<?xml version="1.0" encoding="utf-8"?>
<!--
  Copyright 2012 Eric Niebler

  Distributed under the Boost
  Software License, Version 1.0. (See accompanying
  file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
  -->
<header name="boost/proto/matches.hpp">
  <para>
    Contains definition of the
    <computeroutput>
      <classname alt="boost::proto::matches">proto::matches&lt;&gt;</classname>
    </computeroutput>
    metafunction for determining if a given expression matches a given pattern.
  </para>
  <namespace name="boost">
    <namespace name="proto">
      <struct name="_">
        <inherit><type><classname>proto::transform</classname>&lt;_&gt;</type></inherit>
        <purpose>A wildcard grammar element that matches any expression, and a transform that returns
          the current expression unchanged.</purpose>
        <description>
          <para>
            The wildcard type, <computeroutput>proto::_</computeroutput>, is a grammar element such
            that <computeroutput><classname>proto::matches</classname>&lt;E, proto::_&gt;::value</computeroutput>
            is <computeroutput>true</computeroutput> for any expression type <computeroutput>E</computeroutput>.
          </para>
          <para>
            The wildcard can also be used as a stand-in for a template argument when matching terminals.
            For instance, the following is a grammar that will match any
            <computeroutput>std::complex&lt;&gt;</computeroutput> terminal:<programlisting>BOOST_MPL_ASSERT((
  <classname>proto::matches</classname>&lt;
    <classname>proto::terminal</classname>&lt;std::complex&lt;double&gt; &gt;::type,
    <emphasis role="bold"><classname>proto::terminal</classname>&lt;std::complex&lt; proto::_ &gt; &gt;</emphasis>
  &gt;
));</programlisting>
          </para>
          <para>
            When used as a transform, <computeroutput>proto::_</computeroutput> returns the current expression
            unchanged. For instance, in the following, <computeroutput>proto::_</computeroutput> is used with
            the <computeroutput><classname alt="proto::fold">proto::fold&lt;&gt;</classname></computeroutput>
            transform to fold the children of a node:<programlisting>struct CountChildren :
  <classname>proto::or_</classname>&lt;
    // Terminals have no children
    <classname>proto::when</classname>&lt;<classname>proto::terminal</classname>&lt;proto::_&gt;, mpl::int_&lt;0&gt;()&gt;,
    // Use proto::fold&lt;&gt; to count the children of non-terminals
    <classname>proto::otherwise</classname>&lt;
      <classname>proto::fold</classname>&lt;
        proto::_, // &lt;-- fold the current expression
        mpl::int_&lt;0&gt;(),
        mpl::plus&lt;<classname>proto::_state</classname>, mpl::int_&lt;1&gt; &gt;()
      &gt;
    &gt;
  &gt;
{};</programlisting>
          </para>
        </description>
        <struct name="impl">
          <template>
            <template-type-parameter name="Expr"/>
            <template-type-parameter name="State"/>
            <template-type-parameter name="Data"/>
          </template>
          <inherit><type><classname>proto::transform_impl</classname>&lt;Expr, State, Data&gt;</type></inherit>
          <typedef name="result_type">
            <type>Expr</type>
          </typedef>
          <method-group name="public member functions">
            <method name="operator()" cv="const">
              <type>Expr</type>
              <parameter name="expr">
                <paramtype>typename impl::expr_param</paramtype>
                <description>
                  <para>An expression </para>
                </description>
              </parameter>
              <parameter name="">
                <paramtype>typename impl::state_param</paramtype>
              </parameter>
              <parameter name="">
                <paramtype>typename impl::data_param</paramtype>
              </parameter>
              <returns>
                <para>
                  <computeroutput>expr</computeroutput>
                </para>
              </returns>
            </method>
          </method-group>
        </struct>
        <typedef name="proto_grammar">
          <type>_</type>
        </typedef>
      </struct>

      <!-- proto::not_ -->
      <struct name="not_">
        <template>
          <template-type-parameter name="Grammar"/>
        </template>
        <inherit><type><classname>proto::transform</classname>&lt;not_&lt;Grammar&gt; &gt;</type></inherit>
        <purpose>Inverts the set of expressions matched by a grammar. When used as a transform,
          <computeroutput>proto::not_&lt;&gt;</computeroutput> returns the current expression unchanged.
        </purpose>
        <description>
          <para>
            If an expression type <computeroutput>E</computeroutput> does not match a grammar
            <computeroutput>G</computeroutput>, then <computeroutput>E</computeroutput> <emphasis>does</emphasis>
            match <computeroutput>proto::not_&lt;G&gt;</computeroutput>. For example,
            <computeroutput><classname>proto::not_</classname>&lt;<classname>proto::terminal</classname>&lt;<classname>proto::_</classname>&gt; &gt;</computeroutput>
            will match any non-terminal.
