<?xml version="1.0" encoding="utf-8"?>
<header name="boost/proto/domain.hpp">
  <para>
    Contains definition of <computeroutput><classname alt="boost::proto::domain">proto::domain&lt;&gt;</classname>
    </computeroutput> class template and helpers for defining domains with a generator and a grammar for controlling
    operator overloading.
  </para>
  <namespace name="boost">
    <namespace name="proto">

      <!-- proto::domain<> -->
      <struct name="domain">
        <template>
          <template-type-parameter name="Generator">
            <default><classname>proto::default_generator</classname></default>
          </template-type-parameter>
          <template-type-parameter name="Grammar">
            <default><classname>proto::_</classname></default>
          </template-type-parameter>
        </template>
        <inherit><type>Generator</type></inherit>
        <purpose>For use in defining domain tags to be used with <computeroutput>
          <classname alt="proto::extends">proto::extends&lt;&gt;</classname></computeroutput>. A
          <emphasis>domain</emphasis> associates an expression type with a <emphasis>generator</emphasis>,
          and optionally a <emphasis>grammar</emphasis>.
        </purpose>
        <description>
          <para>
            The Generator determines how new expressions in the domain are constructed. Typically, a generator
            wraps all new expressions in a wrapper that imparts domain-specific behaviors to expressions within
            its domain. (See <computeroutput><classname alt="proto::extends">proto::extends&lt;&gt;</classname></computeroutput>.)
          </para>
          <para>
            The Grammar determines whether a given expression is valid within the domain, and automatically
            disables any operator overloads which would cause an invalid expression to be created. By default,
            the Grammar parameter defaults to the wildcard, <computeroutput><classname>proto::_</classname>
            </computeroutput>, which makes all expressions valid within the domain.
          </para>
          <para>
            Example: <programlisting> template&lt;typename Expr&gt;
 struct MyExpr;

 struct MyGrammar
   : <classname>proto::or_</classname>&lt; <classname>proto::terminal</classname>&lt;_&gt;, <classname>proto::plus</classname>&lt;MyGrammar, MyGrammar&gt; &gt;
 {};

 // Define MyDomain, in which all expressions are
 // wrapped in MyExpr&lt;&gt; and only expressions that
 // conform to MyGrammar are allowed.
 struct MyDomain
   : <classname>proto::domain</classname>&lt;<classname>proto::generator</classname>&lt;MyExpr&gt;, MyGrammar&gt;
 {};

 // Use MyDomain to define MyExpr
 template&lt;typename Expr&gt;
 struct MyExpr
   : <classname>proto::extends</classname>&lt;Expr, MyExpr&lt;Expr&gt;, MyDomain&gt;
 {
     // ...
 };
            </programlisting>
          </para>
        </description>
        <typedef name="proto_grammar">
          <type>Grammar</type>
        </typedef>
        <typedef name="proto_generator">
          <type>Generator</type>
        </typedef>
      </struct>

      <!-- proto::default_domain -->
      <struct name="default_domain">
        <inherit><classname>proto::domain</classname>&lt;&gt;</inherit>
        <purpose>The domain expressions have by default, if <computeroutput>
          <classname alt="proto::extends">proto::extends&lt;&gt;</classname></computeroutput> has not been used
          to associate a domain with an expression.</purpose>
      </struct>

      <!-- proto::deduce_domain -->
      <struct name="deduce_domain">
        <purpose>A pseudo-domain for use in functions and metafunctions that require a domain parameter.
          It indicates that the domain of the parent node should be inferred from the domains of the child nodes.</purpose>
      </struct>

      <!-- proto::is_domain -->
      <struct name="is_domain">
        <template>
          <template-type-parameter name="T"/>
        </template>
        <inherit>
          <type>mpl::bool_&lt; <replaceable>true-or-false</replaceable> &gt;</type>
        </inherit>
        <description>
          <para>
            A metafunction that returns <computeroutput>mpl::true_</computeroutput> if the type
            <computeroutput>T</computeroutput> is the type of a Proto domain;
            <computeroutput>mpl::false_</computeroutput> otherwise. If <computeroutput>T</computeroutput>
            inherits from <computeroutput><classname alt="proto::domain">proto::domain&lt;&gt;</classname></computeroutput>,
            <computeroutput>is_domain&lt;T&gt;</computeroutput> is <computeroutput>mpl::true_</computeroutput>.
          </para>
        </description>
      </struct>

      <!-- proto::domain_of -->
      <struct name="domain_of">
        <template>
          <template-type-parameter name="T"/>
        </template>
        <description>
          <para>
            A metafunction that returns the domain of a given type. If <computeroutput>T</computeroutput> is a Proto
            expression type, it returns that expression's associated domain. If not, it returns
            <computeroutput><classname>proto::default_domain</classname></computeroutput>.
          </para>
        </description>
        <typedef name="type">
          <type><replaceable>domain-of-T</replaceable></type>
        </typedef>
      </struct>

    </namespace>
  </namespace>
</header>
