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| <div class="titlepage"><div><div><h5 class="title"> |
| <a name="spirit.qi.reference.auxiliary.lazy"></a><a class="link" href="lazy.html" title="Lazy (lazy)">Lazy (<code class="computeroutput"><span class="identifier">lazy</span></code>)</a> |
| </h5></div></div></div> |
| <a name="spirit.qi.reference.auxiliary.lazy.description"></a><h6> |
| <a name="id868457"></a> |
| <a class="link" href="lazy.html#spirit.qi.reference.auxiliary.lazy.description">Description</a> |
| </h6> |
| <p> |
| The <code class="computeroutput"><span class="identifier">lazy</span></code> parser, as its |
| name suggests, invokes a lazy <a href="../../../../../../phoenix/doc/html/index.html" target="_top">Phoenix</a> |
| function that returns a parser at parse time. This parser will be used |
| once it is created to continue the parse. |
| </p> |
| <a name="spirit.qi.reference.auxiliary.lazy.header"></a><h6> |
| <a name="id868487"></a> |
| <a class="link" href="lazy.html#spirit.qi.reference.auxiliary.lazy.header">Header</a> |
| </h6> |
| <pre class="programlisting"><span class="comment">// forwards to <boost/spirit/home/qi/auxiliary/lazy.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_lazy</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.auxiliary.lazy.namespace"></a><h6> |
| <a name="id868561"></a> |
| <a class="link" href="lazy.html#spirit.qi.reference.auxiliary.lazy.namespace">Namespace</a> |
| </h6> |
| <div class="informaltable"><table class="table"> |
| <colgroup><col></colgroup> |
| <thead><tr><th> |
| <p> |
| Name |
| </p> |
| </th></tr></thead> |
| <tbody><tr><td> |
| <p> |
| <code class="computeroutput"><span class="identifier">boost</span><span class="special">::</span><span class="identifier">spirit</span><span class="special">::</span><span class="identifier">lazy</span> <span class="comment">// alias: |
| boost::spirit::qi::lazy</span></code> |
| </p> |
| </td></tr></tbody> |
| </table></div> |
| <a name="spirit.qi.reference.auxiliary.lazy.model_of"></a><h6> |
| <a name="id868639"></a> |
| <a class="link" href="lazy.html#spirit.qi.reference.auxiliary.lazy.model_of">Model of</a> |
| </h6> |
| <div class="blockquote"><blockquote class="blockquote"><p> |
| <a class="link" href="../parser_concepts/parser.html" title="Parser"><code class="computeroutput"><span class="identifier">Parser</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">fp</span></code></span></dt> |
| <dd><p> |
| A <a class="link" href="../basics.html#spirit.qi.reference.basics.lazy_argument">Lazy |
| Argument</a> that evaluates to 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.auxiliary.lazy.expression_semantics"></a><h6> |
| <a name="id868710"></a> |
| <a class="link" href="lazy.html#spirit.qi.reference.auxiliary.lazy.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/parser.html" title="Parser"><code class="computeroutput"><span class="identifier">Parser</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="identifier">fp</span></code> |
| </p> |
| </td> |
| <td> |
| <p> |
| Create a lazy-parser from a <a class="link" href="../basics.html#spirit.qi.reference.basics.lazy_argument">Lazy |
| Argument</a>, <code class="computeroutput"><span class="identifier">fp</span></code>. |
| <code class="computeroutput"><span class="identifier">fp</span></code> will be |
| invoked at parse time. <code class="computeroutput"><span class="identifier">fp</span></code> |
| is expected to return a <a class="link" href="../parser_concepts/parser.html" title="Parser"><code class="computeroutput"><span class="identifier">Parser</span></code></a> object. This |
| parser is then invoked in order to parse the input. |
| </p> |
| </td> |
| </tr> |
| <tr> |
| <td> |
| <p> |
| <code class="computeroutput"><span class="identifier">lazy</span><span class="special">(</span><span class="identifier">fp</span><span class="special">)</span></code> |
| </p> |
| </td> |
| <td> |
| <p> |
| Create a lazy-parser from a <a class="link" href="../basics.html#spirit.qi.reference.basics.lazy_argument">Lazy |
