<html> <head> <meta http-equiv="Content-Type" content="text/html; charset=US-ASCII"> <title>Nonterminal</title> <link rel="stylesheet" href="../../../../../../../../doc/src/boostbook.css" type="text/css"> <meta name="generator" content="DocBook XSL Stylesheets V1.75.0"> <link rel="home" href="../../../../index.html" title="Spirit 2.4"> <link rel="up" href="../generator_concepts.html" title="Generator Concepts"> <link rel="prev" href="narygenerator.html" title="NaryGenerator"> <link rel="next" href="../karma_basics.html" title="Basics"> </head> <body bgcolor="white" text="black" link="#0000FF" vlink="#840084" alink="#0000FF"> <table cellpadding="2" width="100%"><tr> <td valign="top"><img alt="Boost C++ Libraries" width="277" height="86" src="../../../../../../../../boost.png"></td> <td align="center"><a href="../../../../../../../../index.html">Home</a></td> <td align="center"><a href="../../../../../../../../libs/libraries.htm">Libraries</a></td> <td align="center"><a href="http://www.boost.org/users/people.html">People</a></td> <td align="center"><a href="http://www.boost.org/users/faq.html">FAQ</a></td> <td align="center"><a href="../../../../../../../../more/index.htm">More</a></td> </tr></table> <hr> <div class="spirit-nav"> <a accesskey="p" href="narygenerator.html"><img src="../../../../../../../../doc/src/images/prev.png" alt="Prev"></a><a accesskey="u" href="../generator_concepts.html"><img src="../../../../../../../../doc/src/images/up.png" alt="Up"></a><a accesskey="h" href="../../../../index.html"><img src="../../../../../../../../doc/src/images/home.png" alt="Home"></a><a accesskey="n" href="../karma_basics.html"><img src="../../../../../../../../doc/src/images/next.png" alt="Next"></a> </div> <div class="section"> <div class="titlepage"><div><div><h5 class="title"> <a name="spirit.karma.reference.generator_concepts.nonterminal"></a><a class="link" href="nonterminal.html" title="Nonterminal">Nonterminal</a> </h5></div></div></div> <a name="spirit.karma.reference.generator_concepts.nonterminal.description"></a><h6> <a name="id1032448"></a> <a class="link" href="nonterminal.html#spirit.karma.reference.generator_concepts.nonterminal.description">Description</a> </h6> <p> A Nonterminal is a symbol in a <a class="link" href="../../../abstracts/parsing_expression_grammar.html" title="Parsing Expression Grammar">Parsing Expression Grammar</a> production that represents a grammar fragment. Nonterminals may self reference to specify recursion. This is one of the most important concepts and the reason behind the word "recursive" in recursive descent generation. </p> <a name="spirit.karma.reference.generator_concepts.nonterminal.refinement_of"></a><h6> <a name="id1032470"></a> <a class="link" href="nonterminal.html#spirit.karma.reference.generator_concepts.nonterminal.refinement_of">Refinement of</a> </h6> <div class="blockquote"><blockquote class="blockquote"><p> <a class="link" href="generator.html" title="Generator"><code class="computeroutput"><span class="identifier">Generator</span></code></a> </p></blockquote></div> <a name="spirit.karma.reference.generator_concepts.nonterminal.signature"></a><h6> <a name="id1032502"></a> <a class="link" href="nonterminal.html#spirit.karma.reference.generator_concepts.nonterminal.signature">Signature</a> </h6> <p> Rules can have both consumed and inherited attributes. The rule's <span class="emphasis"><em>Signature</em></span> specifies both the consumed and inherited attributes. The specification uses the function declarator syntax: </p> <pre class="programlisting"><span class="identifier">RT</span><span class="special">(</span><span class="identifier">A0</span><span class="special">,</span> <span class="identifier">A1</span><span class="special">,</span> <span class="identifier">A2</span><span class="special">,</span> <span class="special">...,</span> <span class="identifier">AN</span><span class="special">)</span> </pre> <p> where <code class="computeroutput"><span class="identifier">RT</span></code> is the rule's consumed attribute and <code class="computeroutput"><span class="identifier">A0</span></code> ... <code class="computeroutput"><span class="identifier">AN</span></code> are the rule's inherited attributes. </p> <a name="spirit.karma.reference.generator_concepts.nonterminal.attributes"></a><h6> <a name="id1032601"></a> <a class="link" href="nonterminal.html#spirit.karma.reference.generator_concepts.nonterminal.attributes">Attributes</a> </h6> <p> The rule models a