### NAME

Tcl_CreateMathFunc - Define a new math function for expressions

### SYNOPSIS

#include <tcl.h>
Tcl_CreateMathFunc(interp, name, numArgs, argTypes, proc, clientData)

### ARGUMENTS

Tcl_Interp *interp (in)
  Interpreter in which new function will be defined.

char *name (in)
  Name for new function.

int numArgs (in)
  Number of arguments to new function; also gives size of argTypes array.

Tcl_ValueType *argTypes (in)
  Points to an array giving the permissible types for each argument to function.

Tcl_MathProc *proc (in)
  Procedure that implements the function.

ClientData clientData (in)
  Arbitrary one-word value to pass to proc when it is invoked.

### DESCRIPTION

Tcl allows a number of mathematical functions to be used in expressions, such as sin, cos, and hypot. Tcl_CreateMathFunc allows applications to add additional functions to those already provided by Tcl or to replace existing functions. Name is the name of the function as it will appear in expressions. If name doesn't already exist as a function then a new function is created. If it does exist, then the existing function is replaced. NumArgs and argTypes describe the arguments to the function. Each entry in the argTypes array must be either TCL_INT, TCL_DOUBLE, or TCL_EITHER to indicate whether the corresponding argument must be an integer, a double-precision floating value, or either, respectively.

Whenever the function is invoked in an expression Tcl will invoke proc. Proc should have arguments and result that match the type Tcl_MathProc:

    typedef int Tcl_MathProc(
    	ClientData clientData,
    	Tcl_Interp *interp,
    	Tcl_Value *args,
    	Tcl_Value *resultPtr);

When proc is invoked the clientData and interp arguments will be the same as those passed to Tcl_CreateMathFunc. Args will point to an array of numArgs Tcl_Value structures, which describe the actual arguments to the function:

    typedef struct Tcl_Value {
    	Tcl_ValueType type;
    	long intValue;
    	double doubleValue;
    } Tcl_Value;

The type field indicates the type of the argument and is either TCL_INT or TCL_DOUBLE. It will match the argTypes value specified for the function unless the argTypes value was TCL_EITHER. Tcl converts the argument supplied in the expression to the type requested in argTypes, if that is necessary. Depending on the value of the type field, the intValue or doubleValue field will contain the actual value of the argument.

Proc should compute its result and store it either as an integer in resultPtr->intValue or as a floating value in resultPtr->doubleValue. It should set also resultPtr->type to either TCL_INT or TCL_DOUBLE to indicate which value was set. Under normal circumstances proc should return TCL_OK. If an error occurs while executing the function, proc should return TCL_ERROR and leave an error message in interp->result.

### KEYWORDS

expression, mathematical function

    Copyright © 1989-1993 The Regents of the University of California.
    Copyright © 1994-1996 Sun Microsystems, Inc.
    Copyright © 1995-1997 Roger E. Critchlow Jr.