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| <title>Not-Predicate (!a)</title> |
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| <div class="titlepage"><div><div><h5 class="title"> |
| <a name="spirit.qi.reference.operator.not_predicate"></a><a class="link" href="not_predicate.html" title="Not-Predicate (!a)">Not-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.not_predicate.description"></a><h6> |
| <a name="id933668"></a> |
| <a class="link" href="not_predicate.html#spirit.qi.reference.operator.not_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>not-predicate</em></span>, |
| <code class="computeroutput"><span class="special">!</span><span class="identifier">a</span></code>, |
| is a negative syntactic predicate that returns a zero length match only |
| if its predicate fails to match. |
| </p> |
| <a name="spirit.qi.reference.operator.not_predicate.header"></a><h6> |
| <a name="id933709"></a> |
| <a class="link" href="not_predicate.html#spirit.qi.reference.operator.not_predicate.header">Header</a> |
| </h6> |
| <pre class="programlisting"><span class="comment">// forwards to <boost/spirit/home/qi/operator/not_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_not_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.not_predicate.model_of"></a><h6> |
| <a name="id933783"></a> |
| <a class="link" href="not_predicate.html#spirit.qi.reference.operator.not_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.not_predicate.expression_semantics"></a><h6> |
| <a name="id933851"></a> |
| <a class="link" href="not_predicate.html#spirit.qi.reference.operator.not_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, fail. Otherwise, return a zero length match. |
| </p> |
| </td> |
| </tr></tbody> |
| </table></div> |
| <a name="spirit.qi.reference.operator.not_predicate.attributes"></a><h6> |
| <a name="id933951"></a> |
| <a class="link" href="not_predicate.html#spirit.qi.reference.operator.not_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.not_predicate.complexity"></a><h6> |
| <a name="id934046"></a> |
| <a class="link" href="not_predicate.html#spirit.qi.reference.operator.not_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.not_predicate.example"></a><h6> |
| <a name="id934073"></a> |
| <a class="link" href="not_predicate.html#spirit.qi.reference.operator.not_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">ascii</span><span class="special">::</span><span class="identifier">char_</span><span class="special">;</span> |
| <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">ascii</span><span class="special">::</span><span class="identifier">alpha</span><span class="special">;</span> |
| <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">lit</span><span class="special">;</span> |
| <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">symbols</span><span class="special">;</span></pre> |
| <p> |
| </p> |
| <p> |
| Here's an alternative to the <code class="computeroutput"><span class="special">*(</span><span class="identifier">r</span> <span class="special">-</span> <span class="identifier">x</span><span class="special">)</span> <span class="special">>></span> <span class="identifier">x</span></code> |
| idiom using the not-predicate instead. This parses a list of characters |
| terminated by a ';': |
| </p> |
| <p> |
| |
| </p> |
| <pre class="programlisting"><span class="identifier">test_parser</span><span class="special">(</span><span class="string">"abcdef;"</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="special">>></span> <span class="identifier">char_</span><span class="special">)</span> <span class="special">>></span> <span class="char">';'</span><span class="special">);</span></pre> |
| <p> |
| </p> |
| <p> |
| The following parser ensures that we match distinct keywords (stored |
| in a symbol table). To do this, we make sure that the keyword does not |
| follow an alpha or an underscore: |
| </p> |
| <p> |
| |
| </p> |
| <pre class="programlisting"><span class="identifier">symbols</span><span class="special"><</span><span class="keyword">char</span><span class="special">,</span> <span class="keyword">int</span><span class="special">></span> <span class="identifier">keywords</span><span class="special">;</span> |
| <span class="identifier">keywords</span> <span class="special">=</span> <span class="string">"begin"</span><span class="special">,</span> <span class="string">"end"</span><span class="special">,</span> <span class="string">"for"</span><span class="special">;</span> |
| |
| <span class="comment">// This should fail: |
| </span><span class="identifier">test_parser</span><span class="special">(</span><span class="string">"beginner"</span><span class="special">,</span> <span class="identifier">keywords</span> <span class="special">>></span> <span class="special">!(</span><span class="identifier">alpha</span> <span class="special">|</span> <span class="char">'_'</span><span class="special">));</span> |
| |
| <span class="comment">// This is ok: |
| </span><span class="identifier">test_parser</span><span class="special">(</span><span class="string">"end "</span><span class="special">,</span> <span class="identifier">keywords</span> <span class="special">>></span> <span class="special">!(</span><span class="identifier">alpha</span> <span class="special">|</span> <span class="char">'_'</span><span class="special">),</span> <span class="keyword">false</span><span class="special">);</span> |
| |
| <span class="comment">// This is ok: |
| </span><span class="identifier">test_parser</span><span class="special">(</span><span class="string">"for()"</span><span class="special">,</span> <span class="identifier">keywords</span> <span class="special">>></span> <span class="special">!(</span><span class="identifier">alpha</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> |
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| <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>) |
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