          </para>
        </description>
        <struct name="impl">
          <template>
            <template-type-parameter name="Expr"/>
            <template-type-parameter name="State"/>
            <template-type-parameter name="Data"/>
          </template>
          <inherit><type><classname>proto::transform_impl</classname>&lt;Expr, State, Data&gt;</type></inherit>
          <typedef name="result_type">
            <type>Expr</type>
          </typedef>
          <method-group name="public member functions">
            <method name="operator()" cv="const">
              <type>Expr</type>
              <parameter name="expr">
                <paramtype>typename impl::expr_param</paramtype>
                <description>
                  <para>An expression </para>
                </description>
              </parameter>
              <parameter name="">
                <paramtype>typename impl::state_param</paramtype>
              </parameter>
              <parameter name="">
                <paramtype>typename impl::data_param</paramtype>
              </parameter>
              <requires>
                <para>
                  <computeroutput><classname>proto::matches</classname>&lt;Expr, proto::not_&gt;::value</computeroutput>
                  is <computeroutput>true</computeroutput>.
                </para>
              </requires>
              <returns>
                <para>
                  <computeroutput>expr</computeroutput>
                </para>
              </returns>
            </method>
          </method-group>
        </struct>
        <typedef name="proto_grammar">
          <type>not_</type>
        </typedef>
      </struct>

      <!-- proto::if_ -->
      <struct name="if_">
        <template>
          <template-type-parameter name="If"/>
          <template-type-parameter name="Then">
            <default><type><classname>proto::_</classname></type></default>
          </template-type-parameter>
          <template-type-parameter name="Else">
            <default><type><classname>proto::not_</classname>&lt;<classname>proto::_</classname>&gt;</type></default>
          </template-type-parameter>
        </template>
        <inherit><classname>proto::transform</classname>&lt;if_&lt;If, Then, Else&gt; &gt;</inherit>
        <purpose>Used to select one grammar or another based on the result of a compile-time Boolean.
          When used as a transform, <computeroutput>proto::if_&lt;&gt;</computeroutput> selects between two
          transforms based on a compile-time Boolean.</purpose>
        <description>
          <para>
            When <computeroutput>proto::if_&lt;If, Then, Else&gt;</computeroutput> is used as a grammar,
            <computeroutput>If</computeroutput> must be a Proto transform and
            <computeroutput>Then</computeroutput> and <computeroutput>Else</computeroutput> must be grammars.
            An expression type <computeroutput>E</computeroutput> matches
            <computeroutput>proto::if_&lt;If, Then, Else&gt;</computeroutput> if
            <computeroutput>boost::result_of&lt;<classname>proto::when</classname>&lt;<classname>proto::_</classname>, If&gt;(E)&gt;::type::value</computeroutput>
            is <computeroutput>true</computeroutput> and
            <computeroutput>E</computeroutput> matches <computeroutput>Then</computeroutput>; or, if
            <computeroutput>boost::result_of&lt;<classname>proto::when</classname>&lt;<classname>proto::_</classname>, If&gt;(E)&gt;::type::value</computeroutput>
            is <computeroutput>false</computeroutput> and <computeroutput>E</computeroutput> matches <computeroutput>Else</computeroutput>.
          </para>
          <para>
            The template parameter <computeroutput>Then</computeroutput> defaults to <computeroutput><classname>proto::_</classname></computeroutput>
            and <computeroutput>Else</computeroutput> defaults to
            <computeroutput><classname>proto::not_</classname>&lt;<classname>proto::_</classname>&gt;</computeroutput>,
            so an expression type <computeroutput>E</computeroutput> will match
            <computeroutput>proto::if_&lt;If&gt;</computeroutput> if and only if
            <computeroutput>boost::result_of&lt;<classname>proto::when</classname>&lt;<classname>proto::_</classname>, If&gt;(E)&gt;::type::value</computeroutput>
            is <computeroutput>true</computeroutput>.
