/*=============================================================================

    Copyright (c) 2001-2006 Joel de Guzman



    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(FUSION_EMPTY_09162005_0335)

#define FUSION_EMPTY_09162005_0335



#include <boost/fusion/sequence/intrinsic/size.hpp>

#include <boost/mpl/bool.hpp>

#include <boost/fusion/support/tag_of.hpp>



namespace boost { namespace fusion

{

    // Special tags:

    struct sequence_facade_tag;

    struct mpl_sequence_tag; // mpl sequence tag



    namespace extension

    {

        template <typename Tag>

        struct empty_impl

        {

            template <typename Sequence>

            struct apply 

                : mpl::bool_<(result_of::size<Sequence>::value == 0)>

            {};

        };



        template <>

        struct empty_impl<sequence_facade_tag>

        {

            template <typename Sequence>

            struct apply : Sequence::template empty<Sequence> {};

        };



        template <>

        struct empty_impl<mpl_sequence_tag>;

    }



    namespace result_of

    {

        template <typename Sequence>

        struct empty 

            : extension::empty_impl<typename detail::tag_of<Sequence>::type>::

                template apply<Sequence>

        {};

    }



    template <typename Sequence>

    inline typename result_of::empty<Sequence>::type

    empty(Sequence const&)

    {

        typedef typename result_of::empty<Sequence>::type result;

        return result();

    }

}}



#endif

