fold.hpp

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#ifndef BOOST_PP_IS_ITERATING
    ///////////////////////////////////////////////////////////////////////////////
    /// \file fold.hpp
    /// Contains definition of the fold<> and reverse_fold<> transforms.
    //
    //  Copyright 2008 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)

    #ifndef BOOST_PROTO_TRANSFORM_FOLD_HPP_EAN_11_04_2007
    #define BOOST_PROTO_TRANSFORM_FOLD_HPP_EAN_11_04_2007

    #include <boost/proto/detail/prefix.hpp>
    #include <boost/version.hpp>
    #include <boost/preprocessor/cat.hpp>
    #include <boost/preprocessor/iteration/iterate.hpp>
    #include <boost/preprocessor/arithmetic/inc.hpp>
    #include <boost/preprocessor/arithmetic/sub.hpp>
    #include <boost/preprocessor/repetition/repeat.hpp>
    #if BOOST_VERSION >= 103500
    #include <boost/fusion/include/fold.hpp>
    #else
    #include <boost/spirit/fusion/algorithm/fold.hpp>
    #endif
    #include <boost/proto/proto_fwd.hpp>
    #include <boost/proto/fusion.hpp>
    #include <boost/proto/traits.hpp>
    #include <boost/proto/transform/call.hpp>
    #include <boost/proto/transform/impl.hpp>
    #include <boost/proto/detail/suffix.hpp>

    namespace boost { namespace proto
    {
        namespace detail
        {
            template<typename Transform, typename Data>
            struct as_callable
            {
                as_callable(Data v)
                  : v_(v)
                {}

                template<typename Sig>
                struct result;

                template<typename This, typename Expr, typename State>
                struct result<This(Expr, State)>
                {
                    typedef
                        typename when<_, Transform>::template impl<Expr, State, Data>::result_type
                    type;
                };

                #if BOOST_VERSION < 103500
                template<typename Expr, typename State>
                struct apply
                  : result<void(Expr, State)>
                {};
                #endif

                template<typename Expr, typename State>
                typename when<_, Transform>::template impl<Expr &, State const &, Data>::result_type
                operator ()(Expr &expr, State const &state) const
                {
                    return typename when<_, Transform>::template impl<Expr &, State const &, Data>()(expr, state, this->v_);
                }

            private:
                Data v_;
            };

            #if BOOST_VERSION < 103500
            template<typename Sequence, typename Void = void>
            struct as_fusion_sequence_type
            {
                typedef Sequence const type;
            };

            template<typename Sequence>
            Sequence const &as_fusion_sequence(Sequence const &sequence, ...)
            {
                return sequence;
            }

            template<typename Sequence>
            struct as_fusion_sequence_type<Sequence, typename Sequence::proto_is_expr_>
            {
                typedef typename Sequence::proto_base_expr const type;
            };

            template<typename Sequence>
            typename Sequence::proto_base_expr const &as_fusion_sequence(Sequence const &sequence, int)
            {
                return sequence.proto_base();
            }

            #define BOOST_PROTO_AS_FUSION_SEQUENCE_TYPE(X) typename detail::as_fusion_sequence_type<X>::type
            #define BOOST_PROTO_AS_FUSION_SEQUENCE(X) detail::as_fusion_sequence(X, 0)
            #else
            #define BOOST_PROTO_AS_FUSION_SEQUENCE_TYPE(X) X
            #define BOOST_PROTO_AS_FUSION_SEQUENCE(X) X
            #endif

            template<
                typename State0
              , typename Fun
              , typename Expr
              , typename State
              , typename Data
              , long Arity = arity_of<Expr>::value
            >
            struct fold_impl
            {};

            template<
                typename State0
              , typename Fun
              , typename Expr
              , typename State
              , typename Data
              , long Arity = arity_of<Expr>::value
            >
            struct reverse_fold_impl
            {};

            #define BOOST_PROTO_CHILD_N_TYPE(N)\
                BOOST_PP_CAT(proto_child, N)\
                /**/

            #define BOOST_PROTO_FOLD_STATE_TYPE(Z, N, DATA)                                     \
                typedef                                                                         \
                    typename when<_, Fun>::template impl<                                       \
                        typename result_of::child_c<Expr, N>::type                              \
                      , BOOST_PP_CAT(state, N)                                                  \
                      , Data                                                                    \
                    >::result_type                                                              \
                BOOST_PP_CAT(state, BOOST_PP_INC(N));                                           \
                /**/

            #define BOOST_PROTO_FOLD_STATE(Z, N, DATA)                                          \
                BOOST_PP_CAT(state, BOOST_PP_INC(N))                                            \
                BOOST_PP_CAT(s, BOOST_PP_INC(N))                                                \
                  = typename when<_, Fun>::template impl<                                       \
                        typename result_of::child_c<Expr, N>::type                              \
                      , BOOST_PP_CAT(state, N)                                                  \
                      , Data                                                                    \
                    >()(                                                                        \
                        proto::child_c<N>(expr)                                                 \
                      , BOOST_PP_CAT(s, N)                                                      \
                      , data                                                                    \
                    );                                                                          \
                /**/

            #define BOOST_PROTO_REVERSE_FOLD_STATE_TYPE(Z, N, DATA)                             \
                typedef                                                                         \
                    typename when<_, Fun>::template impl<                                       \
                        typename result_of::child_c<                                            \
                            Expr                                                                \
                          , BOOST_PP_SUB(DATA, BOOST_PP_INC(N))                                 \
                        >::type                                                                 \
                      , BOOST_PP_CAT(state, BOOST_PP_SUB(DATA, N))                              \
                      , Data                                                                    \
                    >::result_type                                                              \
                BOOST_PP_CAT(state, BOOST_PP_SUB(DATA, BOOST_PP_INC(N)));                       \
                /**/

            #define BOOST_PROTO_REVERSE_FOLD_STATE(Z, N, DATA)                                  \
                BOOST_PP_CAT(state, BOOST_PP_SUB(DATA, BOOST_PP_INC(N)))                        \
                BOOST_PP_CAT(s, BOOST_PP_SUB(DATA, BOOST_PP_INC(N)))                            \
                  = typename when<_, Fun>::template impl<                                       \
                        typename result_of::child_c<                                            \
                            Expr                                                                \
                          , BOOST_PP_SUB(DATA, BOOST_PP_INC(N))                                 \
                        >::type                                                                 \
                      , BOOST_PP_CAT(state, BOOST_PP_SUB(DATA, N))                              \
                      , Data                                                                    \
                    >()(                                                                        \
                        proto::child_c<BOOST_PP_SUB(DATA, BOOST_PP_INC(N))>(expr)               \
                      , BOOST_PP_CAT(s, BOOST_PP_SUB(DATA, N))                                  \
                      , data                                                                    \
                    );                                                                          \