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| <div class="titlepage"><div><div><h5 class="title"> |
| <a name="spirit.qi.reference.parser_concepts.nonterminal"></a><a class="link" href="nonterminal.html" title="Nonterminal">Nonterminal</a> |
| </h5></div></div></div> |
| <a name="spirit.qi.reference.parser_concepts.nonterminal.description"></a><h6> |
| <a name="id844208"></a> |
| <a class="link" href="nonterminal.html#spirit.qi.reference.parser_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 parsing. |
| </p> |
| <a name="spirit.qi.reference.parser_concepts.nonterminal.refinement_of"></a><h6> |
| <a name="id844234"></a> |
| <a class="link" href="nonterminal.html#spirit.qi.reference.parser_concepts.nonterminal.refinement_of">Refinement |
| of</a> |
| </h6> |
| <div class="blockquote"><blockquote class="blockquote"><p> |
| <a class="link" href="parser.html" title="Parser"><code class="computeroutput"><span class="identifier">Parser</span></code></a> |
| </p></blockquote></div> |
| <a name="spirit.qi.reference.parser_concepts.nonterminal.signature"></a><h6> |
| <a name="id844269"></a> |
| <a class="link" href="nonterminal.html#spirit.qi.reference.parser_concepts.nonterminal.signature">Signature</a> |
| </h6> |
| <p> |
| Nonterminals can have both synthesized and inherited attributes. The |
| Nonterminal's <span class="emphasis"><em>Signature</em></span> specifies both the synthesized |
| 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 Nonterminal's |
| synthesized attribute and <code class="computeroutput"><span class="identifier">A0</span></code> |
| ... <code class="computeroutput"><span class="identifier">AN</span></code> are the Nonterminal's |
| inherited attributes. |
| </p> |
| <a name="spirit.qi.reference.parser_concepts.nonterminal.attributes"></a><h6> |
| <a name="id844370"></a> |
| <a class="link" href="nonterminal.html#spirit.qi.reference.parser_concepts.nonterminal.attributes">Attributes</a> |
| </h6> |
| <p> |
| The Nonterminal models a C++ function. The Nonterminal's synthesized |
| attribute is analogous to the function return value and its inherited |
| attributes are analogous to function arguments. The inherited attributes |
| (arguments) can be passed in just like any <a class="link" href="../basics.html#spirit.qi.reference.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.qi.reference.parser_concepts.nonterminal._code__phrase_role__identifier___val__phrase___code_"></a><h6> |
| <a name="id844417"></a> |
| <a class="link" href="nonterminal.html#spirit.qi.reference.parser_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">qi</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 (synthesized) attribute. The |
| <code class="computeroutput"><span class="identifier">_val</span></code> placeholder acts |
| like a mutable reference to the Nonterminal's attribute. |
| </p> |
| <a name="spirit.qi.reference.parser_concepts.nonterminal._code__phrase_role__identifier___r1__phrase___code_______code__phrase_role__identifier__r10__phrase___code_"></a><h6> |
| <a name="id844484"></a> |
| <a class="link" href="nonterminal.html#spirit.qi.reference.parser_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.qi.reference.parser_concepts.nonterminal.locals"></a><h6> |
| <a name="id844565"></a> |
| <a class="link" href="nonterminal.html#spirit.qi.reference.parser_concepts.nonterminal.locals">Locals</a> |
| </h6> |
| <p> |
| Nonterminals can have local variables that will be created on the stack |
| at parse time. 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="../basics.html#spirit.qi.reference.basics.lazy_argument">Lazy Arguments</a> |
| that evaluate to each of the Nonterminal's inherited attributes. |
| </p></dd> |
| </dl> |
| </div> |
| <a name="spirit.qi.reference.parser_concepts.nonterminal.valid_expressions"></a><h6> |
| <a name="id845081"></a> |
| <a class="link" href="nonterminal.html#spirit.qi.reference.parser_concepts.nonterminal.valid_expressions">Valid |
| Expressions</a> |
| </h6> |
| <p> |
| In addition to the requirements defined in <a class="link" href="parser.html" title="Parser"><code class="computeroutput"><span class="identifier">Parser</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 parser 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 parser expression, invoke Nonterminal <code class="computeroutput"><span class="identifier">r</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> |
| Naming 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> |
| Getting 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> |
| <tr> |
| <td> |
| <p> |
| debug(x) |
| </p> |
| </td> |
| <td> |
| <p> |
| Debug Nonterminal <code class="computeroutput"><span class="identifier">x</span></code>. |
| </p> |
| </td> |
| <td> |
| <p> |
| <code class="computeroutput"><span class="keyword">void</span></code> |
| </p> |
| </td> |
| </tr> |
| </tbody> |
| </table></div> |
| <a name="spirit.qi.reference.parser_concepts.nonterminal.type_expressions"></a><h6> |
| <a name="id845446"></a> |
| <a class="link" href="nonterminal.html#spirit.qi.reference.parser_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 |
| synthesized 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.qi.reference.parser_concepts.nonterminal.models"></a><h6> |
| <a name="id845591"></a> |
| <a class="link" href="nonterminal.html#spirit.qi.reference.parser_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> |
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