          </para>
          <para>
            <programlisting>// A grammar that only matches integral terminals,
// using is_integral&lt;&gt; from Boost.Type_traits.
struct IsIntegral :
  <classname>proto::and_</classname>&lt;
    <classname>proto::terminal</classname>&lt;<classname>proto::_</classname>&gt;,
    <classname>proto::if_</classname>&lt; boost::is_integral&lt;<classname>proto::_value</classname>&gt;()&gt;
  &gt;
{};</programlisting>
          </para>
          <para>
            When <computeroutput>proto::if_&lt;If, Then, Else&gt;</computeroutput> is used as a transform,
            <computeroutput>If</computeroutput>, <computeroutput>Then</computeroutput> and
            <computeroutput>Else</computeroutput> must be Proto transforms. When applying the transform to
            an expression <computeroutput>E</computeroutput>, state <computeroutput>S</computeroutput> and
            data <computeroutput>V</computeroutput>, if
            <computeroutput>boost::result_of&lt;<classname>proto::when</classname>&lt;<classname>proto::_</classname>, If&gt;(E,S,V)&gt;::type::value</computeroutput>
            is <computeroutput>true</computeroutput> then the <computeroutput>Then</computeroutput> transform
            is applied; otherwise the <computeroutput>Else</computeroutput> transform is applied.
            <programlisting>// Match a terminal. If the terminal is integral, return
// mpl::true_; otherwise, return mpl::false_.
struct IsIntegral2 :
  <classname>proto::when</classname>&lt;
    <classname>proto::terminal</classname>&lt;_&gt;,
    proto::if_&lt;
      boost::is_integral&lt;<classname>proto::_value</classname>&gt;(),
      mpl::true_(),
      mpl::false_()
    &gt;
  &gt;
{};</programlisting>
          </para>
        </description>
        <struct name="impl">
          <template>
            <template-type-parameter name="Expr"/>
            <template-type-parameter name="State"/>
            <template-type-parameter name="Data"/>
          </template>
          <inherit><type><classname>proto::transform_impl</classname>&lt; Expr, State, Data &gt;</type></inherit>
          <typedef name="result_type">
            <type>typename mpl::if_&lt;
      typename boost::result_of&lt;<classname>proto::when</classname>&lt;<classname>proto::_</classname>, If&gt;(Expr, State, Data)&gt;::type,
      typename boost::result_of&lt;<classname>proto::when</classname>&lt;<classname>proto::_</classname>, Then&gt;(Expr, State, Data)&gt;::type,
      typename boost::result_of&lt;<classname>proto::when</classname>&lt;<classname>proto::_</classname>, Else&gt;(Expr, State, Data)&gt;::type
    &gt;::type</type>
          </typedef>
          <method-group name="public member functions">
            <method name="operator()" cv="const">
              <type>result_type</type>
              <parameter name="expr">
                <paramtype>typename impl::expr_param</paramtype>
                <description>
                  <para>An expression </para>
                </description>
              </parameter>
              <parameter name="state">
                <paramtype>typename impl::state_param</paramtype>
                <description>
                  <para>The current state </para>
                </description>
              </parameter>
              <parameter name="data">
                <paramtype>typename impl::data_param</paramtype>
                <description>
                  <para>A data of arbitrary type </para>
                </description>
              </parameter>
              <returns>
                <para>
                  <computeroutput><classname>proto::when</classname>&lt;<classname>proto::_</classname>, <replaceable>Then-or-Else</replaceable>&gt;()(expr, state, data)</computeroutput>
                </para>
              </returns>
            </method>
          </method-group>
        </struct>
        <typedef name="proto_grammar">
          <type>if_</type>
        </typedef>
      </struct>

      <!-- proto::or_ -->
      <struct name="or_">
        <template>
          <template-type-parameter name="G" pack="1"/>
        </template>
        <inherit><type><classname>proto::transform</classname>&lt;or_&lt;G...&gt; &gt;</type></inherit>
        <purpose>For matching one of a set of alternate grammars. Alternates are tried in order to avoid ambiguity.
          When used as a transform, <computeroutput>proto::or_&lt;&gt;</computeroutput> applies the transform
          associated with the first grammar that matches the expression.</purpose>
        <description>
          <para>
            An expression type <computeroutput>E</computeroutput> matches
            <computeroutput>proto::or_&lt;G<subscript>0</subscript>,G<subscript>1</subscript>,...G<subscript>n</subscript>&gt;</computeroutput>
            if <computeroutput>E</computeroutput> matches any <computeroutput>G<subscript>x</subscript></computeroutput> for
            <computeroutput>x</computeroutput> in <computeroutput>[0,n]</computeroutput>.
          </para>
          <para>
            When applying
            <computeroutput>proto::or_&lt;G<subscript>0</subscript>,G<subscript>1</subscript>,...G<subscript>n</subscript>&gt;</computeroutput>
            as a transform with an expression <computeroutput>e</computeroutput> of type <computeroutput>E</computeroutput>,
            state <computeroutput>s</computeroutput> and data <computeroutput>d</computeroutput>, it is equivalent to
            <computeroutput>G<subscript>x</subscript>()(e, s, d)</computeroutput>, where
            <computeroutput>x</computeroutput> is the lowest number such that
            <computeroutput><classname>proto::matches</classname>&lt;E, G<subscript>x</subscript>&gt;::value</computeroutput>
            is <computeroutput>true</computeroutput>.
