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<Section id="section.api.interfaces">
  <Title/Compiler Interfaces/
  <P>
    As said above, compiler engines are narrators.  The term <Q/compiler
    interface/ simply denotes a standard listener attached to a compiler
    engine.  This section presents what is required to implement a compiler
    interface.
  <P>
    First the notifications sent by compiler engines are documented.  These
    include normal compiler output and information about compiler state
    changes.  Then a specific compiler interface is described that makes
    many compilation tasks easy to control.
  <SubSection>
    <Title/Sent Notifications/
    <Para class=apropos><Title/Query Queue/
      <List>
	<Entry><<newQuery(?_{I} ?_{T})>>
	<Item>
	  A new query&nbsp;?_{T} with identification&nbsp;?_{I} has been
	  enqueued.
	<Entry><<runQuery(?_{I} ?_{T})>>
	<Item>
	  The query&nbsp;?_{T} with identification&nbsp?_{I} is now being
	  executed.
	<Entry><<removeQuery(?_{I})>>
	<Item>
	  The query with identification&nbsp;?_{I} has been removed from
	  the query queue, either because it finished executing or because
	  it was dequeued by a user program.
      </List>
    <Para class=apropos><Title/Compiler Activity/
      <List>
	<Entry><<busy()>>
	<Item>
	  The compiler is currently busy (&ie;, executing a query).
	<Entry><<idle()>>
	<Item>
	  The compiler is currently idle (&ie;, waiting for a query to
	  be enqueued).
      </List>
    <Para class=apropos><Title/State Change/
      <List>
	<Entry><<switch(?_{SwitchName} ?_{B})>>
	<Item>
	  The given switch has been set to&nbsp;?_{B}.
	<Entry><<switches(?_{R})>>
	<Item>
	  The settings of all switches is transmitted as a record mapping
	  each switch name to its setting.
	<Entry><<maxNumberOfErrors(?_{I})>>
	<Item>
	  The maximum number of errors after which to abort compilation
	  has been set to&nbsp;?_{I}.
	<Entry><<baseURL(?_{AU})>>
	<Item>
	  The base URL relative to which the <<require>> clause of computed
	  functors is resolved has been set to ?_{AU}.
	<Entry><<env(?_{Env})>>
	<Item>
	  The environment has been set to ?_{Env}.
      </List>
    <Para class=apropos><Title/Output/
      <List>
	<Entry><<info(?_{V})>>
	<Item>
	  An information message&nbsp;?_{V} is to be printed out.
	<Entry><<info(?_{V} ?_{Coord})>>
	<Item>
	  An information message&nbsp;?_{V}, related to the source coordinates
	  ?_{Coord}, is to be printed out.
	<Entry><<message(?_{R} ?_{Coord})>>
	<Item>
	  An error or warning message&nbsp;?_{R}, related to the source
	  coordinates ?_{Coord}, is to be printed out.  ?_{R}&nbsp;has
	  the standard error message format, described in <Ptr.Extern
	  to="ozdoc:system" key="chapter.error">.
	<Entry><<insert(?_{V} ?_{Coord})>>
	<Item>
	  During parsing, the file named&nbsp;?_{V} has been read.
	  The corresponding <<\insert>> directive (if any) was at source
	  coordinates ?_{Coord}.
	<Entry><<displaySource(?_{TitleV} ?_{ExtV} ?_{V})>>
	<Item>
	  A source text&nbsp;?_{V} with title&nbsp;?_{TitleV} is to be
	  displayed; its format is the one for which the file extension
	  ?_{ExtV} is typically used (such as <File/oz/ or <File/ozm/).
	<Entry><<attention()>>
	<Item>
	  The error output buffer should be raised with the cursor at
	  the current output coordinates (an error message should follow).
      </List>
    <Para class=apropos><Title/Synchronization/
      <List>
	<Entry><<pong(?_{X})>>
	<Item>
	  This is sent in response to a <<ping(_)>> or <<ping(_ ?_{X})>> query
	  (see <Ptr to="section.api.engines">).  In the first case, <<unit>>
	  is returned in&nbsp;?_{X}.
      </List>
  <SubSection>
    <Title/The <<Compiler.interface>> Class/
    <P>
      The <<Compiler.interface>> class is a subclass of the error listener
      class described in <Ptr to="appendix.narrator">.  Its purpose is
      to provide a standard listener powerful enough to server many
      purposes, to spare the user of defining an own listener.
    <Para class=apropos><Title/Methods/
      In addition to the standard error listener interface, it supports the
      following methods.
      <List>
	<Entry><<init(?+{EngineO} ?+{VerboseL} &lt;= false)>>
	<Item>
	  initializes a new compiler interface, attaching it to the
	  compiler engine ?_{EngineO}.  ?_{VerboseL} can be one of <<true>>,
	  <<false>>, or <<auto>>:  If <<true>>, all messages, including the
	  compiler's banner, will be output.  If <<false>>, no messages
	  will be output.  If <<auto>>, the interface will remain silent
	  unless an error of warning message arrives, in which case it
	  will become verbose.
	<Entry><<sync()>>
	<Item>
	  waits until the compiler engine becomes idle.
	<Entry><<getInsertedFiles(??{Vs})>>
	<Item>
	  returns a list of the file names that compilation has caused
	  the inclusion of so far, in order of appearance.
	<Entry><<getSource(??{V})>>
	<Item>
	  returns the source that has last been displayed by the
	  compiler (typically some intermediate representation), or
	  the empty string if none.
	<Entry><<reset()>>
	<Item>
	  clears the internal lists of inserted files and the displayed
	  source.
	<Entry><<clear()>>
	<Item>
	  is the same as <<reset>>.
      </List>
</Section>
