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

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  26 <div class="titlepage"><div><div><h5 class="title">
  27 <a name="spirit.qi.reference.operator.sequential_or"></a><a class="link" href="sequential_or.html" title="Sequential Or Parser (a || b)">Sequential
  28           Or Parser (<code class="computeroutput"><span class="identifier">a</span> <span class="special">||</span>
  29           <span class="identifier">b</span></code>)</a>
  30 </h5></div></div></div>
  31 <h6>
  32 <a name="spirit.qi.reference.operator.sequential_or.h0"></a>
  33             <span><a name="spirit.qi.reference.operator.sequential_or.description"></a></span><a class="link" href="sequential_or.html#spirit.qi.reference.operator.sequential_or.description">Description</a>
  34           </h6>
  35 <p>
  36             The sequential-or operator, <code class="computeroutput"><span class="identifier">a</span>
  37             <span class="special">||</span> <span class="identifier">b</span></code>,
  38             matches <code class="computeroutput"><span class="identifier">a</span></code> or <code class="computeroutput"><span class="identifier">b</span></code> or <code class="computeroutput"><span class="identifier">a</span></code>
  39             followed by <code class="computeroutput"><span class="identifier">b</span></code>. That is,
  40             if both <code class="computeroutput"><span class="identifier">a</span></code> and <code class="computeroutput"><span class="identifier">b</span></code> match, it must be in sequence; this
  41             is equivalent to <code class="computeroutput"><span class="identifier">a</span> <span class="special">&gt;&gt;</span>
  42             <span class="special">-</span><span class="identifier">b</span>
  43             <span class="special">|</span> <span class="identifier">b</span></code>:
  44           </p>
  45 <pre class="programlisting"><span class="identifier">a</span> <span class="special">||</span> <span class="identifier">b</span> <span class="special">||</span> <span class="special">...</span>
  46 </pre>
  47 <h6>
  48 <a name="spirit.qi.reference.operator.sequential_or.h1"></a>
  49             <span><a name="spirit.qi.reference.operator.sequential_or.header"></a></span><a class="link" href="sequential_or.html#spirit.qi.reference.operator.sequential_or.header">Header</a>
  50           </h6>
  51 <pre class="programlisting"><span class="comment">// forwards to &lt;boost/spirit/home/qi/operator/sequential_or.hpp&gt;</span>
  52 <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_sequential_or</span><span class="special">.</span><span class="identifier">hpp</span><span class="special">&gt;</span>
  53 </pre>
  54 <p>
  55             Also, see <a class="link" href="../../../structure/include.html" title="Include">Include Structure</a>.
  56           </p>
  57 <h6>
  58 <a name="spirit.qi.reference.operator.sequential_or.h2"></a>
  59             <span><a name="spirit.qi.reference.operator.sequential_or.model_of"></a></span><a class="link" href="sequential_or.html#spirit.qi.reference.operator.sequential_or.model_of">Model of</a>
  60           </h6>
  61 <div class="blockquote"><blockquote class="blockquote"><p>
  62               <a class="link" href="../parser_concepts/naryparser.html" title="NaryParser"><code class="computeroutput"><span class="identifier">NaryParser</span></code></a>
  63             </p></blockquote></div>
  64 <div class="variablelist">
  65 <p class="title"><b>Notation</b></p>
  66 <dl>
  67 <dt><span class="term"><code class="computeroutput"><span class="identifier">a</span></code>, <code class="computeroutput"><span class="identifier">b</span></code></span></dt>
  68 <dd><p>
  69                   A <a class="link" href="../parser_concepts/parser.html" title="Parser"><code class="computeroutput"><span class="identifier">Parser</span></code></a>
  70                 </p></dd>
  71 </dl>
  72 </div>
  73 <h6>
  74 <a name="spirit.qi.reference.operator.sequential_or.h3"></a>
  75             <span><a name="spirit.qi.reference.operator.sequential_or.expression_semantics"></a></span><a class="link" href="sequential_or.html#spirit.qi.reference.operator.sequential_or.expression_semantics">Expression
  76             Semantics</a>
  77           </h6>
  78 <p>
  79             Semantics of an expression is defined only where it differs from, or
  80             is not defined in <a class="link" href="../parser_concepts/naryparser.html" title="NaryParser"><code class="computeroutput"><span class="identifier">NaryParser</span></code></a>.