          </para>
          <para>
            The maximun number of template arguments <computeroutput>proto::or_&lt;&gt;</computeroutput> accepts
            is controlled by the <computeroutput><macroname>BOOST_PROTO_MAX_LOGICAL_ARITY</macroname></computeroutput>
            macro.
          </para>
        </description>
        <struct name="impl">
          <template>
            <template-type-parameter name="Expr"/>
            <template-type-parameter name="State"/>
            <template-type-parameter name="Data"/>
          </template>
          <inherit><type><classname>proto::transform_impl</classname>&lt; Expr, State, Data &gt;</type></inherit>
          <typedef name="result_type">
            <type><replaceable>unspecified</replaceable></type>
          </typedef>
          <method-group name="public member functions">
            <method name="operator()" cv="const">
              <type>result_type</type>
              <parameter name="expr">
                <paramtype>typename impl::expr_param</paramtype>
                <description>
                  <para>An expression </para>
                </description>
              </parameter>
              <parameter name="state">
                <paramtype>typename impl::state_param</paramtype>
                <description>
                  <para>The current state </para>
                </description>
              </parameter>
              <parameter name="data">
                <paramtype>typename impl::data_param</paramtype>
                <description>
                  <para>A data of arbitrary type </para>
                </description>
              </parameter>
              <returns>
                <para>
                  <computeroutput>
                    G<subscript>x</subscript>()(expr, state, data)
                  </computeroutput>, where
                  <computeroutput>x</computeroutput> is the lowest number such that
                  <computeroutput>
                    <classname>proto::matches</classname>&lt;Expr, G<subscript>x</subscript>&gt;::value
                  </computeroutput>
                  is <computeroutput>true</computeroutput>.
                </para>
              </returns>
            </method>
          </method-group>
        </struct>
        <typedef name="proto_grammar">
          <type>or_</type>
        </typedef>
      </struct>

      <!-- proto::and_ -->
      <struct name="and_">
        <template>
          <template-type-parameter name="G" pack="1"/>
        </template>
        <inherit><type><classname>proto::transform</classname>&lt;and_&lt;G...&gt; &gt;</type></inherit>
        <purpose>For matching all of a set of grammars. When used as a transform,
          <computeroutput>proto::and_&lt;&gt;</computeroutput> applies the transform associated
          with each grammar in the set and returns the result of the last.</purpose>
        <description>
          <para>
            An expression type <computeroutput>E</computeroutput> matches
            <computeroutput>proto::and_&lt;G<subscript>0</subscript>,G<subscript>1</subscript>,...G<subscript>n</subscript>&gt;</computeroutput>
            if <computeroutput>E</computeroutput> matches all <computeroutput>G<subscript>x</subscript></computeroutput>
            for <computeroutput>x</computeroutput> in <computeroutput>[0,n]</computeroutput>.
          </para>
          <para>
            When applying
            <computeroutput>proto::and_&lt;G<subscript>0</subscript>,G<subscript>1</subscript>,...G<subscript>n</subscript>&gt;</computeroutput>
            as a transform with an expression <computeroutput>e</computeroutput>, state
            <computeroutput>s</computeroutput> and data <computeroutput>d</computeroutput>, it is equivalent
            to <computeroutput>(G<subscript>0</subscript>()(e, s, d),G<subscript>1</subscript>()(e, s, d),...G<subscript>n</subscript>()(e, s, d))</computeroutput>.
          </para>
          <para>
            The maximun number of template arguments <computeroutput>proto::and_&lt;&gt;</computeroutput> accepts
            is controlled by the <computeroutput><macroname>BOOST_PROTO_MAX_LOGICAL_ARITY</macroname></computeroutput>
            macro.
