack.        (line  4532)
* turnkey image files:                   Modifying the Startup Sequence.
                                                            (line 18319)
* Tutorial:                              Tutorial.          (line   947)
* type:                                  Displaying characters and strings.
                                                            (line 10782)
* types of locals:                       Gforth locals.     (line 11501)
* types of stack items:                  Notation.          (line  3659)
* types tutorial:                        Types Tutorial.    (line  1331)
* typewhite:                             Displaying characters and strings.
                                                            (line 10793)
* u*/:                                   Integer division.  (line  3965)
* u*/mod:                                Integer division.  (line  3980)
* U+DO:                                  Counted Loops.     (line  5990)
* u, stack item type:                    Notation.          (line  3671)
* U-DO:                                  Counted Loops.     (line  6011)
* u-[do:                                 Counted Loops.     (line  6003)
* u.:                                    Simple numeric output.
                                                            (line 10423)
* u.r:                                   Simple numeric output.
                                                            (line 10434)
* u/:                                    Integer division.  (line  3916)
* u/-stage1m:                            Two-stage integer division.
                                                            (line  4076)
* u/-stage2m:                            Two-stage integer division.
                                                            (line  4080)
* u/mod:                                 Integer division.  (line  3936)
* u/mod-stage2m:                         Two-stage integer division.
                                                            (line  4088)
* u<:                                    Numeric comparison.
                                                            (line  4256)
* u<=:                                   Numeric comparison.
                                                            (line  4258)
* u>:                                    Numeric comparison.
                                                            (line  4260)
* u>=:                                   Numeric comparison.
                                                            (line  4262)
* uallot:                                Task-local data.   (line 14747)
* ud, stack item type:                   Notation.          (line  3675)
* ud.:                                   Simple numeric output.
                                                            (line 10445)
* ud.r:                                  Simple numeric output.
                                                            (line 10454)
* ud/mod:                                Integer division.  (line  3986)
* UDefer:                                Task-local data.   (line 14755)
* ukeyed:                                actor methods.     (line 19049)
* um*:                                   Mixed precision.   (line  3866)
* um/mod:                                Integer division.  (line  3950)
* umax:                                  Single precision.  (line  3823)
* umin:                                  Single precision.  (line  3821)
* umod:                                  Integer division.  (line  3925)
* umod-stage2m:                          Two-stage integer division.
                                                            (line  4084)
* unaligned memory access:               Special Memory Accesses.
                                                            (line  4921)
* uncolored-mode:                        Terminal output.   (line 10868)
* undefined word:                        core-ambcond.      (line 16998)
* undefined word, ', POSTPONE, ['], [COMPILE]: core-ambcond.
                                                            (line 17157)
* under+:                                Single precision.  (line  3804)
* unescape:                              Substitute.        (line 11372)
* unexpected end of the input buffer:    core-ambcond.      (line 17103)
* unlock:                                Semaphores.        (line 14791)
* unloop:                                Counted Loops.     (line  6064)
* unmapped block numbers:                file-ambcond.      (line 17401)
* UNREACHABLE:                           Where are locals visible by name?.
                                                            (line 11712)
* UNTIL:                                 Arbitrary control structures.
                                                            (line  6243)
* UNTIL loop:                            Simple Loops.      (line  5792)
* unused:                                Dictionary allocation.
                                                            (line  4717)
* unused-words:                          Locating uses of a word.
                                                            (line 14095)
* unwind-protect:                        Exception Handling.
                                                            (line  6563)
* up@:                                   Task-local data.   (line 14761)
* update:                                Blocks.            (line 10353)
* UPDATE, no current block buffer:       block-ambcond.     (line 17252)
* updated?:                              Blocks.            (line 10356)
* upper and lower case:                  Case insensitivity.
                                                            (line  3705)
* use:                                   Blocks.            (line 10307)
* User:                                  Task-local data.   (line 14738)
* user input device, method of selecting: core-idef.        (line 16903)
* user output device, method of selecting: core-idef.       (line 16908)
* user space:                            Task-local data.   (line 14732)
* user variables:                        Task-local data.   (line 14732)
* user':                                 Task-local data.   (line 14765)
* user-defined defining words:           User-defined Defining Words.
                                                            (line  7101)
* Uses of a word:                        Locating uses of a word.
                                                            (line 14047)
* utime:                                 Keeping track of Time.
                                                            (line 16571)
* UValue:                                Task-local data.   (line 14751)
* v*:                                    Floating Point.    (line  4397)
* Value:                                 Values.            (line  6877)
* value-flavoured locals:                Gforth locals.     (line 11509)
* values:                                Values.            (line  6866)
* var:                                   Class Declaration. (line 13441)
* var <1>:                               Basic Mini-OOF Usage.
