<html> <head> <meta http-equiv="Content-Type" content="text/html; charset=US-ASCII"> <title>And-Predicate (&a)</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="../operator.html" title="Operator"> <link rel="prev" href="alternative.html" title="Alternative (a | b)"> <link rel="next" href="difference.html" title="Difference (a - b)"> </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="alternative.html"><img src="../../../../../../../../doc/src/images/prev.png" alt="Prev"></a><a accesskey="u" href="../operator.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="difference.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.qi.reference.operator.and_predicate"></a><a class="link" href="and_predicate.html" title="And-Predicate (&a)"> And-Predicate (<code class="computeroutput"><span class="special">&</span><span class="identifier">a</span></code>)</a> </h5></div></div></div> <a name="spirit.qi.reference.operator.and_predicate.description"></a><h6> <a name="id965696"></a> <a class="link" href="and_predicate.html#spirit.qi.reference.operator.and_predicate.description">Description</a> </h6> <p> Syntactic predicates assert a certain conditional syntax to be satisfied before evaluating another production. Similar to semantic predicates, <a class="link" href="../auxiliary/eps.html" title="Epsilon (eps)"><code class="computeroutput"><span class="identifier">eps</span></code></a>, syntactic predicates do not consume any input. The <span class="emphasis"><em>and-predicate</em></span>, <code class="computeroutput"><span class="special">&</span><span class="identifier">a</span></code>, is a positive syntactic predicate that returns a zero length match only if its predicate matches. </p> <a name="spirit.qi.reference.operator.and_predicate.header"></a><h6> <a name="id965737"></a> <a class="link" href="and_predicate.html#spirit.qi.reference.operator.and_predicate.header">Header</a> </h6> <pre class="programlisting"><span class="comment">// forwards to <boost/spirit/home/qi/operator/and_predicate.hpp> </span><span class="preprocessor">#include</span> <span class="special"><</span><span class="identifier">boost</span><span class="special">/</span><span class="identifier">spirit</span><span class="special">/</span><span class="identifier">include</span><span class="special">/</span><span class="identifier">qi_and_predicate</span><span class="special">.</span><span class="identifier">hpp</span><span class="special">></span> </pre> <p> Also, see <a class="link" href="../../../structure/include.html" title="Include">Include Structure</a>. </p> <a name="spirit.qi.reference.operator.and_predicate.model_of"></a><h6> <a name="id965811"></a> <a class="link" href="and_predicate.html#spirit.qi.reference.operator.and_predicate.model_of">Model of</a> </h6> <div class="blockquote"><blockquote class="blockquote"><p> <a class="link" href="../parser_concepts/unaryparser.html" title="UnaryParser"><code class="computeroutput"><span class="identifier">UnaryParser</span></code></a> </p></blockquote></div> <div class="variablelist"> <p class="title"><b>Notation</b></p> <dl> <dt><span class="term"><code class="computeroutput"><span class="identifier">a</span></code></span></dt> <dd><p> A <a class="link" href="../parser_concepts/parser.html" title="Parser"><code class="computeroutput"><span class="identifier">Parser</span></code></a> </p></dd> </dl> </div> <a name="spirit.qi.reference.operator.and_predicate.expression_semantics"></a><h6> <a name="id965879"></a> <a class="link" href="and_predicate.html#spirit.qi.reference.operator.and_predicate.expression_semantics">Expression Semantics</a> </h6> <p> Semantics of an expression is defined only where it differs from, or is not defined in <a class="link" href="../parser_concepts/unaryparser.html" title="UnaryParser"><code class="computeroutput"><span class="identifier">UnaryParser</span></code></a>. </p> <div class="informaltable"><table class="table"> <colgroup> <col> <col> </colgroup> <thead><tr> <th> <p> Expression </p> </th> <th> <p> Semantics </p> </th> </tr></thead> <tbody><tr> <td> <p> <code class="computeroutput"><span class="special">&</span><span class="identifier">a</span></code> </p> </td> <td> <p> If the predicate <code class="computeroutput"><span class="identifier">a</span></code> matches, return a zero length match. Otherwise, fail. </p> </td> </tr></tbody> </table></div> <a name="spirit.qi.reference.operator.and_predicate.attributes"></a><h6> <a name="id965979"></a> <a class="link" href="and_predicate.html#spirit.qi.reference.operator.and_predicate.attributes">Attributes</a> </h6> <p> See <a class="link" href="../../quick_reference/compound_attribute_rules.html#spirit.qi.quick_reference.compound_attribute_rules.notation">Compound Attribute Notation</a>. </p> <div class="informaltable"><table class="table"> <colgroup> <col> <col> </colgroup> <thead><tr> <th> <p> Expression </p> </th> <th> <p> Attribute </p> </th> </tr></thead> <tbody><tr> <td> <p> <code class="computeroutput"><span class="special">&</span><span class="identifier">a</span></code> </p> </td> <td> <p> <code class="computeroutput"><span class="identifier">unused_type</span></code> </p> </td> </tr></tbody> </table></div> <a name="spirit.qi.reference.operator.and_predicate.complexity"></a><h6> <a name="id966074"></a> <a class="link" href="and_predicate.html#spirit.qi.reference.operator.and_predicate.complexity">Complexity</a> </h6> <div class="blockquote"><blockquote class="blockquote"><p> The complexity is defined by the complexity of the predicate, <code class="computeroutput"><span class="identifier">a</span></code> </p></blockquote></div> <a name="spirit.qi.reference.operator.and_predicate.example"></a><h6> <a name="id966101"></a> <a class="link" href="and_predicate.html#spirit.qi.reference.operator.and_predicate.example">Example</a> </h6> <div class="note"><table border="0" summary="Note"> <tr> <td rowspan="2" align="center" valign="top" width="25"><img alt="[Note]" src="../../../../images/note.png"></td> <th align="left">Note</th> </tr> <tr><td align="left" valign="top"><p> The test harness for the example(s) below is presented in the <a class="link" href="../basics.html#spirit.qi.reference.basics.examples">Basics Examples</a> section. </p></td></tr> </table></div> <p> Some using declarations: </p> <p> </p> <pre class="programlisting"><span class="keyword">using</span> <span class="identifier">boost</span><span class="special">::</span><span class="identifier">spirit</span><span class="special">::</span><span class="identifier">lit</span><span class="special">;</span></pre> <p> </p> <p> Basic look-ahead example: make sure that the last character is a semicolon, but don't consume it, just peek at the next character: </p> <p> </p> <pre class="programlisting"><span class="identifier">test_phrase_parser</span><span class="special">(</span><span class="string">"Hello ;"</span><span class="special">,</span> <span class="identifier">lit</span><span class="special">(</span><span class="string">"Hello"</span><span class="special">)</span> <span class="special">>></span> <span class="special">&</span><span class="identifier">lit</span><span class="special">(</span><span class="char">';'</span><span class="special">),</span> <span class="keyword">false</span><span class="special">);</span> </pre> <p> </p> </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="alternative.html"><img src="../../../../../../../../doc/src/images/prev.png" alt="Prev"></a><a accesskey="u" href="../operator.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="difference.html"><img src="../../../../../../../../doc/src/images/next.png" alt="Next"></a> </div> </body> </html>