C++ function. The rule's consumed attribute is analogous to the function return value as it is the type -exposed- by the rule. Its inherited attributes are analogous to function arguments. The inherited attributes (arguments) can be passed in just like any <a class="link" href="../karma_basics.html#spirit.karma.reference.karma_basics.lazy_argument">Lazy Argument</a>, e.g.: </p> <pre class="programlisting"><span class="identifier">r</span><span class="special">(</span><span class="identifier">expr</span><span class="special">)</span> <span class="comment">// Evaluate expr at parse time and pass the result to the Nonterminal r </span></pre> <a name="spirit.karma.reference.generator_concepts.nonterminal._code__phrase_role__identifier___val__phrase___code_"></a><h6> <a name="id1032645"></a> <a class="link" href="nonterminal.html#spirit.karma.reference.generator_concepts.nonterminal._code__phrase_role__identifier___val__phrase___code_"><code class="computeroutput"><span class="identifier">_val</span></code></a> </h6> <p> The <code class="computeroutput"><span class="identifier">boost</span><span class="special">::</span><span class="identifier">spirit</span><span class="special">::</span><span class="identifier">karma</span><span class="special">::</span><span class="identifier">_val</span></code> placeholder can be used in <a href="../../../../../../phoenix/doc/html/index.html" target="_top">Phoenix</a> semantic actions anywhere in the Nonterminal's definition. This <a href="../../../../../../phoenix/doc/html/index.html" target="_top">Phoenix</a> placeholder refers to the Nonterminal's (consumed) attribute. The <code class="computeroutput"><span class="identifier">_val</span></code> placeholder acts like an immutable reference to the Nonterminal's attribute. </p> <a name="spirit.karma.reference.generator_concepts.nonterminal._code__phrase_role__identifier___r1__phrase___code_____code__phrase_role__identifier__r10__phrase___code_"></a><h6> <a name="id1032712"></a> <a class="link" href="nonterminal.html#spirit.karma.reference.generator_concepts.nonterminal._code__phrase_role__identifier___r1__phrase___code_____code__phrase_role__identifier__r10__phrase___code_"><code class="computeroutput"><span class="identifier">_r1</span></code>...<code class="computeroutput"><span class="identifier">r10</span></code></a> </h6> <p> The <code class="computeroutput"><span class="identifier">boost</span><span class="special">::</span><span class="identifier">spirit</span><span class="special">::</span><span class="identifier">_r1</span></code>...<code class="computeroutput"><span class="identifier">boost</span><span class="special">::</span><span class="identifier">spirit</span><span class="special">::</span><span class="identifier">r10</span></code> placeholders can be used in <a href="../../../../../../phoenix/doc/html/index.html" target="_top">Phoenix</a> semantic actions anywhere in the Nonterminal's definition. These <a href="../../../../../../phoenix/doc/html/index.html" target="_top">Phoenix</a> placeholders refer to the Nonterminal's inherited attributes. </p> <a name="spirit.karma.reference.generator_concepts.nonterminal.locals"></a><h6> <a name="id1032796"></a> <a class="link" href="nonterminal.html#spirit.karma.reference.generator_concepts.nonterminal.locals">Locals</a> </h6> <p> Nonterminals can have local variables that will be created on the stack at runtime. A locals descriptor added to the Nonterminal declaration will give the Nonterminal local variables: </p> <pre class="programlisting"><span class="keyword">template</span> <span class="special"><</span><span class="keyword">typename</span> <span class="identifier">T0</span><span class="special">,</span> <span class="keyword">typename</span> <span class="identifier">T1</span><span class="special">,</span> <span class="keyword">typename</span> <span class="identifier">T2</span><span class="special">,</span> <span class="special">...,</span> <span class="keyword">typename</span> <span class="identifier">TN</span><span class="special">></span> <span class="keyword">struct</span> <span class="identifier">locals</span><span class="special">;</span> </pre> <p> where <code class="computeroutput"><span class="identifier">T0</span></code> ... <code class="computeroutput"><span class="identifier">TN</span></code> are the types of local variables accessible in your <a href="../../../../../../phoenix/doc/html/index.html" target="_top">Phoenix</a> semantic actions using the placeholders: </p> <div class="itemizedlist"><ul class="itemizedlist" type="disc"> <li class="listitem"> <code class="computeroutput"><span class="identifier">boost</span><span class="special">::</span><span class="identifier">spirit</span><span class="special">::</span><span class="identifier">_a</span></code> </li> <li class="listitem"> <code class="computeroutput"><span class="identifier">boost</span><span class="special">::</span><span class="identifier">spirit</span><span class="special">::</span><span class="identifier">_b</span></code> </li> <li class="listitem"> <code class="computeroutput"><span class="identifier">boost</span><span class="special">::</span><span class="identifier">spirit</span><span class="special">::</span><span class="identifier">_c</span></code> </li> <li class="listitem"> <code class="computeroutput"><span class="identifier">boost</span><span class="special">::</span><span class="identifier">spirit</span><span class="special">::</span><span class="identifier">_d</span></code> </li> <li class="listitem"> <code class="computeroutput"><span class="identifier">boost</span><span class="special">::</span><span class="identifier">spirit</span><span class="special">::</span><span class="identifier">_e</span></code> </li> <li class="listitem"> <code class="computeroutput"><span class="identifier">boost</span><span class="special">::</span><span class="identifier">spirit</span><span class="special">::</span><span class="identifier">_f</span></code> </li> <li class="listitem"> <code class="computeroutput"><span class="identifier">boost</span><span class="special">::</span><span class="identifier">spirit</span><span class="special">::</span><span class="identifier">_g</span></code> </li> <li class="listitem"> <code class="computeroutput"><span class="identifier">boost</span><span class="special">::</span><span class="identifier">spirit</span><span class="special">::</span><span class="identifier">_h</span></code> </li> <li class="listitem"> <code class="computeroutput"><span class="identifier">boost</span><span class="special">::</span><span class="identifier">spirit</span><span class="special">::</span><span class="identifier">_i</span></code> </li> <li class="listitem"> <code class="computeroutput"><span class="identifier">boost</span><span class="special">::</span><span class="identifier">spirit</span><span class="special">::</span><span class="identifier">_j</span></code> </li> </ul></div> <p> which correspond to the Nonterminal's local variables <code class="computeroutput"><span class="identifier">T0</span></code> ... <code class="computeroutput"><span class="identifier">T9</span></code>. </p> <div class="variablelist"> <p class="title"><b>Notation</b></p> <dl> <dt><span class="term"><code class="computeroutput"><span class="identifier">x</span></code></span></dt> <dd><p> A Nonterminal </p></dd> <dt><span class="term"><code class="computeroutput"><span class="identifier">X</span></code></span></dt> <dd><p> A Nonterminal type </p></dd> <dt><span class="term"><code class="computeroutput"><span class="identifier">arg1</span></code>, <code class="computeroutput"><span class="identifier">arg2</span></code>, ..., <code class="computeroutput"><span class="identifier">argN</span></code></span></dt> <dd><p> <a class="link" href="../karma_basics.html#spirit.karma.reference.karma_basics.lazy_argument">Lazy Arguments</a> that evaluate to each of the Nonterminal's inherited attributes. </p></dd> </dl> </div> <a name="spirit.karma.reference.generator_concepts.nonterminal.valid_expressions"></a><h6> <a name="id1034498"></a> <a class="link" href="nonterminal.html#spirit.karma.reference.generator_concepts.nonterminal.valid_expressions">Valid Expressions</a> </h6> <p> In addition to the requirements defined in <a class="link" href="generator.html" title="Generator"><code class="computeroutput"><span class="identifier">Generator</span></code></a>, for any Nonterminal the following must be met: </p> <div class="informaltable"><table class="table"> <colgroup> <col> <col> <col> </colgroup> <thead><tr> <th> <p> Expression </p> </th> <th> <p> Semantics </p> </th> <th> <p> Return type </p> </th> </tr></thead> <tbody> <tr> <td> <p> <code class="computeroutput"><span class="identifier">x</span></code> </p> </td> <td> <p> In a generator expression, invoke Nonterminal <code class="computeroutput"><span class="identifier">x</span></code> </p> </td> <td> <p> <code class="computeroutput"><span class="identifier">X</span></code> </p> </td> </tr> <tr> <td> <p> <code class="computeroutput"><span class="identifier">x</span><span class="special">(</span><span class="identifier">arg1</span><span class="special">,</span> <span class="identifier">arg2</span><span class="special">,</span> <span class="special">...,</span> <span class="identifier">argN</span><span class="special">)</span></code> </p> </td> <td> <p> In a generator expression, invoke Nonterminal <code class="computeroutput"><span class="identifier">x</span></code> passing in inherited attributes <code class="computeroutput"><span class="identifier">arg1</span></code>...