                                                            (line 13503)
* Variable:                              Variables.         (line  6771)
* variable-flavoured locals:             Gforth locals.     (line 11509)
* variables:                             Variables.         (line  6746)
* variadic C functions:                  Declaring C Functions.
                                                            (line 15042)
* Varue:                                 Varues.            (line  6907)
* varue-flavoured locals:                Gforth locals.     (line 11509)
* varues:                                Varues.            (line  6902)
* versions, invoking other versions of Gforth: Invoking Gforth.
                                                            (line   661)
* vglue:                                 widget methods.    (line 19157)
* vglue@:                                widget methods.    (line 19166)
* view (called locate in Gforth):        Locating source code definitions.
                                                            (line 13976)
* viewing the documentation of a word in Emacs: Emacs and Gforth.
                                                            (line 17830)
* viewing the source of a word in Emacs: Emacs Tags.        (line 17858)
* virtual function:                      Object-Oriented Terminology.
                                                            (line 12574)
* virtual function table:                Objects Implementation.
                                                            (line 12989)
* virtual machine:                       Engine.            (line 18361)
* virtual machine instructions, implementation: Primitives. (line 18667)
* visibility of locals:                  Where are locals visible by name?.
                                                            (line 11669)
* vlist:                                 Word Lists.        (line  9452)
* Vocabularies, detailed explanation:    Vocabularies.      (line  9495)
* Vocabulary:                            Word Lists.        (line  9469)
* vocs:                                  Word Lists.        (line  9478)
* vocstack empty, previous:              search-ambcond.    (line 17625)
* vocstack full, also:                   search-ambcond.    (line 17628)
* vp-bottom:                             widget methods.    (line 19264)
* vp-left:                               widget methods.    (line 19267)
* vp-needed:                             widget methods.    (line 19276)
* vp-reslide:                            widget methods.    (line 19273)
* vp-right:                              widget methods.    (line 19270)
* vp-top:                                widget methods.    (line 19261)
* w:                                     widget methods.    (line 19103)
* w!:                                    Special Memory Accesses.
                                                            (line  4954)
* w,:                                    Dictionary allocation.
                                                            (line  4745)
* w, stack item type:                    Notation.          (line  3667)
* w-color:                               widget methods.    (line 19136)
* w/o:                                   General files.     (line  9901)
* W::                                    Locals definition words.
                                                            (line 11619)
* w>s:                                   Special Memory Accesses.
                                                            (line  5018)
* w@:                                    Special Memory Accesses.
                                                            (line  4951)
* WA::                                   Locals definition words.
                                                            (line 11622)
* walign:                                Address arithmetic.
                                                            (line  5159)
* waligned:                              Address arithmetic.
                                                            (line  5156)
* WARNING":                              Exception Handling.
                                                            (line  6671)
* warning-color:                         Terminal output.   (line 10841)
* warnings:                              Exception Handling.
                                                            (line  6674)
* wbe:                                   Special Memory Accesses.
                                                            (line  4980)
* wfield::                               Forth200x Structures.
                                                            (line 12513)
* where:                                 Locating uses of a word.
                                                            (line 14047)
* where to go next:                      Where to go next.  (line  3412)
* whereg:                                Locating uses of a word.
                                                            (line 14076)
* WHILE:                                 Arbitrary control structures.
                                                            (line  6273)
* WHILE loop:                            Simple Loops.      (line  5781)
* wid:                                   Word Lists.        (line  9342)
* wid, stack item type:                  Notation.          (line  3692)
* widget:                                MINOS2 object framework.
                                                            (line 19022)
* Win32Forth performance:                Performance.       (line 18819)
* wior type description:                 Notation.          (line  3694)
* wior values and meaning:               file-idef.         (line 17355)
* within:                                Numeric comparison.
                                                            (line  4264)
* wle:                                   Special Memory Accesses.
                                                            (line  4984)
* word:                                  Introducing the Text Interpreter.
                                                            (line  2838)
* word <1>:                              The Input Stream.  (line  9281)
* WORD buffer size:                      core-idef.         (line 16935)
* word glossary entry format:            Notation.          (line  3587)
* word list for defining locals:         Locals implementation.
                                                            (line 11964)
* word lists:                            Word Lists.        (line  9330)
* word lists - example:                  Word list example. (line  9578)
* word lists - why use them?:            Why use word lists?.
                                                            (line  9530)
* word name too long:                    core-ambcond.      (line 17001)
* WORD, string overflow:                 core-ambcond.      (line 17169)
* wordlist:                              Word Lists.        (line  9382)
* wordlist-words:                        Word Lists.        (line  9455)
* wordlists:                             Environmental Queries.