          </para>
        </description>
        <struct name="impl">
          <template>
            <template-type-parameter name="Expr"/>
            <template-type-parameter name="State"/>
            <template-type-parameter name="Data"/>
          </template>
          <inherit><type><classname>proto::transform_impl</classname>&lt; Expr, State, Data &gt;</type></inherit>
          <typedef name="result_type">
            <type>typename boost::result_of&lt;G<subscript>n</subscript>(Expr, State, Data)&gt;::type</type>
          </typedef>
          <method-group name="public member functions">
            <method name="operator()" cv="const">
              <type>result_type</type>
              <parameter name="expr">
                <paramtype>typename impl::expr_param</paramtype>
                <description>
                  <para>An expression </para>
                </description>
              </parameter>
              <parameter name="state">
                <paramtype>typename impl::state_param</paramtype>
                <description>
                  <para>The current state </para>
                </description>
              </parameter>
              <parameter name="data">
                <paramtype>typename impl::data_param</paramtype>
                <description>
                  <para>A data of arbitrary type </para>
                </description>
              </parameter>
              <returns>
                <para>
                  <computeroutput>(G<subscript>0</subscript>()(expr, state, data),G<subscript>1</subscript>()(expr, state, data),...G<subscript>n</subscript>()(expr, state, data))</computeroutput>
                </para>
              </returns>
            </method>
          </method-group>
        </struct>
        <typedef name="proto_grammar">
          <type>and_</type>
        </typedef>
      </struct>

      <!-- proto::switch_ -->
      <struct name="switch_">
        <template>
          <template-type-parameter name="Cases"/>
          <template-type-parameter name="Transform"/>
        </template>
        <inherit><classname>proto::transform</classname>&lt;switch_&lt;Cases, Transform&gt; &gt;</inherit>
        <purpose>For matching one of a set of alternate grammars, which are looked up based on
          the result type of the transform passed in second template parameter. 
          If no transform is passed, the default one is <computeroutput><classname>proto::tag_of</classname>&lt;<classname>proto::_</classname>&gt;()</computeroutput>
          so the default matching is based on the expression's tag type. When used as a transform,
          <computeroutput>proto::switch_&lt;&gt;</computeroutput> applies the transform associated
          with the sub-grammar that matches the expression.</purpose>
        <description>
        <para>
          An expression type <computeroutput>E</computeroutput> matches
            <computeroutput>proto::switch_&lt;C,T&gt;</computeroutput> if
          <computeroutput>E</computeroutput> matches
            <computeroutput>C::case_&lt;boost::result_of&lt;<classname>proto::when</classname>&lt;<classname>proto::_</classname>,T&gt;(E)&gt;::type&gt;</computeroutput>.
          </para>
        <para>
          When applying <computeroutput>proto::switch_&lt;C,T&gt;</computeroutput> as a
            transform with an expression <computeroutput>e</computeroutput> of type
            <computeroutput>E</computeroutput>, state <computeroutput>s</computeroutput> of
            type <computeroutput>S</computeroutput> and data <computeroutput>d</computeroutput>
            of type <computeroutput>D</computeroutput>, it is equivalent to
            <computeroutput>C::case_&lt;boost::result_of&lt;<classname>proto::when</classname>&lt;<classname>proto::_</classname>,T&gt;(E,S,D)&gt;::type&gt;()(e, s, d)</computeroutput>.
          </para>
        </description>
        <struct name="impl">
          <template>
            <template-type-parameter name="Expr"/>
            <template-type-parameter name="State"/>
            <template-type-parameter name="Data"/>
          </template>
          <inherit><type>
    Cases::template case_&lt;
      typename <classname>when</classname>&lt;_, Transform&gt;::template impl&lt;Expr, State, Data&gt;::result_type 
    &gt;::template impl&lt;Expr, State, Data&gt;</type>
          </inherit>
        </struct>
        <typedef name="proto_grammar">
          <type>switch_</type>
        </typedef>
      </struct>

      <!-- proto::exact -->
      <struct name="exact">
        <template>
          <template-type-parameter name="T"/>
        </template>
        <purpose>For forcing exact matches of terminal types.</purpose>
        <description>
          <para>By default, matching terminals ignores references and cv-qualifiers. For instance,
            a terminal expression of type
            <computeroutput><classname>proto::terminal</classname>&lt;int const &amp;&gt;::type</computeroutput>
            will match the grammar <computeroutput><classname>proto::terminal</classname>&lt;int&gt;</computeroutput>.
            If that is not desired, you can force an exact match with
            <computeroutput><classname>proto::terminal</classname>&lt;proto::exact&lt;int&gt; &gt;</computeroutput>.
            This will only match integer terminals where the terminal is held by value.</para>
        </description>
      </struct>

      <!-- proto::convertible_to -->
      <struct name="convertible_to">
        <template>
          <template-type-parameter name="T"/>
        </template>
        <purpose>For matching terminals that are convertible to a type.</purpose>
        <description>
          <para>
            Use <computeroutput>proto::convertible_to&lt;&gt;</computeroutput> to match a terminal that is
            convertible to some type. For example, the grammar
            <computeroutput><classname>proto::terminal</classname>&lt;proto::convertible_to&lt;int&gt; &gt;</computeroutput>
            will match any terminal whose argument is convertible to an integer.
