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| <div class="section"> |
| <div class="titlepage"><div><div><h5 class="title"> |
| <a name="spirit.karma.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.karma.reference.auxiliary.lazy.description"></a><h6> |
| <a name="id1013831"></a> |
| <a class="link" href="lazy.html#spirit.karma.reference.auxiliary.lazy.description">Description</a> |
| </h6> |
| <p> |
| The family of <code class="computeroutput"><span class="identifier">lazy</span></code> components |
| allows to use a dynamically returned generator component for output generation. |
| It calls the provided function or function object at generate time using |
| its return value as the actual generator to produce the output. |
| </p> |
| <a name="spirit.karma.reference.auxiliary.lazy.header"></a><h6> |
| <a name="id1013855"></a> |
| <a class="link" href="lazy.html#spirit.karma.reference.auxiliary.lazy.header">Header</a> |
| </h6> |
| <pre class="programlisting"><span class="comment">// forwards to <boost/spirit/home/karma/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">karma_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.karma.reference.auxiliary.lazy.namespace"></a><h6> |
| <a name="id1013930"></a> |
| <a class="link" href="lazy.html#spirit.karma.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::karma::lazy</span></code> |
| </p> |
| </td></tr></tbody> |
| </table></div> |
| <a name="spirit.karma.reference.auxiliary.lazy.model_of"></a><h6> |
| <a name="id1015921"></a> |
| <a class="link" href="lazy.html#spirit.karma.reference.auxiliary.lazy.model_of">Model |
| of</a> |
| </h6> |
| <div class="blockquote"><blockquote class="blockquote"><p> |
| <a class="link" href="../generator_concepts/generator.html" title="Generator"><code class="computeroutput"><span class="identifier">Generator</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">fg</span></code></span></dt> |
| <dd><p> |
| A function or function object that evaluates to a generator object |
| (an object exposing the <a class="link" href="../generator_concepts/generator.html" title="Generator"><code class="computeroutput"><span class="identifier">Generator</span></code></a>). This function |
| will be invoked at generate time. |
| </p></dd> |
| </dl> |
| </div> |
| <p> |
| The signature of <code class="computeroutput"><span class="identifier">fg</span></code> is |
| expected to be |
| </p> |
| <pre class="programlisting"><span class="identifier">G</span> <span class="identifier">f</span><span class="special">(</span><span class="identifier">Unused</span><span class="special">,</span> <span class="identifier">Context</span><span class="special">)</span> |
| </pre> |
| <p> |
| where <code class="computeroutput"><span class="identifier">G</span></code>, the function's |
| return value, is the type of the generator to be invoked, and <code class="computeroutput"><span class="identifier">Context</span></code> is the generator's Context |
| type (The first argument is <code class="computeroutput"><span class="identifier">unused</span></code> |
| to make the <code class="computeroutput"><span class="identifier">Context</span></code> the |
| second argument. This is done for uniformity with <a class="link" href="../../tutorials/semantic_actions.html" title="Semantic Actions">Semantic |
| Actions</a>). |
| </p> |
| <a name="spirit.karma.reference.auxiliary.lazy.expression_semantics"></a><h6> |
| <a name="id1016070"></a> |
| <a class="link" href="lazy.html#spirit.karma.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="../generator_concepts/generator.html" title="Generator"><code class="computeroutput"><span class="identifier">Generator</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">fg</span></code> |
| </p> |
| </td> |
| <td> |
| <p> |
| The <a href="../../../../../../phoenix/doc/html/index.html" target="_top">Boost.Phoenix</a> |
| function object <code class="computeroutput"><span class="identifier">fg</span></code> |
| will be invoked at generate time. It is expected to return |
| a generator instance. This generator is then invoked in order |
| to generate the output. This generator will succeed as long |
| as the invoked generated succeeds as well (unless the underlying |
| output stream reports an error). |
| </p> |
| </td> |
| </tr> |
| <tr> |
| <td> |
| <p> |
| <code class="computeroutput"><span class="identifier">lazy</span><span class="special">(</span><span class="identifier">fg</span><span class="special">)</span></code> |
| </p> |
| </td> |
| <td> |
| <p> |
| The function or function object will be invoked at generate |
| time. It is expected to return a generator instance (note this |
| version of <code class="computeroutput"><span class="identifier">lazy</span></code> |
| does not require <code class="computeroutput"><span class="identifier">fg</span></code> |
| to be a <a href="../../../../../../phoenix/doc/html/index.html" target="_top">Boost.Phoenix</a> |
