text: #if !defined(BOOST_PROTO_DONT_USE_PREPROCESSED_FILES)
  
      #include <boost/proto/transform/detail/preprocessed/fold_impl.hpp>
  
  #elif !defined(BOOST_PP_IS_ITERATING)
  
      #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>(e)                                                                \
                , BOOST_PP_CAT(s, N)                                                                  \
                , d                                                                                   \
              );                                                                                      \
          /**/
  
      #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))>(e)                              \
                , BOOST_PP_CAT(s, BOOST_PP_SUB(DATA, N))                                              \
                , d                                                                                   \
              );                                                                                      \
          /**/
  
      #if defined(__WAVE__) && defined(BOOST_PROTO_CREATE_PREPROCESSED_FILES)
          #pragma wave option(preserve: 2, line: 0, output: "preprocessed/fold_impl.hpp")
      #endif
  
      ///////////////////////////////////////////////////////////////////////////////
      /// \file fold_impl.hpp
      /// Contains definition of fold_impl<> and reverse_fold_impl<> templates.
      //
      //  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)
  
      #if defined(__WAVE__) && defined(BOOST_PROTO_CREATE_PREPROCESSED_FILES)
          #pragma wave option(preserve: 1)
      #endif
  
      #define BOOST_PP_ITERATION_PARAMS_1                                                             \
          (3, (1, BOOST_PROTO_MAX_ARITY, <boost/proto/transform/detail/fold_impl.hpp>))
      #include BOOST_PP_ITERATE()
  
      #if defined(__WAVE__) && defined(BOOST_PROTO_CREATE_PREPROCESSED_FILES)
          #pragma wave option(output: null)
      #endif
  
      #undef BOOST_PROTO_REVERSE_FOLD_STATE
      #undef BOOST_PROTO_REVERSE_FOLD_STATE_TYPE
      #undef BOOST_PROTO_FOLD_STATE
      #undef BOOST_PROTO_FOLD_STATE_TYPE
      #undef BOOST_PROTO_CHILD_N_TYPE
  
  #else
  
      #define N BOOST_PP_ITERATION()
  
      template<typename State0, typename Fun, typename Expr, typename State, typename Data>
      struct fold_impl<State0, Fun, Expr, State, Data, N>
        : transform_impl<Expr, State, Data>
      {
          typedef typename when<_, State0>::template impl<Expr, State, Data>::result_type state0;
          BOOST_PP_REPEAT(N, BOOST_PROTO_FOLD_STATE_TYPE, N)
          typedef BOOST_PP_CAT(state, N) result_type;
  
          result_type operator ()(
              typename fold_impl::expr_param e
            , typename fold_impl::state_param s
            , typename fold_impl::data_param d
          ) const
          {
              state0 s0 =
                  typename when<_, State0>::template impl<Expr, State, Data>()(e, s, d);
              BOOST_PP_REPEAT(N, BOOST_PROTO_FOLD_STATE, N)
              return BOOST_PP_CAT(s, N);
          }
      };
  
      template<typename State0, typename Fun, typename Expr, typename State, typename Data>
      struct reverse_fold_impl<State0, Fun, Expr, State, Data, N>
        : transform_impl<Expr, State, Data>
      {
          typedef typename when<_, State0>::template impl<Expr, State, Data>::result_type BOOST_PP_CAT(state, N);
          BOOST_PP_REPEAT(N, BOOST_PROTO_REVERSE_FOLD_STATE_TYPE, N)
          typedef state0 result_type;
  
          result_type operator ()(
              typename reverse_fold_impl::expr_param e
            , typename reverse_fold_impl::state_param s
            , typename reverse_fold_impl::data_param d
          ) const
          {
              BOOST_PP_CAT(state, N) BOOST_PP_CAT(s, N) =
                  typename when<_, State0>::template impl<Expr, State, Data>()(e, s, d);
              BOOST_PP_REPEAT(N, BOOST_PROTO_REVERSE_FOLD_STATE, N)
              return s0;
          }
      };
  
      #undef N
  
  #endif
  