  81           </p>
  82 <div class="informaltable"><table class="table">
  83 <colgroup>
  84 <col>
  85 <col>
  86 </colgroup>
  87 <thead><tr>
  88 <th>
  89                     <p>
  90                       Expression
  91                     </p>
  92                   </th>
  93 <th>
  94                     <p>
  95                       Semantics
  96                     </p>
  97                   </th>
  98 </tr></thead>
  99 <tbody><tr>
 100 <td>
 101                     <p>
 102                       <code class="computeroutput"><span class="identifier">a</span> <span class="special">||</span>
 103                       <span class="identifier">b</span></code>
 104                     </p>
 105                   </td>
 106 <td>
 107                     <p>
 108                       Match <code class="computeroutput"><span class="identifier">a</span></code> or
 109                       <code class="computeroutput"><span class="identifier">b</span></code> in sequence.
 110                       equivalent to <code class="computeroutput"><span class="identifier">a</span> <span class="special">&gt;&gt;</span> <span class="special">-</span><span class="identifier">b</span> <span class="special">|</span>
 111                       <span class="identifier">b</span></code>
 112                     </p>
 113                   </td>
 114 </tr></tbody>
 115 </table></div>
 116 <h6>
 117 <a name="spirit.qi.reference.operator.sequential_or.h4"></a>
 118             <span><a name="spirit.qi.reference.operator.sequential_or.attributes"></a></span><a class="link" href="sequential_or.html#spirit.qi.reference.operator.sequential_or.attributes">Attributes</a>
 119           </h6>
 120 <p>
 121             See <a class="link" href="../../quick_reference/compound_attribute_rules.html#spirit.qi.quick_reference.compound_attribute_rules.notation">Compound
 122             Attribute Notation</a>.
 123           </p>
 124 <div class="informaltable"><table class="table">
 125 <colgroup>
 126 <col>
 127 <col>
 128 </colgroup>
 129 <thead><tr>
 130 <th>
 131                     <p>
 132                       Expression
 133                     </p>
 134                   </th>
 135 <th>
 136                     <p>
 137                       Attribute
 138                     </p>
 139                   </th>
 140 </tr></thead>
 141 <tbody><tr>
 142 <td>
 143                     <p>
 144                       <code class="computeroutput"><span class="identifier">a</span> <span class="special">||</span>
 145                       <span class="identifier">b</span></code>
 146                     </p>
 147                   </td>
 148 <td>
 149                     <p>
 150 </p>
 151 <pre xmlns:rev="http://www.cs.rpi.edu/~gregod/boost/tools/doc/revision" class="table-programlisting"><span class="identifier">a</span><span class="special">:</span> <span class="identifier">A</span><span class="special">,</span> <span class="identifier">b</span><span class="special">:</span> <span class="identifier">B</span> <span class="special">--&gt;</span> <span class="special">(</span><span class="identifier">a</span> <span class="special">||</span> <span class="identifier">b</span><span class="special">):</span> <span class="identifier">tuple</span><span class="special">&lt;</span><span class="identifier">optional</span><span class="special">&lt;</span><span class="identifier">A</span><span class="special">&gt;,</span> <span class="identifier">optional</span><span class="special">&lt;</span><span class="identifier">B</span><span class="special">&gt;</span> <span class="special">&gt;</span>
 152 <span class="identifier">a</span><span class="special">:</span> <span class="identifier">A</span><span class="special">,</span> <span class="identifier">b</span><span class="special">:</span> <span class="identifier">Unused</span> <span class="special">--&gt;</span> <span class="special">(</span><span class="identifier">a</span> <span class="special">||</span> <span class="identifier">b</span><span class="special">):</span> <span class="identifier">optional</span><span class="special">&lt;</span><span class="identifier">A</span><span class="special">&gt;</span>
