meta_grammar.hpp

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//  Copyright (c) 2001-2008 Hartmut Kaiser
// 
//  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)

#if !defined(BOOST_SPIRIT_KARMA_META_GRAMMAR_MAR_04_2007_0907AM)
#define BOOST_SPIRIT_KARMA_META_GRAMMAR_MAR_04_2007_0907AM

#if defined(_MSC_VER) && (_MSC_VER >= 1020)
#pragma once      // MS compatible compilers support #pragma once
#endif

#include <boost/spirit/home/karma/domain.hpp>
#include <boost/spirit/home/support/meta_grammar.hpp>
#include <boost/utility/enable_if.hpp>

namespace boost { namespace spirit { namespace karma
{
    ///////////////////////////////////////////////////////////////////////////
    // forwards
    /////////////////////////////////////////////////////////////////////////// 
    struct action;

    struct main_meta_grammar;

    template <typename Expr, typename Enable>
    struct is_valid_expr;

    template <typename Expr, typename Enable>
    struct expr_transform;

    ///////////////////////////////////////////////////////////////////////////
    // action meta-grammar
    ///////////////////////////////////////////////////////////////////////////
    struct action_meta_grammar : 
        meta_grammar::binary_rule<
            karma::domain, proto::tag::subscript, action,
            main_meta_grammar, proto::when<proto::_, proto::_arg>
        >
    {
    };

    ///////////////////////////////////////////////////////////////////////////
    //  These specializations non-intrusively hooks into the Karma meta-grammar.
    //  (see karma/meta_grammar.hpp)
    ///////////////////////////////////////////////////////////////////////////
    template <typename Expr>
    struct is_valid_expr<
            Expr,
            typename enable_if<
                proto::matches<Expr, action_meta_grammar> 
            >::type
        >
      : mpl::true_
    {
    };

    template <typename Expr>
    struct expr_transform<
            Expr,
            typename enable_if<
                proto::matches<Expr, action_meta_grammar> 
            >::type
        >
      : mpl::identity<action_meta_grammar>
    {
    };
}}}

#endif