libs/spirit/doc/html/spirit/qi/reference/operator/and_predicate.html

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   4 <title>And-Predicate Parser (&amp;a)</title>
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  26 <div class="titlepage"><div><div><h5 class="title">
  27 <a name="spirit.qi.reference.operator.and_predicate"></a><a class="link" href="and_predicate.html" title="And-Predicate Parser (&amp;a)">And-Predicate
  28           Parser (<code class="computeroutput"><span class="special">&amp;</span><span class="identifier">a</span></code>)</a>
  29 </h5></div></div></div>
  30 <h6>
  31 <a name="spirit.qi.reference.operator.and_predicate.h0"></a>
  32             <span class="phrase"><a name="spirit.qi.reference.operator.and_predicate.description"></a></span><a class="link" href="and_predicate.html#spirit.qi.reference.operator.and_predicate.description">Description</a>
  33           </h6>
  34 <p>
  35             Syntactic predicates assert a certain conditional syntax to be satisfied
  36             before evaluating another production. Similar to semantic predicates,
  37             <a class="link" href="../auxiliary/eps.html" title="Epsilon Parser (eps)"><code class="computeroutput"><span class="identifier">eps</span></code></a>,
  38             syntactic predicates do not consume any input. The <span class="emphasis"><em>and-predicate</em></span>,
  39             <code class="computeroutput"><span class="special">&amp;</span><span class="identifier">a</span></code>,
  40             is a positive syntactic predicate that returns a zero length match only
  41             if its predicate matches.
  42           </p>
  43 <h6>
  44 <a name="spirit.qi.reference.operator.and_predicate.h1"></a>
  45             <span class="phrase"><a name="spirit.qi.reference.operator.and_predicate.header"></a></span><a class="link" href="and_predicate.html#spirit.qi.reference.operator.and_predicate.header">Header</a>
  46           </h6>
  47 <pre class="programlisting"><span class="comment">// forwards to &lt;boost/spirit/home/qi/operator/and_predicate.hpp&gt;</span>
  48 <span class="preprocessor">#include</span> <span class="special">&lt;</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">&gt;</span>
  49 </pre>
  50 <p>
  51             Also, see <a class="link" href="../../../structure/include.html" title="Include">Include Structure</a>.
  52           </p>
  53 <h6>
  54 <a name="spirit.qi.reference.operator.and_predicate.h2"></a>
  55             <span class="phrase"><a name="spirit.qi.reference.operator.and_predicate.model_of"></a></span><a class="link" href="and_predicate.html#spirit.qi.reference.operator.and_predicate.model_of">Model of</a>
  56           </h6>
  57 <div class="blockquote"><blockquote class="blockquote"><p>
  58               <a class="link" href="../parser_concepts/unaryparser.html" title="UnaryParser"><code class="computeroutput"><span class="identifier">UnaryParser</span></code></a>
  59             </p></blockquote></div>
  60 <div class="variablelist">
  61 <p class="title"><b>Notation</b></p>
  62 <dl class="variablelist">
  63 <dt><span class="term"><code class="computeroutput"><span class="identifier">a</span></code></span></dt>
  64 <dd><p>
  65                   A <a class="link" href="../parser_concepts/parser.html" title="Parser"><code class="computeroutput"><span class="identifier">Parser</span></code></a>
  66                 </p></dd>
  67 </dl>
  68 </div>
  69 <h6>
  70 <a name="spirit.qi.reference.operator.and_predicate.h3"></a>
  71             <span class="phrase"><a name="spirit.qi.reference.operator.and_predicate.expression_semantics"></a></span><a class="link" href="and_predicate.html#spirit.qi.reference.operator.and_predicate.expression_semantics">Expression
  72             Semantics</a>
  73           </h6>
  74 <p>
  75             Semantics of an expression is defined only where it differs from, or
  76             is not defined in <a class="link" href="../parser_concepts/unaryparser.html" title="UnaryParser"><code class="computeroutput"><span class="identifier">UnaryParser</span></code></a>.