| Argument</a>, <code class="computeroutput"><span class="identifier">fp</span></code>. |
| <code class="computeroutput"><span class="identifier">fp</span></code> will be |
| invoked at parse time. <code class="computeroutput"><span class="identifier">fp</span></code> |
| is expected to return a <a class="link" href="../parser_concepts/parser.html" title="Parser"><code class="computeroutput"><span class="identifier">Parser</span></code></a> object. This |
| parser is then invoked in order to parse the input. |
| </p> |
| </td> |
| </tr> |
| </tbody> |
| </table></div> |
| <a name="spirit.qi.reference.auxiliary.lazy.attributes"></a><h6> |
| <a name="id868904"></a> |
| <a class="link" href="lazy.html#spirit.qi.reference.auxiliary.lazy.attributes">Attributes</a> |
| </h6> |
| <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="identifier">fp</span></code> |
| </p> |
| </td> |
| <td> |
| <p> |
| The attribute type of the return type of <code class="computeroutput"><span class="identifier">fp</span></code>. |
| </p> |
| </td> |
| </tr> |
| <tr> |
| <td> |
| <p> |
| <code class="computeroutput"><span class="identifier">lazy</span><span class="special">(</span><span class="identifier">fp</span><span class="special">)</span></code> |
| </p> |
| </td> |
| <td> |
| <p> |
| The attribute type of the return type of <code class="computeroutput"><span class="identifier">fp</span></code>. |
| </p> |
| </td> |
| </tr> |
| </tbody> |
| </table></div> |
| <a name="spirit.qi.reference.auxiliary.lazy.complexity"></a><h6> |
| <a name="id869028"></a> |
| <a class="link" href="lazy.html#spirit.qi.reference.auxiliary.lazy.complexity">Complexity</a> |
| </h6> |
| <p> |
| The complexity of the <code class="computeroutput"><span class="identifier">lazy</span></code> |
| parser is determined by the complexity of the parser returned from <code class="computeroutput"><span class="identifier">fp</span></code>. |
| </p> |
| <a name="spirit.qi.reference.auxiliary.lazy.example"></a><h6> |
| <a name="id869059"></a> |
| <a class="link" href="lazy.html#spirit.qi.reference.auxiliary.lazy.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">qi</span><span class="special">::</span><span class="identifier">lazy</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">string</span><span class="special">;</span> |
| <span class="keyword">using</span> <span class="identifier">boost</span><span class="special">::</span><span class="identifier">phoenix</span><span class="special">::</span><span class="identifier">val</span><span class="special">;</span> |
| </pre> |
| <p> |
| </p> |
| <p> |
| Using <code class="computeroutput"><span class="identifier">lazy</span></code>: |
| </p> |
| <p> |
| Here, the phoenix::val expression creates a function that returns its |
| argument when invoked. The lazy expression defers the invocation of this |
| function at parse time. Then, this parser (string parser) is called into |
| action. All this takes place at parse time. |
| </p> |
| <p> |
| |
| </p> |
| <pre class="programlisting"><span class="identifier">test_parser</span><span class="special">(</span><span class="string">"Hello"</span><span class="special">,</span> <span class="identifier">lazy</span><span class="special">(</span><span class="identifier">val</span><span class="special">(</span><span class="identifier">string</span><span class="special">(</span><span class="string">"Hello"</span><span class="special">))));</span></pre> |
| <p> |
| </p> |
| <p> |
| The above is equivalent to: |
| </p> |
| <p> |
| |
| </p> |
| <pre class="programlisting"><span class="identifier">test_parser</span><span class="special">(</span><span class="string">"Hello"</span><span class="special">,</span> <span class="identifier">val</span><span class="special">(</span><span class="identifier">string</span><span class="special">(</span><span class="string">"Hello"</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> |
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