 153 <span class="identifier">a</span><span class="special">:</span> <span class="identifier">Unused</span><span class="special">,</span> <span class="identifier">b</span><span class="special">:</span> <span class="identifier">B</span> <span class="special">--&gt;</span> <span class="special">(</span><span class="identifier">a</span> <span class="special">||</span> <span class="identifier">b</span><span class="special">):</span> <span class="identifier">optional</span><span class="special">&lt;</span><span class="identifier">B</span><span class="special">&gt;</span>
 154 <span class="identifier">a</span><span class="special">:</span> <span class="identifier">Unused</span><span class="special">,</span> <span class="identifier">b</span><span class="special">:</span> <span class="identifier">Unused</span> <span class="special">--&gt;</span> <span class="special">(</span><span class="identifier">a</span> <span class="special">||</span> <span class="identifier">b</span><span class="special">):</span> <span class="identifier">Unused</span>
 155
 156 <span class="identifier">a</span><span class="special">:</span> <span class="identifier">A</span><span class="special">,</span> <span class="identifier">b</span><span class="special">:</span> <span class="identifier">A</span> <span class="special">--&gt;</span> <span class="special">(</span><span class="identifier">a</span> <span class="special">||</span> <span class="identifier">b</span><span class="special">):</span> <span class="identifier">vector</span><span class="special">&lt;</span><span class="identifier">optional</span><span class="special">&lt;</span><span class="identifier">A</span><span class="special">&gt;</span> <span class="special">&gt;</span></pre>
 157 <p>
 158                     </p>
 159                   </td>
 160 </tr></tbody>
 161 </table></div>
 162 <div class="note"><table border="0" summary="Note">
 163 <tr>
 164 <td rowspan="2" align="center" valign="top" width="25"><img alt="[Note]" src="../../../../images/note.png"></td>
 165 <th align="left">Note</th>
 166 </tr>
 167 <tr><td align="left" valign="top">
 168 <p>
 169               The sequential-or parser behaves attribute-wise very similar to the
 170               plain sequence parser (<code class="computeroutput"><span class="identifier">a</span>
 171               <span class="special">&gt;&gt;</span> <span class="identifier">b</span></code>)
 172               in the sense that it exposes the attributes of its elements separately.
 173               For instance, if you attach a semantic action to the whole sequential-or:
 174 </p>
 175 <pre class="programlisting"><span class="special">(</span><span class="identifier">int_</span> <span class="special">||</span> <span class="identifier">int_</span><span class="special">)[</span><span class="identifier">print_pair</span><span class="special">(</span><span class="identifier">_1</span><span class="special">,</span> <span class="identifier">_2</span><span class="special">)]</span>
 176 </pre>
 177 <p>
 178               the function object <code class="computeroutput"><span class="identifier">print_pair</span></code>
 179               would be invoked with the attribute of the first <code class="computeroutput"><span class="identifier">int_</span></code>
 180               (<code class="computeroutput"><span class="identifier">boost</span><span class="special">::</span><span class="identifier">optional</span><span class="special">&lt;</span><span class="keyword">int</span><span class="special">&gt;</span></code>)
 181               as its first parameter and the attribute of the second <code class="computeroutput"><span class="identifier">int_</span></code> (<code class="computeroutput"><span class="identifier">boost</span><span class="special">::</span><span class="identifier">optional</span><span class="special">&lt;</span><span class="keyword">int</span><span class="special">&gt;</span></code> as well) as its second parameter.
 182             </p>
 183 </td></tr>
 184 </table></div>
 185 <h6>
 186 <a name="spirit.qi.reference.operator.sequential_or.h5"></a>
 187             <span><a name="spirit.qi.reference.operator.sequential_or.complexity"></a></span><a class="link" href="sequential_or.html#spirit.qi.reference.operator.sequential_or.complexity">Complexity</a>
 188           </h6>
 189 <div class="blockquote"><blockquote class="blockquote"><p>
 190               The overall complexity of the sequential-or parser is defined by the
 191               sum of the complexities of its elements. The complexity of the sequential-or
 192               itself is O(N), where N is the number of elements in the sequence.
