117 lines
3.9 KiB
HTML
117 lines
3.9 KiB
HTML
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<head>
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<!-- This file has been generated by unroff 1.0, 03/21/96 19:29:45. -->
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<!-- Do not edit! -->
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<link rev="made" href="mailto:net@informatik.uni-bremen.de">
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<title>unroff Programmer's Manual, section 10.</title>
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</head><body>
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<h2><a name="section10">10.</a> <tt> </tt>Input and Output Primitives
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</h2>
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<p>
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 <tt> </tt> <tt> </tt> <tt> </tt><i>unroff
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</i>provides one new input primitive and one new output primitive that
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work with the current input stream and current output stream (and a
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third primitive which is just an optimization of the latter, as
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well as a few auxiliary functions).<tt> </tt>
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<h2>
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(emit <i>.</i> <i>args</i>)
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</h2>
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<p>
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 <tt> </tt> <tt> </tt> <tt> </tt><i>emit
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</i>is the only stream-based output primitive.<tt> </tt>
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It receives any number of strings, symbols, and characters,
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concatenates its arguments, and sends the resulting string to
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the current output stream (to standard output if the the current
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output stream has been assigned #f).<tt> </tt>
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<i>emit
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</i>is primarily used in situations where text has to
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be output without rescanning it and without applying any
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character translations.<tt> </tt>
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It is also used from within the event procedures that are called
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for their side-effects, for example, by the
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<i>prolog
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</i>and
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<i>epilog
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</i>event procedures to generate a header and trailer for each
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output file.<tt> </tt>
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The primitive returns the empty symbol so that it can be called
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as the last form in an event procedure whose result is used.<tt> </tt>
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<p>
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 <tt> </tt> <tt> </tt> <tt> </tt>Example:
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the new troff request for transparent output, as explained in the
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<a href="./unroff.1.html">manual page</a>
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<i>unroff</i>(1),
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can be implement like this:
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<dl><dt><dd>
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<pre>
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(defrequest '>>
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(lambda (>> code)
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(emit code #\newline)))
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</pre>
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</dl>
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<h2>
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(read-line)
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</h2>
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<p>
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 <tt> </tt> <tt> </tt> <tt> </tt>This primitive reads the next input line from the current input
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stream and returns it as a string.<tt> </tt>
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An error is signaled if the current input stream has been bound
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to #f, which is the case, for example, when
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<i>unroff
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</i>has been called with the option
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<b>-t
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</b>to start an interactive top level.<tt> </tt>
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If an incomplete last line (i.e. a line without a terminating
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newline) is returned by the target pointed to by the current
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input stream, a newline is appended.<tt> </tt>
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Thus,
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<i>read-line
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</i>always returns at least a string containing a newline character.<tt> </tt>
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<h2>
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(read-line-expand)
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</h2>
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<p>
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 <tt> </tt> <tt> </tt> <tt> </tt>This primitive is nothing more than an optimization for
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<dl><dt><dd>
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<pre>
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(parse-expand (read-line))
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</pre>
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</dl>
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which has been provided to speed up frequently used functions like
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macro expansion.<tt> </tt>
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<h2>
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(unread-line <i>string</i>)
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</h2>
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<p>
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 <tt> </tt> <tt> </tt> <tt> </tt>This primitive pushes back an input line to the current input
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stream, which will then be returned by the next call to
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<i>read-line
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</i>or
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<i>read-line-expand</i>,
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or it will be read by the parser in the normal way when processing
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the current input file.<tt> </tt>
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<i>string
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</i>need not have a terminating newline.<tt> </tt>
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Strings pushed back by multiple calls to
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<i>unread-line
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</i>are coalesced and returned as a whole by the next input operation.<tt> </tt>
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<h2>
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(error-port)
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</h2>
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<p>
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 <tt> </tt> <tt> </tt> <tt> </tt>Returns a Scheme output port that is bound to the program's
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standard error output.<tt> </tt>
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This primitive is used by the default Scheme error handler provided
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by
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<i>unroff
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</i>and by the
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<i>warn
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</i>utility function<a href="m-notes.html#footnote4">[note 4]</a>
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.<tt> </tt>
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Note that
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<i>error-port
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</i>returns an ordinary Scheme port, not a stream.<tt> </tt>
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<p><hr>
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Markup created by <em>unroff</em> 1.0, <tt> </tt> <tt> </tt>March 21, 1996, <tt> </tt> <tt> </tt>net@informatik.uni-bremen.de</body>
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</html>
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