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| <div class="refentry"> |
| <a name="Expr"></a><div class="titlepage"></div> |
| <div class="refnamediv"> |
| <h2><span class="refentrytitle">Concept Expr</span></h2> |
| <p>Expr</p> |
| </div> |
| <div class="refsect1"> |
| <a name="id2456652"></a><h2>Description</h2> |
| <p> |
| An Expr represents a tagged node in an expression tree. |
| The children of the Expr must themselves satisfy the |
| Expr concept. The Expr has an arity representing the |
| number of children. If the number of children is zero, |
| the Expr also has a value. An Expr also has an associated |
| <a class="link" href="Domain.html" title="Concept Domain">Domain</a>. |
| </p> |
| </div> |
| <div class="refsect1"> |
| <a name="id2456672"></a><h2>Associated types</h2> |
| <div class="itemizedlist"><ul class="itemizedlist" type="disc"> |
| <li class="listitem"> |
| <p><span class="bold"><strong>proto_tag</strong></span></p> |
| <pre class="literallayout">Expr::proto_tag</pre> |
| <p> |
| </p> |
| <p>The tag type of the Expr.</p> |
| <p> |
| </p> |
| </li> |
| <li class="listitem"> |
| <p><span class="bold"><strong>proto_args</strong></span></p> |
| <pre class="literallayout">Expr::proto_args</pre> |
| <p> |
| </p> |
| <p>A typelist representing either the types of the child nodes, or, |
| if the arity of the Expr is 0, of the value of the terminal.</p> |
| <p> |
| </p> |
| </li> |
| <li class="listitem"> |
| <p><span class="bold"><strong>proto_arity</strong></span></p> |
| <pre class="literallayout">Expr::proto_arity</pre> |
| <p> |
| </p> |
| <p> |
| The arity (number of child nodes) of the Expr. |
| <code class="computeroutput">proto_arity</code> is an MPL Integral Constant. |
| </p> |
| <p> |
| </p> |
| </li> |
| <li class="listitem"> |
| <p><span class="bold"><strong>proto_grammar</strong></span></p> |
| <pre class="literallayout">Expr::proto_grammar</pre> |
| <p> |
| </p> |
| <p> |
| A typedef for an instantiation of |
| <code class="computeroutput"><a class="link" href="boost/proto/basic_expr.html" title="Struct template basic_expr"> |
| proto::basic_expr<> |
| </a></code> |
| that is equivalent to Expr. Expression types are equivalent if they have the |
| same <code class="computeroutput">proto_tag</code>, <code class="computeroutput">proto_args</code>, and <code class="computeroutput">proto_arity</code>. |
| </p> |
| <p> |
| </p> |
| </li> |
| <li class="listitem"> |
| <p><span class="bold"><strong>proto_base_expr</strong></span></p> |
| <pre class="literallayout">Expr::proto_base_expr</pre> |
| <p> |
| </p> |
| <p> |
| A typedef for an instantiation of |
| <code class="computeroutput"><a class="link" href="boost/proto/expr.html" title="Struct template expr">proto::expr<></a></code> or |
| <code class="computeroutput"><a class="link" href="boost/proto/basic_expr.html" title="Struct template basic_expr">proto::basic_expr<></a></code> |
| that is equivalent to Expr. Expression types are equivalent if they have the |
| same <code class="computeroutput">proto_tag</code>, <code class="computeroutput">proto_args</code>, and <code class="computeroutput">proto_arity</code>. |
| </p> |
| <p> |
| </p> |
| </li> |
| <li class="listitem"> |
| <p><span class="bold"><strong>proto_derived_expr</strong></span></p> |
| <pre class="literallayout">Expr::proto_derived_expr</pre> |
| <p> |
| </p> |
| <p> |
| A typedef for <code class="computeroutput">Expr</code>. |
| </p> |
| <p> |
| </p> |
| </li> |
| <li class="listitem"> |
| <p><span class="bold"><strong>proto_domain</strong></span></p> |
| <pre class="literallayout">Expr::proto_domain</pre> |
