176 lines
6.5 KiB
HTML
176 lines
6.5 KiB
HTML
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<html>
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<head>
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<!-- This file has been generated by unroff 1.0, 03/21/96 19:29:44. -->
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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 8.</title>
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</head><body>
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<h2><a name="section8">8.</a> <tt> </tt>Calling the Parser
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</h2>
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<p>
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 <tt> </tt> <tt> </tt> <tt> </tt>The following Scheme primitives are used by event procedures for
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requests, macros, and escape characters to parse their arguments
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or to parse lines of text that have been read from an input source.<tt> </tt>
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Each of the primitives can be invoked with zero or more arguments
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of type string, symbol, or character.<tt> </tt>
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The arguments are concatenated to form a Scheme string which is then
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passed to the parser, and the result is returned as a new string.<tt> </tt>
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<h2>
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<a name=".parse">(parse <i>.</i> <i>args</i>)</a></h2>
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<p>
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 <tt> </tt> <tt> </tt> <tt> </tt>This primitive feeds its arguments to the ``escape parsing''
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pass as described in the previous section.<tt> </tt>
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It scans its arguments for special characters and escape
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sequences and replaces them by the corresponding event values
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(or results), and it executes character translations.<tt> </tt>
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<h2>
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<a name=".translate">(translate <i>.</i> <i>args</i>)</a></h2>
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<p>
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 <tt> </tt> <tt> </tt> <tt> </tt>Like
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<i>parse
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</i>above, except that only output character translations (defined by calls to
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<i>defchar</i>)
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are executed.<tt> </tt>
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<h2>
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(parse-expand <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>This primitive applies the ``expansion parsing'' phase (as described in the
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previous section) to its arguments.<tt> </tt>
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Compared to
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<i>parse</i>,
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<i>parse-expand
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</i>is only used rarely, as input lines read in the normal way are
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scanned for string and number register references anyway.<tt> </tt>
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The sample implementation supplied by
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<i>unroff
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</i>for the requests ``.ds'', ``.as'', and '\*' makes use of this primitive
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to rescan the contents of user-defined strings upon interpolation.<tt> </tt>
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<h2>
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(parse-line <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>This primitive parses an entire input line, which may contain a call
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to a request or macro, as described in the previous section.<tt> </tt>
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The line made up by the primitive's arguments is treated exactly as
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it if were read from an input file, although it need not have a
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terminating newline.<tt> </tt>
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Two places where this primitive is required are the handler for
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the request ``.so'' and the code that expands user-defined macros.<tt> </tt>
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<h2>
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(parse-copy-mode <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>The primitive
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<i>parse-copy-mode
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</i>parses its arguments in a manner similar to troff ``copy mode''.<tt> </tt>
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In this mode, escape sequences beginning with '\$' are dealt
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with (by calling their event procedures), the sequence `\\'
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is replaced by a single `\', and each occurrence of `\.'
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is replaced by a period.<tt> </tt>
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Macro bodies are parsed in copy mode during macro definition and again
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when the macros are expanded.<tt> </tt>
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<p>
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 <tt> </tt> <tt> </tt> <tt> </tt>The sample implementation of user-defined macros supplied by
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<i>unroff
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</i>defines suitable event handlers for the usual
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<dl><dt><dd>
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<pre>
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\$1 \$2 ...
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</pre>
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</dl>
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escape sequences (there is no limit to the number of arguments,
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and the groff long name convention may be used to denote an
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argument number), and in addition for the groff extensions
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<dl><dt><dd>
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<pre>
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\$0 \$* \$@
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</pre>
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</dl>
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as explained in the
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<a href="./unroff.1.html">manual page</a>
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<i>unroff</i>(1).<tt> </tt>
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<h2>
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(parse-expression <i>expr</i> <i>fail</i> <i>scale</i>)
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<br>
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(parse-expression-rest <i>expr</i> <i>fail</i> <i>scale</i>)
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</h2>
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<p>
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 <tt> </tt> <tt> </tt> <tt> </tt>These primitives evaluate the numeric expression specified by
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the string argument
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<i>expr
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</i>and return the result as an exact number.<tt> </tt>
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The usual troff expression syntax, operators, and scale
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indicators are supported.<tt> </tt>
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If an error occurs during evaluation (for instance, if
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<i>expr
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</i>is not a syntactically valid expression),
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a warning message is displayed and
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<i>fail
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</i>(which may be an arbitrary Scheme object) is returned.<tt> </tt>
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The character argument
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<i>scale
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</i>is the default scale indicator, for example `#\m', or `#\u'
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for basic units.<tt> </tt>
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<p>
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 <tt> </tt> <tt> </tt> <tt> </tt>The primitive
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<i>parse-expression-rest
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</i>is identical to
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<i>parse-expression</i>,
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except that its return value is a cons cell whose car consists
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of the result of the evaluation and whose cdr is the rest of
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<i>expr
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</i>starting at the character position where parsing of the
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expression stopped.<tt> </tt>
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In other words, the primitive evaluates the portion of
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<i>expr
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</i>that constitutes a valid expression, and it returns the result
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and whatever is left over.<tt> </tt>
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Warning messages are also suppressed, except if an overflow occurs
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during evaluation.<tt> </tt>
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<i>parse-expression-rest
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</i>is useful for tasks like parsing the argument of the escape
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sequences `\l' and `\L' where an expression is immediately
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followed by another character.<tt> </tt>
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Examples:
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<dl><dt><dd>
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<pre>
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(parse-expression "(2+8)/5" 0 #\u) => 2
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(parse-expression "foo" #f #\u) => #f; prints warning
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(parse-expression-rest "1+1" #f #\u) => (2 . "")
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(parse-expression-rest "(2+8)/5foo" 0 #\u) => (2 . "foo")
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(parse-expression-rest "15\&-" 0 #\u) => (15 . "\&-")
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</pre>
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</dl>
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<h2>
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(char-expression-delimiter? <i>char</i>)
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</h2>
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<p>
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 <tt> </tt> <tt> </tt> <tt> </tt>Returns #t if the character argument
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<i>char
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</i>is valid as the first character of a numeric expression (e.g. a digit),
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otherwise #f.<tt> </tt>
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<h2>
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(set-scaling! <i>scale</i> <i>factor</i> <i>divisor</i>)
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<br>
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(get-scaling <i>scale</i>)
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</h2>
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<p>
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 <tt> </tt> <tt> </tt> <tt> </tt>These primitives set and read the scale factor and divisor for
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the specified scale indicator.<tt> </tt>
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<i>scale
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</i>is the scale indicator (a character);
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<i>factor
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</i>and
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<i>divisor
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</i>are integers.<tt> </tt>
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<i>get-scaling
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</i>returns the scaling for the specified scale indicator as a pair
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of integers.<tt> </tt>
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The factors and divisors are initially set to 1 for all scale
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indicators; they must be assigned useful values by each back-end.<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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