<code class="computeroutput"><span class="identifier">argN</span></code> </p> </td> <td> <p> <code class="computeroutput"><span class="identifier">X</span></code> </p> </td> </tr> <tr> <td> <p> <code class="computeroutput"><span class="identifier">x</span><span class="special">.</span><span class="identifier">name</span><span class="special">(</span><span class="identifier">name</span><span class="special">)</span></code> </p> </td> <td> <p> Set the name of a Nonterminal </p> </td> <td> <p> <code class="computeroutput"><span class="keyword">void</span></code> </p> </td> </tr> <tr> <td> <p> <code class="computeroutput"><span class="identifier">x</span><span class="special">.</span><span class="identifier">name</span><span class="special">()</span></code> </p> </td> <td> <p> Get the name of a Nonterminal </p> </td> <td> <p> <code class="computeroutput"><span class="identifier">std</span><span class="special">::</span><span class="identifier">string</span></code> </p> </td> </tr> </tbody> </table></div> <a name="spirit.karma.reference.generator_concepts.nonterminal.type_expressions"></a><h6> <a name="id1034824"></a> <a class="link" href="nonterminal.html#spirit.karma.reference.generator_concepts.nonterminal.type_expressions">Type Expressions</a> </h6> <div class="informaltable"><table class="table"> <colgroup> <col> <col> </colgroup> <thead><tr> <th> <p> Expression </p> </th> <th> <p> Description </p> </th> </tr></thead> <tbody> <tr> <td> <p> <code class="computeroutput"><span class="identifier">X</span><span class="special">::</span><span class="identifier">sig_type</span></code> </p> </td> <td> <p> The Signature of <code class="computeroutput"><span class="identifier">X</span></code>: An <a href="../../../../../../../../libs/mpl/doc/refmanual/forward-sequence.html" target="_top">MPL Forward Sequence</a>. The first element is the Nonterminal's consumed attribute type and the rest are the inherited attribute types. </p> </td> </tr> <tr> <td> <p> <code class="computeroutput"><span class="identifier">X</span><span class="special">::</span><span class="identifier">locals_type</span></code> </p> </td> <td> <p> The local variables of <code class="computeroutput"><span class="identifier">X</span></code>: An <a href="../../../../../../../../libs/mpl/doc/refmanual/forward-sequence.html" target="_top">MPL Forward Sequence</a>. </p> </td> </tr> </tbody> </table></div> <a name="spirit.karma.reference.generator_concepts.nonterminal.models"></a><h6> <a name="id1034965"></a> <a class="link" href="nonterminal.html#spirit.karma.reference.generator_concepts.nonterminal.models">Models</a> </h6> <div class="itemizedlist"><ul class="itemizedlist" type="disc"> <li class="listitem"> <a class="link" href="../nonterminal/rule.html" title="Rule">rule</a> </li> <li class="listitem"> <a class="link" href="../nonterminal/grammar.html" title="Grammar">grammar</a> </li> </ul></div> </div> <table xmlns:rev="http://www.cs.rpi.edu/~gregod/boost/tools/doc/revision" width="100%"><tr> <td align="left"></td> <td align="right"><div class="copyright-footer">Copyright © 2001-2010 Joel de Guzman, Hartmut Kaiser<p> Distributed under the Boost Software License, Version 1.0. (See accompanying file LICENSE_1_0.txt or copy at <a href="http://www.boost.org/LICENSE_1_0.txt" target="_top">http://www.boost.org/LICENSE_1_0.txt</a>) </p> </div></td> </tr></table> <hr> <div class="spirit-nav"> <a accesskey="p" href="narygenerator.html"><img src="../../../../../../../../doc/src/images/prev.png" alt="Prev"></a><a accesskey="u" href="../generator_concepts.html"><img src="../../../../../../../../doc/src/images/up.png" alt="Up"></a><a accesskey="h" href="../../../../index.html"><img src="../../../../../../../../doc/src/images/home.png" alt="Home"></a><a accesskey="n" href="../karma_basics.html"><img src="../../../../../../../../doc/src/images/next.png" alt="Next"></a> </div> </body> </html>