| <p> |
| </p> |
| <p> |
| The Domain of the Expr. <code class="computeroutput">proto_domain</code> |
| models <a class="link" href="Domain.html" title="Concept Domain">Domain</a>. |
| </p> |
| <p> |
| </p> |
| </li> |
| <li class="listitem"> |
| <p><span class="bold"><strong>proto_childN</strong></span></p> |
| <pre class="literallayout">Expr::proto_childN</pre> |
| <p> |
| </p> |
| <p>The type of the Nth child of Expr. Requires |
| <code class="computeroutput">0 == N::value || N::value < proto_arity::value</code></p> |
| <p> |
| </p> |
| </li> |
| </ul></div> |
| </div> |
| <div class="refsect1"> |
| <a name="id2456931"></a><h2>Notation</h2> |
| <div class="variablelist"><dl> |
| <dt><span class="term">Expr</span></dt> |
| <dd>A type playing the role of expession-type in the <a class="link" href="Expr.html" title="Concept Expr">Expr</a> concept.</dd> |
| <dt><span class="term">Tag</span></dt> |
| <dd>A type playing the role of tag-type in the <a class="link" href="Expr.html" title="Concept Expr">Expr</a> concept.</dd> |
| <dt><span class="term">Domain</span></dt> |
| <dd>A type playing the role of domain-type in the <a class="link" href="Expr.html" title="Concept Expr">Expr</a> concept.</dd> |
| <dt><span class="term">N</span></dt> |
| <dd>A type playing the role of mpl-integral-constant-type in the <a class="link" href="Expr.html" title="Concept Expr">Expr</a> concept.</dd> |
| <dt><span class="term"><code class="varname">e</code></span></dt> |
| <dd>Object of type Expr</dd> |
| </dl></div> |
| </div> |
| <div class="refsect1"> |
| <a name="id2457000"></a><h2>Valid expressions</h2> |
| <div class="informaltable"><table class="table"> |
| <colgroup> |
| <col> |
| <col> |
| <col> |
| <col> |
| </colgroup> |
| <thead><tr> |
| <th>Name</th> |
| <th>Expression</th> |
| <th>Type</th> |
| <th>Semantics</th> |
| </tr></thead> |
| <tbody> |
| <tr> |
| <td><p>Get N-th Child</p></td> |
| <td><p>boost::proto::child< N >(e)</p></td> |
| <td><p><span class="type">proto_childN</span></p></td> |
| <td><p>Extracts the Nth child from this Expr. |
| Requires <code class="computeroutput">N::value < proto_arity::value</code>.</p></td> |
| </tr> |
| <tr> |
| <td><p>Get Terminal Value</p></td> |
| <td><p>boost::proto::value(e)</p></td> |
| <td><p><span class="type">proto_child0</span></p></td> |
| <td><p> |
| Extracts the value from a terminal Expr. |
| Requires <code class="computeroutput">0 == proto_arity::value</code>. |
| </p></td> |
| </tr> |
| <tr> |
| <td><p>Get Base</p></td> |
| <td><p>e.proto_base()</p></td> |
| <td><p><span class="type">proto_base_expr</span></p></td> |
| <td><p> |
| Returns an object of type |
| <code class="computeroutput"><a class="link" href="boost/proto/expr.html" title="Struct template expr">proto::expr<></a></code> or |
| <code class="computeroutput"><a class="link" href="boost/proto/basic_expr.html" title="Struct template basic_expr">proto::basic_expr<></a></code> |
| that is equivalent to <code class="computeroutput">e</code>. |
| </p></td> |
| </tr> |
| </tbody> |
| </table></div> |
| </div> |
| <div class="refsect1"> |
| <a name="id2457113"></a><h2>Models</h2> |
| <div class="itemizedlist"><ul class="itemizedlist" type="disc"><li class="listitem"><span class="simplelist"><span class="type">boost::proto::literal< int ></span></span></li></ul></div> |
| </div> |
| </div> |
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| <td align="left"></td> |
| <td align="right"><div class="copyright-footer">Copyright © 2008 Eric Niebler<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> |
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