          </para>
        </description>
      </struct>
      
      <!-- proto::vararg -->
      <struct name="vararg">
        <template>
          <template-type-parameter name="Grammar"/>
        </template>
        <purpose>For matching a Grammar to a variable number of sub-expressions.</purpose>
        <description>
          <para>
            An expression type <computeroutput><classname>proto::basic_expr</classname>&lt;AT,
            <classname alt="proto::listN">proto::list<replaceable>N</replaceable></classname>&lt;A<subscript>0</subscript>,...A<subscript>n</subscript>,U<subscript>0</subscript>,...U<subscript>m</subscript>&gt; &gt;</computeroutput>
            matches a grammar <computeroutput><classname>proto::basic_expr</classname>&lt;BT,
            <classname alt="proto::listN">proto::list<replaceable>M</replaceable></classname>&lt;B<subscript>0</subscript>,...B<subscript>n</subscript>,proto::vararg&lt;V&gt; &gt; &gt;</computeroutput>
            if <computeroutput>BT</computeroutput> is <computeroutput><classname>proto::_</classname></computeroutput>
            or <computeroutput>AT</computeroutput>, and if
            <computeroutput>A<subscript>x</subscript></computeroutput> matches
            <computeroutput>B<subscript>x</subscript></computeroutput>
            for each <computeroutput>x</computeroutput> in <computeroutput>[0,n]</computeroutput>
            and if <computeroutput>U<subscript>x</subscript></computeroutput> matches
            <computeroutput>V</computeroutput> for each <computeroutput>x</computeroutput> in <computeroutput>[0,m]</computeroutput>.
          </para>
          <para>For example:</para>
          <para>
            <programlisting>// Match any function call expression, regardless
// of the number of function arguments:
struct Function :
  <classname>proto::function</classname>&lt; proto::vararg&lt;proto::_&gt; &gt;
{};</programlisting>
          </para>
          <para>
            When used as a transform, <computeroutput>proto::vararg&lt;G&gt;</computeroutput>
            applies <computeroutput>G</computeroutput>'s transform.
          </para>
        </description>
      </struct>

      <!-- proto::matches -->
      <struct name="matches">
        <template>
          <template-type-parameter name="Expr"/>
          <template-type-parameter name="Grammar"/>
        </template>
        <purpose>A Boolean metafunction that evaluates whether a given expression type matches a grammar.</purpose>
        <description>
          <para>
            <computeroutput>proto::matches&lt;Expr, Grammar&gt;</computeroutput> inherits from
            <computeroutput>mpl::true_</computeroutput> if
            <computeroutput>Expr::proto_grammar</computeroutput> matches
            <computeroutput>Grammar::proto_grammar</computeroutput>, and from
            <computeroutput>mpl::false_</computeroutput> otherwise.
          </para>
          <para>
            Non-terminal expressions are matched against a grammar according to the following rules:
            <itemizedlist>
              <listitem>
                <para>
                  The wildcard pattern, <computeroutput>
                    <classname>proto::_</classname>
                  </computeroutput>, matches any expression.
                </para>
              </listitem>
              <listitem>
                <para>
                  An expression
                  <computeroutput>
                    <classname>proto::basic_expr</classname>&lt;AT,
                    <classname alt="proto::listN">
                      proto::list<replaceable>N</replaceable>
                    </classname>&lt;A<subscript>0</subscript>,...A<subscript>n</subscript>&gt;
                    &gt;
                  </computeroutput>
                  matches a grammar
                  <computeroutput>
                    <classname>proto::basic_expr</classname>&lt;BT,
                    <classname alt="proto::listN">
                      proto::list<replaceable>N</replaceable>
                    </classname>&lt;B<subscript>0</subscript>,...B<subscript>n</subscript>&gt;
                    &gt;
                  </computeroutput> if
                  <computeroutput>BT</computeroutput> is <computeroutput>
                    <classname>proto::_</classname>
                  </computeroutput> or
                  <computeroutput>AT</computeroutput>, and if <computeroutput>
                    A<subscript>x</subscript>
                  </computeroutput> matches
                  <computeroutput>
                    B<subscript>x</subscript>
                  </computeroutput> for each <computeroutput>x</computeroutput> in <computeroutput>[0,n]</computeroutput>.
