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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>&#92;begin{<b class='environment'>productionlist</b>}</tt>
    <tt>[</tt><var>language</var><tt>]</tt>
<br /><tt>&#92;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'>&#92;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'>&#92;token</tt> macros and any additional content
      needed to describe the grammatical model of <var>symbol</var>.  Only
      one <tt class='macro'>&#92;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'>&#92;token</tt></b>
    <tt>{</tt><var>name</var><tt>}</tt></dt>
<dd>
      The name of a symbol defined by a <tt class='macro'>&#92;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'>&#92;productionlist</tt> environment; any number of
    groupings may be used to describe the grammar.  Every use of the
    <tt class='macro'>&#92;token</tt> must correspond to a <tt class='macro'>&#92;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 2.4.2, documentation updated on 28 September 2005.</span>
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