| <html> |
| <head> |
| <meta http-equiv="Content-Type" content="text/html; charset=US-ASCII"> |
| <title>Action</title> |
| <link rel="stylesheet" href="../../../../../../../doc/src/boostbook.css" type="text/css"> |
| <meta name="generator" content="DocBook XSL Stylesheets V1.75.0"> |
| <link rel="home" href="../../../index.html" title="Spirit 2.4.1"> |
| <link rel="up" href="../reference.html" title="Reference"> |
| <link rel="prev" href="generate_api/create_generator.html" title="API for Automatic Generator Creation"> |
| <link rel="next" href="auto.html" title="Auto"> |
| </head> |
| <body bgcolor="white" text="black" link="#0000FF" vlink="#840084" alink="#0000FF"> |
| <table cellpadding="2" width="100%"><tr> |
| <td valign="top"><img alt="Boost C++ Libraries" width="277" height="86" src="../../../../../../../boost.png"></td> |
| <td align="center"><a href="../../../../../../../index.html">Home</a></td> |
| <td align="center"><a href="../../../../../../../libs/libraries.htm">Libraries</a></td> |
| <td align="center"><a href="http://www.boost.org/users/people.html">People</a></td> |
| <td align="center"><a href="http://www.boost.org/users/faq.html">FAQ</a></td> |
| <td align="center"><a href="../../../../../../../more/index.htm">More</a></td> |
| </tr></table> |
| <hr> |
| <div class="spirit-nav"> |
| <a accesskey="p" href="generate_api/create_generator.html"><img src="../../../../../../../doc/src/images/prev.png" alt="Prev"></a><a accesskey="u" href="../reference.html"><img src="../../../../../../../doc/src/images/up.png" alt="Up"></a><a accesskey="h" href="../../../index.html"><img src="../../../../../../../doc/src/images/home.png" alt="Home"></a><a accesskey="n" href="auto.html"><img src="../../../../../../../doc/src/images/next.png" alt="Next"></a> |
| </div> |
| <div class="section"> |
| <div class="titlepage"><div><div><h4 class="title"> |
| <a name="spirit.karma.reference.action"></a><a class="link" href="action.html" title="Action">Action</a> |
| </h4></div></div></div> |
| <a name="spirit.karma.reference.action.description"></a><h6> |
| <a name="id1004244"></a> |
| <a class="link" href="action.html#spirit.karma.reference.action.description">Description</a> |
| </h6> |
| <p> |
| Semantic actions may be attached to any point in the grammar specification. |
| They allow to call a function or function object in order to provide the |
| value output by the generator attached to the semantic action. Semantic |
| actions are associated with a generator using the syntax <code class="computeroutput"><span class="identifier">g</span><span class="special">[]</span></code>, |
| where <code class="computeroutput"><span class="identifier">g</span></code> is an arbitrary |
| generator expression. |
| </p> |
| <a name="spirit.karma.reference.action.header"></a><h6> |
| <a name="id1004280"></a> |
| <a class="link" href="action.html#spirit.karma.reference.action.header">Header</a> |
| </h6> |
| <pre class="programlisting"><span class="comment">// forwards to <boost/spirit/home/karma/action.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_action</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.action.model_of"></a><h6> |
| <a name="id1004354"></a> |
| <a class="link" href="action.html#spirit.karma.reference.action.model_of">Model of</a> |
| </h6> |
| <div class="blockquote"><blockquote class="blockquote"><p> |
| <a class="link" href="generator_concepts/unarygenerator.html" title="UnaryGenerator"><code class="computeroutput"><span class="identifier">UnaryGenerator</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>, <code class="computeroutput"><span class="identifier">g</span></code></span></dt> |
| <dd><p> |
| Instances of a generator, <code class="computeroutput"><span class="identifier">G</span></code> |
| </p></dd> |
| <dt><span class="term"><code class="computeroutput"><span class="identifier">A</span></code></span></dt> |
| <dd><p> |
| Attribute type exposed by a generator, <code class="computeroutput"><span class="identifier">a</span></code> |
| </p></dd> |
| <dt><span class="term"><code class="computeroutput"><span class="identifier">fa</span></code></span></dt> |
| <dd><p> |
| A (semantic action) function with signature <code class="computeroutput"><span class="keyword">void</span><span class="special">(</span><span class="identifier">Attrib</span><span class="special">&,</span> <span class="identifier">Context</span><span class="special">&,</span> <span class="keyword">bool</span><span class="special">&)</span></code>. The third parameter is a boolean |
| flag that can be set to false to force the generator to fail. Both |
| <code class="computeroutput"><span class="identifier">Context</span></code> and the boolean |
| flag are optional. For more information see below. |