                </para>
              </listitem>
              <listitem>
                <para>
                  An expression
                  <computeroutput>
                    <classname>proto::basic_expr</classname>&lt;AT,
                    <classname alt="proto::listN">
                      proto::list<replaceable>N</replaceable>
                    </classname>&lt;A<subscript>0</subscript>,...A<subscript>n</subscript>,U<subscript>0</subscript>,...U<subscript>m</subscript>&gt;
                    &gt;
                  </computeroutput> matches a grammar
                  <computeroutput>
                    <classname>proto::basic_expr</classname>&lt;BT,
                    <classname alt="proto::listN">
                      proto::list<replaceable>M</replaceable>
                    </classname>&lt;B<subscript>0</subscript>,...B<subscript>n</subscript>,<classname>proto::vararg</classname>&lt;V&gt;
                    &gt; &gt;
                  </computeroutput> if
                  <computeroutput>BT</computeroutput> is <computeroutput>
                    <classname>proto::_</classname>
                  </computeroutput> or
                  <computeroutput>AT</computeroutput>, and if
                  <computeroutput>
                    A<subscript>x</subscript>
                  </computeroutput> matches
                  <computeroutput>
                    B<subscript>x</subscript>
                  </computeroutput> for each
                  <computeroutput>x</computeroutput> in <computeroutput>[0,n]</computeroutput> and if
                  <computeroutput>
                    U<subscript>x</subscript>
                  </computeroutput> matches
                  <computeroutput>V</computeroutput> for each <computeroutput>x</computeroutput> in
                  <computeroutput>[0,m]</computeroutput>.
                </para>
              </listitem>
              <listitem>
                <para>
                  An expression <computeroutput>E</computeroutput> matches
                  <computeroutput>
                    <classname>proto::or_</classname>&lt;B<subscript>0</subscript>,...B<subscript>n</subscript>&gt;
                  </computeroutput> if
                  <computeroutput>E</computeroutput> matches some
                  <computeroutput>
                    B<subscript>x</subscript>
                  </computeroutput> for
                  <computeroutput>x</computeroutput> in <computeroutput>[0,n]</computeroutput>.
                </para>
              </listitem>
              <listitem>
                <para>
                  An expression <computeroutput>E</computeroutput> matches
                  <computeroutput>
                    <classname>proto::and_</classname>&lt;B<subscript>0</subscript>,...B<subscript>n</subscript>&gt;
                  </computeroutput> if
                  <computeroutput>E</computeroutput> matches all
                  <computeroutput>
                    B<subscript>x</subscript>
                  </computeroutput> for
                  <computeroutput>x</computeroutput> in <computeroutput>[0,n]</computeroutput>.
                </para>
              </listitem>
              <listitem>
                <para>
                  An expression <computeroutput>E</computeroutput> matches
                  <computeroutput>
                    <classname>proto::if_</classname>&lt;T,U,V&gt;
                  </computeroutput> if:
                  <itemizedlist>
                    <listitem>
                      <computeroutput>
                        boost::result_of&lt;<classname>proto::when</classname>&lt;<classname>proto::_</classname>,T&gt;(E)&gt;::type::value
                      </computeroutput>
                      is <computeroutput>true</computeroutput> and
                      <computeroutput>E</computeroutput> matches
                      <computeroutput>U</computeroutput>, <emphasis>or</emphasis>
                    </listitem>
                    <listitem>
                      <computeroutput>
                        boost::result_of&lt;<classname>proto::when</classname>&lt;<classname>proto::_</classname>,T&gt;(E)&gt;::type::value
                      </computeroutput>
                      is <computeroutput>false</computeroutput> and <computeroutput>E</computeroutput> matches
                      <computeroutput>V</computeroutput>.
                    </listitem>
                  </itemizedlist>
                  Note: <computeroutput>U</computeroutput> defaults to <computeroutput>
                    <classname>proto::_</classname>
                  </computeroutput>
                  and <computeroutput>V</computeroutput> defaults to
                  <computeroutput>
                    <classname>proto::not_</classname>&lt;<classname>proto::_</classname>&gt;
                  </computeroutput>.
                </para>
              </listitem>
              <listitem>
                <para>
                  An expression <computeroutput>E</computeroutput> matches
                  <computeroutput>
                    <classname>proto::not_</classname>&lt;T&gt;
                  </computeroutput> if
                  <computeroutput>E</computeroutput> does <emphasis>not</emphasis> match <computeroutput>T</computeroutput>.
                </para>
              </listitem>
              <listitem>
                <para>
                  An expression <computeroutput>E</computeroutput> matches
                  <computeroutput>
                    <classname>proto::switch_</classname>&lt;C, T&gt;
                  </computeroutput> if
                  <computeroutput>E</computeroutput> matches <computeroutput>C::case_&lt;boost::result_of&lt;<classname>proto::when</classname>&lt;<classname>proto::_</classname>,T&gt;(E)&gt;::type&gt;</computeroutput>.
