namespace boost { namespace proto { namespace functional
{
    /// \brief A PolymorphicFunctionObject type that invokes the
    /// \c fusion::pop_back() algorithm on its argument.
    ///
    /// A PolymorphicFunctionObject type that invokes the
    /// \c fusion::pop_back() algorithm on its argument.
    struct pop_back
    {
        BOOST_PROTO_CALLABLE()

        template<typename Sig>
        struct result;

        template<typename This, typename Seq>
        struct result<This(Seq)>
          : result<This(Seq const &)>
        {};

        template<typename This, typename Seq>
        struct result<This(Seq &)>
          : fusion::result_of::pop_back<Seq>
        {};

        template<typename Seq>
        typename fusion::result_of::pop_back<Seq>::type
        operator ()(Seq &seq) const
        {
            // Work around a const-correctness issue in Fusion
            typedef typename fusion::result_of::pop_back<Seq>::type result_type;
            return result_type(fusion::begin(seq), fusion::prior(fusion::end(seq)));
        }

        template<typename Seq>
        typename fusion::result_of::pop_back<Seq const>::type
        operator ()(Seq const &seq) const
        {
            return fusion::pop_back(seq);
        }
    };
}}}

#endif