| </p></dd> |
| <dt><span class="term"><code class="computeroutput"><span class="identifier">Attrib</span></code></span></dt> |
| <dd><p> |
| The attribute to be used to generate output from. |
| </p></dd> |
| <dt><span class="term"><code class="computeroutput"><span class="identifier">Context</span></code></span></dt> |
| <dd><p> |
| The type of the generator execution context. For more information |
| see below. |
| </p></dd> |
| </dl> |
| </div> |
| <a name="spirit.karma.reference.action.expression_semantics"></a><h6> |
| <a name="id1004556"></a> |
| <a class="link" href="action.html#spirit.karma.reference.action.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/unarygenerator.html" title="UnaryGenerator"><code class="computeroutput"><span class="identifier">UnaryGenerator</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">g</span><span class="special">[</span><span class="identifier">fa</span><span class="special">]</span></code> |
| </p> |
| </td> |
| <td> |
| <p> |
| Call semantic action, <code class="computeroutput"><span class="identifier">fa</span></code> |
| <span class="emphasis"><em>before</em></span> invoking <code class="computeroutput"><span class="identifier">g</span></code>. |
| The function or function object <code class="computeroutput"><span class="identifier">fa</span></code> |
| is expected to provide the value to generate output from to the |
| generator <code class="computeroutput"><span class="identifier">g</span></code>. |
| </p> |
| </td> |
| </tr></tbody> |
| </table></div> |
| <p> |
| The possible signatures for functions to be used as semantic actions are: |
| </p> |
| <pre class="programlisting"><span class="keyword">template</span> <span class="special"><</span><span class="keyword">typename</span> <span class="identifier">Attrib</span><span class="special">></span> |
| <span class="keyword">void</span> <span class="identifier">fa</span><span class="special">(</span><span class="identifier">Attrib</span><span class="special">&</span> <span class="identifier">attr</span><span class="special">);</span> |
| |
| <span class="keyword">template</span> <span class="special"><</span><span class="keyword">typename</span> <span class="identifier">Attrib</span><span class="special">,</span> <span class="keyword">typename</span> <span class="identifier">Context</span><span class="special">></span> |
| <span class="keyword">void</span> <span class="identifier">fa</span><span class="special">(</span><span class="identifier">Attrib</span><span class="special">&</span> <span class="identifier">attr</span><span class="special">,</span> <span class="identifier">Context</span><span class="special">&</span> <span class="identifier">context</span><span class="special">);</span> |
| |
| <span class="keyword">template</span> <span class="special"><</span><span class="keyword">typename</span> <span class="identifier">Attrib</span><span class="special">,</span> <span class="keyword">typename</span> <span class="identifier">Context</span><span class="special">></span> |
| <span class="keyword">void</span> <span class="identifier">fa</span><span class="special">(</span><span class="identifier">Attrib</span><span class="special">&</span> <span class="identifier">attr</span><span class="special">,</span> <span class="identifier">Context</span><span class="special">&</span> <span class="identifier">context</span><span class="special">,</span> <span class="keyword">bool</span><span class="special">&</span> <span class="identifier">pass</span><span class="special">);</span> |
| </pre> |
| <p> |
| The function or function object is expected to return the value to generate |
| output from by assigning it to the first parameter, <code class="computeroutput"><span class="identifier">attr</span></code>. |
| Here <code class="computeroutput"><span class="identifier">Attrib</span></code> is the attribute |
| type of the generator attached to the semantic action. |
| </p> |
| <p> |
| The type <code class="computeroutput"><span class="identifier">Context</span></code> is the |
| type of the generator execution context. This type is unspecified and depends |
| on the context the generator is invoked in. The value <code class="computeroutput"><span class="identifier">context</span></code> |
| is used by semantic actions written using <a href="../../../../../phoenix/doc/html/index.html" target="_top">Phoenix</a> |
| to access various context dependent attributes and values. For more information |
| about <a href="../../../../../phoenix/doc/html/index.html" target="_top">Phoenix</a> placeholder |
| expressions usable in semantic actions see <a class="link" href="generator_concepts/nonterminal.html" title="Nonterminal"><code class="computeroutput"><span class="identifier">Nonterminal</span></code></a>. |