  77           </p>
  78 <div class="informaltable"><table class="table">
  79 <colgroup>
  80 <col>
  81 <col>
  82 </colgroup>
  83 <thead><tr>
  84 <th>
  85                     <p>
  86                       Expression
  87                     </p>
  88                   </th>
  89 <th>
  90                     <p>
  91                       Semantics
  92                     </p>
  93                   </th>
  94 </tr></thead>
  95 <tbody><tr>
  96 <td>
  97                     <p>
  98                       <code class="computeroutput"><span class="special">&amp;</span><span class="identifier">a</span></code>
  99                     </p>
 100                   </td>
 101 <td>
 102                     <p>
 103                       If the predicate <code class="computeroutput"><span class="identifier">a</span></code>
 104                       matches, return a zero length match. Otherwise, fail.
 105                     </p>
 106                   </td>
 107 </tr></tbody>
 108 </table></div>
 109 <h6>
 110 <a name="spirit.qi.reference.operator.and_predicate.h4"></a>
 111             <span class="phrase"><a name="spirit.qi.reference.operator.and_predicate.attributes"></a></span><a class="link" href="and_predicate.html#spirit.qi.reference.operator.and_predicate.attributes">Attributes</a>
 112           </h6>
 113 <p>
 114             See <a class="link" href="../../quick_reference/compound_attribute_rules.html#spirit.qi.quick_reference.compound_attribute_rules.notation">Compound
 115             Attribute Notation</a>.
 116           </p>
 117 <div class="informaltable"><table class="table">
 118 <colgroup>
 119 <col>
 120 <col>
 121 </colgroup>
 122 <thead><tr>
 123 <th>
 124                     <p>
 125                       Expression
 126                     </p>
 127                   </th>
 128 <th>
 129                     <p>
 130                       Attribute
 131                     </p>
 132                   </th>
 133 </tr></thead>
 134 <tbody><tr>
 135 <td>
 136                     <p>
 137                       <code class="computeroutput"><span class="special">&amp;</span><span class="identifier">a</span></code>
 138                     </p>
 139                   </td>
 140 <td>
 141                     <p>
 142                       <code class="computeroutput"><span class="identifier">unused_type</span></code>
 143                     </p>
 144                   </td>
 145 </tr></tbody>
 146 </table></div>
 147 <h6>
 148 <a name="spirit.qi.reference.operator.and_predicate.h5"></a>
 149             <span class="phrase"><a name="spirit.qi.reference.operator.and_predicate.complexity"></a></span><a class="link" href="and_predicate.html#spirit.qi.reference.operator.and_predicate.complexity">Complexity</a>
 150           </h6>
 151 <div class="blockquote"><blockquote class="blockquote"><p>
 152               The complexity is defined by the complexity of the predicate, <code class="computeroutput"><span class="identifier">a</span></code>
 153             </p></blockquote></div>
 154 <h6>
 155 <a name="spirit.qi.reference.operator.and_predicate.h6"></a>
 156             <span class="phrase"><a name="spirit.qi.reference.operator.and_predicate.example"></a></span><a class="link" href="and_predicate.html#spirit.qi.reference.operator.and_predicate.example">Example</a>
 157           </h6>
 158 <div class="note"><table border="0" summary="Note">
 159 <tr>
 160 <td rowspan="2" align="center" valign="top" width="25"><img alt="[Note]" src="../../../../images/note.png"></td>
 161 <th align="left">Note</th>
 162 </tr>
 163 <tr><td align="left" valign="top"><p>
 164               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>
 165               section.
 166             </p></td></tr>
 167 </table></div>
 168 <p>
 169             Some using declarations:
 170           </p>
 171 <p>
 172 </p>
 173 <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>
 174 </pre>
 175 <p>
 176           </p>
 177 <p>
 178             Basic look-ahead example: make sure that the last character is a semicolon,
 179             but don't consume it, just peek at the next character:
 180           </p>
 181 <p>
 182 </p>
 183 <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">&gt;&gt;</span> <span class="special">&amp;</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>
 184 </pre>
 185 <p>
 186           </p>
 187 </div>
 188 <table xmlns:rev="http://www.cs.rpi.edu/~gregod/boost/tools/doc/revision" width="100%"><tr>
 189 <td align="left"></td>
 190 <td align="right"><div class="copyright-footer">Copyright &#169; 2001-2011 Joel de Guzman, Hartmut Kaiser<p>
 191         Distributed under the Boost Software License, Version 1.0. (See accompanying
 192         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>)
 193       </p>
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