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<title>6.12 Grammar Production Displays </title>
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<H2><A NAME="SECTION0007120000000000000000"></A><A NAME="grammar-displays"></A>
<BR>
6.12 Grammar Production Displays
</H2>
<P>
Special markup is available for displaying the productions of a
formal grammar. The markup is simple and does not attempt to
model all aspects of BNF (or any derived forms), but provides
enough to allow context-free grammars to be displayed in a way
that causes uses of a symbol to be rendered as hyperlinks to the
definition of the symbol. There is one environment and a pair of
macros:
<P>
<dl class='envdesc'>
<dt><tt>\begin{<b class='environment'>productionlist</b>}</tt>
<tt>[</tt><var>language</var><tt>]</tt>
<br /><tt>\end{<b class='environment'>productionlist</b>}</tt></dt>
<dd>
This environment is used to enclose a group of productions. The
two macros are only defined within this environment. If a
document describes more than one language, the optional parameter
<var>language</var> should be used to distinguish productions between
languages. The value of the parameter should be a short name
that can be used as part of a filename; colons or other
characters that can't be used in filename across platforms
should be included.
</dd></dl>
<P>
<dl class='macrodesc'>
<dt><b><tt class='macro'>\production</tt></b>
<tt>{</tt><var>name</var><tt>}</tt><tt>{</tt><var>definition</var><tt>}</tt></dt>
<dd>
A production rule in the grammar. The rule defines the symbol
<var>name</var> to be <var>definition</var>. <var>name</var> should not
contain any markup, and the use of hyphens in a document which
supports more than one grammar is undefined. <var>definition</var>
may contain <tt class='macro'>\token</tt> macros and any additional content
needed to describe the grammatical model of <var>symbol</var>. Only
one <tt class='macro'>\production</tt> may be used to define a symbol --
multiple definitions are not allowed.
</dd></dl>
<P>
<dl class='macrodesc'>
<dt><b><tt class='macro'>\token</tt></b>
<tt>{</tt><var>name</var><tt>}</tt></dt>
<dd>
The name of a symbol defined by a <tt class='macro'>\production</tt> macro, used
in the <var>definition</var> of a symbol. Where possible, this will
be rendered as a hyperlink to the definition of the symbol
<var>name</var>.
</dd></dl>
<P>
Note that the entire grammar does not need to be defined in a
single <tt class='environment'>\productionlist</tt> environment; any number of
groupings may be used to describe the grammar. Every use of the
<tt class='macro'>\token</tt> must correspond to a <tt class='macro'>\production</tt>.
<P>
The following is an example taken from the
<em class="citetitle"><a
href="../ref/identifiers.html"
title="Python Reference Manual"
>Python Reference Manual</a></em>:
<P>
<div class="verbatim"><pre>
\begin{productionlist}
\production{identifier}
{(\token{letter}|"_") (\token{letter} | \token{digit} | "_")*}
\production{letter}
{\token{lowercase} | \token{uppercase}}
\production{lowercase}
{"a"..."z"}
\production{uppercase}
{"A"..."Z"}
\production{digit}
{"0"..."9"}
\end{productionlist}
</pre></div>
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<span class="release-info">Release 2.4.3, documentation updated on 29 March 2006.</span>
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