| </p> |
| <p> |
| The third parameter, <code class="computeroutput"><span class="identifier">pass</span></code>, |
| can be used by the semantic action to force the associated generator to |
| fail. If pass is set to <code class="computeroutput"><span class="keyword">false</span></code> |
| the action generator will immediately return <code class="computeroutput"><span class="keyword">false</span></code> |
| as well, while not invoking <code class="computeroutput"><span class="identifier">g</span></code> |
| and not generating any output. |
| </p> |
| <a name="spirit.karma.reference.action.attributes"></a><h6> |
| <a name="id1005012"></a> |
| <a class="link" href="action.html#spirit.karma.reference.action.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">a</span><span class="special">[</span><span class="identifier">fa</span><span class="special">]</span></code> |
| </p> |
| </td> |
| <td> |
| <p> |
| <code class="computeroutput"><span class="identifier">a</span><span class="special">:</span> |
| <span class="identifier">A</span> <span class="special">--></span> |
| <span class="identifier">a</span><span class="special">[</span><span class="identifier">fa</span><span class="special">]:</span> |
| <span class="identifier">A</span></code> |
| </p> |
| </td> |
| </tr></tbody> |
| </table></div> |
| <a name="spirit.karma.reference.action.complexity"></a><h6> |
| <a name="id1005137"></a> |
| <a class="link" href="action.html#spirit.karma.reference.action.complexity">Complexity</a> |
| </h6> |
| <p> |
| The complexity of the action generator is defined by the complexity of |
| the generator the semantic action is attached to and the complexity of |
| the function or function object used as the semantic action. |
| </p> |
| <div class="important"><table border="0" summary="Important"> |
| <tr> |
| <td rowspan="2" align="center" valign="top" width="25"><img alt="[Important]" src="../../../images/important.png"></td> |
| <th align="left">Important</th> |
| </tr> |
| <tr><td align="left" valign="top"><p> |
| Please note that the use of semantic actions in <span class="emphasis"><em>Spirit.Karma</em></span> |
| generally forces the library to create a <span class="emphasis"><em>copy</em></span> of |
| the attribute, which might be a costly operation. Always consider using |
| other means of associating a value with a particular generator first. |
| </p></td></tr> |
| </table></div> |
| <a name="spirit.karma.reference.action.example"></a><h6> |
| <a name="id1005169"></a> |
| <a class="link" href="action.html#spirit.karma.reference.action.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">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">int_</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">string</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">phoenix</span><span class="special">::</span><span class="identifier">ref</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> |
| Some examples: |
| </p> |
| <p> |
| |
| </p> |
| <pre class="programlisting"><span class="keyword">int</span> <span class="identifier">i</span> <span class="special">=</span> <span class="number">42</span><span class="special">;</span> |
| <span class="identifier">test_generator</span><span class="special">(</span><span class="string">"42"</span><span class="special">,</span> <span class="identifier">int_</span><span class="special">[</span><span class="identifier">_1</span> <span class="special">=</span> <span class="identifier">ref</span><span class="special">(</span><span class="identifier">i</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">string</span><span class="special">[</span><span class="identifier">_1</span> <span class="special">=</span> <span class="identifier">val</span><span class="special">(</span><span class="string">"abc"</span><span class="special">)]);</span> |
| </pre> |
| <p> |
| </p> |
| <p> |
| More examples for semantic actions can be found here: <a class="link" href="../tutorials/semantic_actions.html#spirit.karma.tutorials.semantic_actions.examples_of_semantic_actions">Examples |
| of Semantic Actions</a>. |
| </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> |
| </tr></table> |
| <hr> |
| <div class="spirit-nav"> |
| <a accesskey="p" href="generate_api/create_generator.html"><img src="../../../../../../../doc/src/images/prev.png" alt="Prev"></a><a accesskey="u" href="../reference.html"><img src="../../../../../../../doc/src/images/up.png" alt="Up"></a><a accesskey="h" href="../../../index.html"><img src="../../../../../../../doc/src/images/home.png" alt="Home"></a><a accesskey="n" href="auto.html"><img src="../../../../../../../doc/src/images/next.png" alt="Next"></a> |
| </div> |
| </body> |
| </html> |