 193             </p></blockquote></div>
 194 <h6>
 195 <a name="spirit.qi.reference.operator.sequential_or.h6"></a>
 196             <span><a name="spirit.qi.reference.operator.sequential_or.example"></a></span><a class="link" href="sequential_or.html#spirit.qi.reference.operator.sequential_or.example">Example</a>
 197           </h6>
 198 <div class="note"><table border="0" summary="Note">
 199 <tr>
 200 <td rowspan="2" align="center" valign="top" width="25"><img alt="[Note]" src="../../../../images/note.png"></td>
 201 <th align="left">Note</th>
 202 </tr>
 203 <tr><td align="left" valign="top"><p>
 204               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>
 205               section.
 206             </p></td></tr>
 207 </table></div>
 208 <p>
 209             Some using declarations:
 210           </p>
 211 <p>
 212 </p>
 213 <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">qi</span><span class="special">::</span><span class="identifier">int_</span><span class="special">;</span>
 214 </pre>
 215 <p>
 216           </p>
 217 <p>
 218             Correctly parsing a number with optional fractional digits:
 219           </p>
 220 <p>
 221 </p>
 222 <pre class="programlisting"><span class="identifier">test_parser</span><span class="special">(</span><span class="string">"123.456"</span><span class="special">,</span> <span class="identifier">int_</span> <span class="special">||</span> <span class="special">(</span><span class="char">'.'</span> <span class="special">&gt;&gt;</span> <span class="identifier">int_</span><span class="special">));</span>  <span class="comment">// full</span>
 223 <span class="identifier">test_parser</span><span class="special">(</span><span class="string">"123"</span><span class="special">,</span> <span class="identifier">int_</span> <span class="special">||</span> <span class="special">(</span><span class="char">'.'</span> <span class="special">&gt;&gt;</span> <span class="identifier">int_</span><span class="special">));</span>      <span class="comment">// just the whole number</span>
 224 <span class="identifier">test_parser</span><span class="special">(</span><span class="string">".456"</span><span class="special">,</span> <span class="identifier">int_</span> <span class="special">||</span> <span class="special">(</span><span class="char">'.'</span> <span class="special">&gt;&gt;</span> <span class="identifier">int_</span><span class="special">));</span>     <span class="comment">// just the fraction</span>
 225 </pre>
 226 <p>
 227           </p>
 228 <p>
 229             A naive but incorrect solution would try to do this using optionals (e.g.):
 230           </p>
 231 <pre class="programlisting"><span class="identifier">int_</span> <span class="special">&gt;&gt;</span> <span class="special">-(</span><span class="char">'.'</span> <span class="special">&gt;&gt;</span> <span class="identifier">int_</span><span class="special">)</span>  <span class="comment">// will not match ".456"</span>
 232 <span class="special">-</span><span class="identifier">int_</span> <span class="special">&gt;&gt;</span> <span class="special">(</span><span class="char">'.'</span> <span class="special">&gt;&gt;</span> <span class="identifier">int_</span><span class="special">)</span>  <span class="comment">// will not match "123"</span>
 233 <span class="special">-</span><span class="identifier">int_</span> <span class="special">&gt;&gt;</span> <span class="special">-(</span><span class="char">'.'</span> <span class="special">&gt;&gt;</span> <span class="identifier">int_</span><span class="special">)</span> <span class="comment">// will match empty strings! Ooops.</span>
 234 </pre>
 235 </div>
 236 <table xmlns:rev="http://www.cs.rpi.edu/~gregod/boost/tools/doc/revision" width="100%"><tr>
 237 <td align="left"></td>
 238 <td align="right"><div class="copyright-footer">Copyright &#169; 2001-2011 Joel de Guzman, Hartmut Kaiser<p>
 239         Distributed under the Boost Software License, Version 1.0. (See accompanying
 240         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>)
 241       </p>
 242 </div></td>
 243 </tr></table>
 244 <hr>
 245 <div class="spirit-nav">
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