                                                            (line  9663)
* wordlists tutorial:                    Wordlists and Search Order Tutorial.
                                                            (line  2700)
* words:                                 Words.             (line  3584)
* words <1>:                             Word Lists.        (line  9448)
* words used in your program:            Standard Report.   (line 16671)
* words, forgetting:                     Forgetting words.  (line 14289)
* wordset:                               Notation.          (line  3622)
* wrap-xt:                               Deferred Words.    (line  7879)
* write-file:                            General files.     (line  9958)
* write-line:                            General files.     (line  9960)
* wrol:                                  Bitwise operations.
                                                            (line  4198)
* wror:                                  Bitwise operations.
                                                            (line  4202)
* WTF??:                                 Debugging.         (line 14377)
* ww:                                    Locating uses of a word.
                                                            (line 14053)
* W^:                                    Locals definition words.
                                                            (line 11625)
* x:                                     widget methods.    (line 19097)
* x!:                                    Special Memory Accesses.
                                                            (line  4966)
* x,:                                    Dictionary allocation.
                                                            (line  4749)
* x-size:                                Xchars and Unicode.
                                                            (line 11202)
* x-width:                               Xchars and Unicode.
                                                            (line 11256)
* x>s:                                   Special Memory Accesses.
                                                            (line  5024)
* x@:                                    Special Memory Accesses.
                                                            (line  4963)
* xalign:                                Address arithmetic.
                                                            (line  5171)
* xaligned:                              Address arithmetic.
                                                            (line  5168)
* xbe:                                   Special Memory Accesses.
                                                            (line  4996)
* xc!+:                                  Xchars and Unicode.
                                                            (line 11225)
* xc!+?:                                 Xchars and Unicode.
                                                            (line 11217)
* xc,:                                   Xchars and Unicode.
                                                            (line 11273)
* xc-size:                               Xchars and Unicode.
                                                            (line 11199)
* xc-width:                              Xchars and Unicode.
                                                            (line 11266)
* xc@:                                   Xchars and Unicode.
                                                            (line 11206)
* xc@+:                                  Xchars and Unicode.
                                                            (line 11209)
* xc@+?:                                 Xchars and Unicode.
                                                            (line 11213)
* xchar+:                                Xchars and Unicode.
                                                            (line 11232)
* xchar-:                                Xchars and Unicode.
                                                            (line 11236)
* XCHAR-ENCODING:                        Environmental Queries.
                                                            (line  9670)
* XCHAR-MAXMEM:                          Environmental Queries.
                                                            (line  9680)
* xd!:                                   Special Memory Accesses.
                                                            (line  4972)
* xd,:                                   Dictionary allocation.
                                                            (line  4751)
* xd>s:                                  Special Memory Accesses.
                                                            (line  5027)
* xd@:                                   Special Memory Accesses.
                                                            (line  4969)
* xdbe:                                  Special Memory Accesses.
                                                            (line  5004)
* xdle:                                  Special Memory Accesses.
                                                            (line  5008)
* xemit:                                 Displaying characters and strings.
                                                            (line 10786)
* xfield::                               Forth200x Structures.
                                                            (line 12519)
* xhold:                                 Xchars and Unicode.
                                                            (line 11269)
* xkey:                                  Xchars and Unicode.
                                                            (line 11262)
* xkey?:                                 Single-key input.  (line 10893)
* xle:                                   Special Memory Accesses.
                                                            (line  5000)
* xor:                                   Bitwise operations.
                                                            (line  4133)
* xt:                                    Introducing the Text Interpreter.
                                                            (line  2838)
* xt <1>:                                Execution token.   (line  8088)
* xt input format:                       Literals in source code.
                                                            (line  3563)
* XT tutorial:                           Execution Tokens Tutorial.
                                                            (line  2272)
* xt, stack item type:                   Notation.          (line  3690)
* xt-new:                                Objects Glossary.  (line 13250)
* xt-see:                                Examining compiled code.
                                                            (line 14121)
* xt-see-code:                           Examining compiled code.
                                                            (line 14145)
* xt-simple-see:                         Examining compiled code.
                                                            (line 14128)
* XT::                                   Locals definition words.
                                                            (line 11655)
* xt>name:                               Name token.        (line  8227)
* XTA::                                  Locals definition words.
                                                            (line 11658)
* xywh:                                  widget methods.    (line 19169)
* xywhd:                                 widget methods.    (line 19172)
* x\string-:                             Xchars and Unicode.
                                                            (line 11245)
* y:                                     widget methods.    (line 19100)
* zero-length string as a name:          core-ambcond.      (line 17103)
* Zsoter's object-oriented model:        Comparison with other object models.
                                                            (line 13742)