| function object). This generator is then invoked in order to |
| generate the output. This generator will succeed as long as |
| the invoked generated succeeds as well (except if the underlying |
| output stream reports an error). |
| </p> |
| </td> |
| </tr> |
| </tbody> |
| </table></div> |
| <a name="spirit.karma.reference.auxiliary.lazy.attributes"></a><h6> |
| <a name="id1016226"></a> |
| <a class="link" href="lazy.html#spirit.karma.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">fg</span></code> |
| </p> |
| </td> |
| <td> |
| <p> |
| The attribute type <code class="computeroutput"><span class="identifier">G</span></code> |
| as exposed by the generator <code class="computeroutput"><span class="identifier">g</span></code> |
| returned from <code class="computeroutput"><span class="identifier">fg</span></code>. |
| </p> |
| </td> |
| </tr> |
| <tr> |
| <td> |
| <p> |
| <code class="computeroutput"><span class="identifier">lazy</span><span class="special">(</span><span class="identifier">fg</span><span class="special">)</span></code> |
| </p> |
| </td> |
| <td> |
| <p> |
| The attribute type <code class="computeroutput"><span class="identifier">G</span></code> |
| as exposed by the generator <code class="computeroutput"><span class="identifier">g</span></code> |
| returned from <code class="computeroutput"><span class="identifier">fg</span></code>. |
| </p> |
| </td> |
| </tr> |
| </tbody> |
| </table></div> |
| <a name="spirit.karma.reference.auxiliary.lazy.complexity"></a><h6> |
| <a name="id1016378"></a> |
| <a class="link" href="lazy.html#spirit.karma.reference.auxiliary.lazy.complexity">Complexity</a> |
| </h6> |
| <p> |
| The complexity of the <code class="computeroutput"><span class="identifier">lazy</span></code> |
| component is determined by the complexity of the generator returned from |
| <code class="computeroutput"><span class="identifier">fg</span></code>. |
| </p> |
| <a name="spirit.karma.reference.auxiliary.lazy.example"></a><h6> |
| <a name="id1016409"></a> |
| <a class="link" href="lazy.html#spirit.karma.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="../karma_basics.html#spirit.karma.reference.karma_basics.examples">Basics Examples</a> |
| section. |
| </p></td></tr> |
| </table></div> |
| <p> |
| Some includes: |
| </p> |
| <p> |
| |
| </p> |
| <pre class="programlisting"><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">karma</span><span class="special">.</span><span class="identifier">hpp</span><span class="special">></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">phoenix_core</span><span class="special">.</span><span class="identifier">hpp</span><span class="special">></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">phoenix_operator</span><span class="special">.</span><span class="identifier">hpp</span><span class="special">></span> |
| <span class="preprocessor">#include</span> <span class="special"><</span><span class="identifier">boost</span><span class="special">/</span><span class="identifier">fusion</span><span class="special">/</span><span class="identifier">include</span><span class="special">/</span><span class="identifier">std_pair</span><span class="special">.</span><span class="identifier">hpp</span><span class="special">></span> |
| <span class="preprocessor">#include</span> <span class="special"><</span><span class="identifier">iostream</span><span class="special">></span> |
| <span class="preprocessor">#include</span> <span class="special"><</span><span class="identifier">string</span><span class="special">></span> |
| </pre> |
| <p> |
| </p> |
| <p> |
| Some using declarations: |
| </p> |
| <p> |
| |
| </p> |
| <pre class="programlisting"><span class="keyword">namespace</span> <span class="identifier">karma</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">karma</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">karma</span><span class="special">::</span><span class="identifier">_1</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> |
| Basic usage of the <code class="computeroutput"><span class="identifier">lazy</span></code> |
| generator: |
| </p> |
| <p> |
| |
| </p> |
| <pre class="programlisting"><span class="identifier">test_generator_attr</span><span class="special">(</span><span class="string">"abc"</span><span class="special">,</span> <span class="identifier">karma</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">"abc"</span><span class="special">);</span> |
| <span class="identifier">test_generator</span><span class="special">(</span><span class="string">"abc"</span><span class="special">,</span> <span class="identifier">karma</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="identifier">_1</span> <span class="special">=</span> <span class="string">"abc"</span><span class="special">]);</span> |
| </pre> |
| <p> |
| </p> |
| </div> |
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| <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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