                  Note: <computeroutput>T</computeroutput> defaults to <computeroutput><classname>proto::tag_of</classname>&lt;<classname>proto::_</classname>&gt;()</computeroutput>
                </para>
              </listitem>
            </itemizedlist>
          </para>
          <para>
            A terminal expression can trivially match the grammar <classname>proto::_</classname>. In addition,
            a terminal expression
            <computeroutput>
              <classname>proto::basic_expr</classname>&lt;AT,
              <classname>proto::term</classname>&lt;A&gt; &gt;
            </computeroutput> matches a grammar
            <computeroutput>
              <classname>proto::basic_expr</classname>&lt;BT, <classname>proto::term</classname>&lt;B&gt; &gt;
            </computeroutput>
            if <computeroutput>BT</computeroutput> is <computeroutput><classname>proto::_</classname></computeroutput>
            or <computeroutput>AT</computeroutput> and one of the following is true:
            <itemizedlist>
              <listitem>
                <para>
                  <computeroutput>B</computeroutput> is the wildcard pattern,
                  <computeroutput>
                    <classname>proto::_</classname>
                  </computeroutput>
                </para>
              </listitem>
              <listitem>
                <para>
                  <computeroutput>A</computeroutput> is <computeroutput>B</computeroutput>
                </para>
              </listitem>
              <listitem>
                <para>
                  <computeroutput>A</computeroutput> is <computeroutput>B &amp;</computeroutput>
                </para>
              </listitem>
              <listitem>
                <para>
                  <computeroutput>A</computeroutput> is <computeroutput>B const &amp;</computeroutput>
                </para>
              </listitem>
              <listitem>
                <para>
                  <computeroutput>B</computeroutput> is <computeroutput>
                    <classname>proto::exact</classname>&lt;A&gt;
                  </computeroutput>
                </para>
              </listitem>
              <listitem>
                <para>
                  <computeroutput>B</computeroutput> is
                  <computeroutput>
                    <classname>proto::convertible_to</classname>&lt;X&gt;
                  </computeroutput>
                  and <computeroutput>boost::is_convertible&lt;A,X&gt;::value</computeroutput> is
                  <computeroutput>true</computeroutput>.
                </para>
              </listitem>
              <listitem>
                <para>
                  <computeroutput>A</computeroutput> is <computeroutput>X[M]</computeroutput> or
                  <computeroutput>X(&amp;)[M]</computeroutput> and
                  <computeroutput>B</computeroutput> is <computeroutput>
                    X[<globalname>proto::N</globalname>]
                  </computeroutput>.
                </para>
              </listitem>
              <listitem>
                <para>
                  <computeroutput>A</computeroutput> is <computeroutput>X(&amp;)[M]</computeroutput>
                  and <computeroutput>B</computeroutput> is <computeroutput>
                    X(&amp;)[<globalname>proto::N</globalname>]
                  </computeroutput>.
                </para>
              </listitem>
              <listitem>
                <para>
                  <computeroutput>A</computeroutput> is <computeroutput>X[M]</computeroutput> or
                  <computeroutput>X(&amp;)[M]</computeroutput> and <computeroutput>B</computeroutput> is
                  <computeroutput>X*</computeroutput>.
                </para>
              </listitem>
              <listitem>
                <para>
                  <computeroutput>B</computeroutput> <replaceable>lambda-matches</replaceable>
                  <computeroutput>A</computeroutput> (see below).
                </para>
              </listitem>
            </itemizedlist>
          </para>
          <para>
            A type <computeroutput>B</computeroutput> <replaceable>lambda-matches</replaceable>
            <computeroutput>A</computeroutput> if one of the following is true:
            <itemizedlist>
              <listitem>
                <para>
                  <computeroutput>B</computeroutput> is <computeroutput>A</computeroutput>
                </para>
              </listitem>
              <listitem>
                <para>
                  <computeroutput>B</computeroutput> is the wildcard pattern, <computeroutput>
                    <classname>proto::_</classname>
                  </computeroutput>
                </para>
              </listitem>
              <listitem>
                <para>
                  <computeroutput>B</computeroutput> is <computeroutput>
                    T&lt;B<subscript>0</subscript>,...B<subscript>n</subscript>&gt;
                  </computeroutput> and <computeroutput>A</computeroutput> is <computeroutput>
                    T&lt;A<subscript>0</subscript>,...A<subscript>n</subscript>&gt;
                  </computeroutput> and for each <computeroutput>x</computeroutput> in <computeroutput>[0,n]</computeroutput>,
                  <computeroutput>A<subscript>x</subscript></computeroutput> and
                  <computeroutput>B<subscript>x</subscript></computeroutput> are types such that
                  <computeroutput>A<subscript>x</subscript></computeroutput> <replaceable>lambda-matches</replaceable>
                  <computeroutput>B<subscript>x</subscript></computeroutput>
                </para>
              </listitem>
            </itemizedlist>
          </para>
        </description>
        <inherit>
          <type>mpl::bool_&lt;<replaceable>true-or-false</replaceable>&gt;</type></inherit>
      </struct>
    </namespace>
  </namespace>
</header>