#ifndef BOOST_PP_IS_ITERATING
    ///////////////////////////////////////////////////////////////////////////////
    /// \file expr.hpp
    /// Contains definition of expr\<\> class template.
    //
    //  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_EXPR_HPP_EAN_04_01_2005
    #define BOOST_PROTO_EXPR_HPP_EAN_04_01_2005

    #include <boost/proto/detail/prefix.hpp>
    #include <boost/preprocessor/cat.hpp>
    #include <boost/preprocessor/arithmetic/dec.hpp>
    #include <boost/preprocessor/selection/max.hpp>
    #include <boost/preprocessor/iteration/iterate.hpp>
    #include <boost/preprocessor/repetition/repeat.hpp>
    #include <boost/preprocessor/repetition/repeat_from_to.hpp>
    #include <boost/preprocessor/repetition/enum_trailing.hpp>
    #include <boost/preprocessor/repetition/enum_params.hpp>
    #include <boost/preprocessor/repetition/enum_binary_params.hpp>
    #include <boost/preprocessor/repetition/enum_trailing_params.hpp>
    #include <boost/preprocessor/repetition/enum_trailing_binary_params.hpp>
    #include <boost/utility/addressof.hpp>
    #include <boost/proto/proto_fwd.hpp>
    #include <boost/proto/args.hpp>
    #include <boost/proto/traits.hpp>
    #include <boost/proto/detail/suffix.hpp>

    #if defined(_MSC_VER) && (_MSC_VER >= 1020)
    # pragma warning(push)
    # pragma warning(disable : 4510) // default constructor could not be generated
    # pragma warning(disable : 4512) // assignment operator could not be generated
    # pragma warning(disable : 4610) // user defined constructor required
    #endif

    namespace boost { namespace proto
    {

        namespace detail
        {
        /// INTERNAL ONLY
        ///
        #define BOOST_PROTO_CHILD(Z, N, DATA)                                                       \
            typedef typename Args::BOOST_PP_CAT(child, N) BOOST_PP_CAT(proto_child, N);             \
            BOOST_PP_CAT(proto_child, N) BOOST_PP_CAT(child, N);                                    \
            /**< INTERNAL ONLY */

        /// INTERNAL ONLY
        ///
        #define BOOST_PROTO_VOID(Z, N, DATA)                                                        \
            typedef void BOOST_PP_CAT(proto_child, N);                                              \
            /**< INTERNAL ONLY */

            struct not_a_valid_type
            {
            private:
                not_a_valid_type()
                {}
            };
            
            template<typename Tag, typename Arg>
            struct address_of_hack
            {
                typedef not_a_valid_type type;
            };

            template<typename Expr>
            struct address_of_hack<proto::tag::address_of, Expr &>
            {
                typedef Expr *type;
            };

            template<typename X, std::size_t N, typename Y>
            void checked_copy(X (&x)[N], Y (&y)[N])
            {
                for(std::size_t i = 0; i < N; ++i)
                {
                    y[i] = x[i];
                }
            }

            template<typename T, std::size_t N>
            struct if_is_array
            {};

            template<typename T, std::size_t N>
            struct if_is_array<T[N], N>
            {
                typedef int type;
            };

        }

        namespace result_of
        {
            /// \brief A helper metafunction for computing the
            /// return type of \c proto::expr\<\>::operator().
            template<typename Sig, typename This, typename Domain>
            struct funop;

        #define BOOST_PP_ITERATION_PARAMS_1 (3, (0, BOOST_PP_DEC(BOOST_PROTO_MAX_FUNCTION_CALL_ARITY), <boost/proto/detail/funop.hpp>))
        #include BOOST_PP_ITERATE()
        }

        // TODO consider adding a basic_expr<> that doesn't have operator=,
        // operator[] or operator() for use by BOOST_PROTO_BASIC_EXTENDS().
        // Those member functions are unused in that case, and only slow
        // down instantiations. basic_expr::proto_base_expr can still be
        // expr<> because uses of proto_base_expr in proto::matches<> shouldn't
        // case the expr<> type to be instantiated. (<-- Check that assumtion!)
        // OR, should expr<>::proto_base_expr be a typedef for basic_expr<>?

        BOOST_PROTO_BEGIN_ADL_NAMESPACE(exprns_)
        #define BOOST_PP_ITERATION_PARAMS_1 (3, (0, BOOST_PROTO_MAX_ARITY, <boost/proto/expr.hpp>))
        #include BOOST_PP_ITERATE()
        BOOST_PROTO_END_ADL_NAMESPACE(exprns_)

        #undef BOOST_PROTO_CHILD
        #undef BOOST_PROTO_VOID

        /// \brief Lets you inherit the interface of an expression
        /// while hiding from Proto the fact that the type is a Proto
        /// expression.
        template<typename Expr>
        struct unexpr
          : Expr
        {
            BOOST_PROTO_UNEXPR()

            explicit unexpr(Expr const &expr)
              : Expr(expr)
            {}
            
            using Expr::operator =;
        };

    }}

    #if defined(_MSC_VER) && (_MSC_VER >= 1020)
    # pragma warning(pop)
    #endif

    #endif // BOOST_PROTO_EXPR_HPP_EAN_04_01_2005

// For gcc 4.4 compatability, we must include the
// BOOST_PP_ITERATION_DEPTH test inside an #else clause.
#else // BOOST_PP_IS_ITERATING
#if BOOST_PP_ITERATION_DEPTH() == 1

    #define ARG_COUNT BOOST_PP_MAX(1, BOOST_PP_ITERATION())
    #define IS_TERMINAL 0 == BOOST_PP_ITERATION()

        /// \brief Representation of a node in an expression tree.
        ///
        /// \c proto::expr\<\> is a node in an expression template tree. It
        /// is a container for its child sub-trees. It also serves as
        /// the terminal nodes of the tree.
        ///
        /// \c Tag is type that represents the operation encoded by
        ///             this expression. It is typically one of the structs
        ///             in the \c boost::proto::tag namespace, but it doesn't
        ///             have to be.
        ///
        /// \c Args is a type list representing the type of the children
        ///             of this expression. It is an instantiation of one
        ///             of \c proto::list1\<\>, \c proto::list2\<\>, etc. The
        ///             child types must all themselves be either \c expr\<\>
        ///             or <tt>proto::expr\<\>&</tt>. If \c Args is an
        ///             instantiation of \c proto::term\<\> then this
        ///             \c expr\<\> type represents a terminal expression;
        ///             the parameter to the \c proto::term\<\> template
        ///             represents the terminal's value type.
        ///
        /// \c Arity is an integral constant representing the number of child
        ///             nodes this node contains. If \c Arity is 0, then this
        ///             node is a terminal.
        ///
        /// \c proto::expr\<\> is a valid Fusion random-access sequence, where
        /// the elements of the sequence are the child expressions.
        template<typename Tag, typename Args>
        struct expr<Tag, Args, BOOST_PP_ITERATION() >
        {
            typedef Tag proto_tag;
            BOOST_STATIC_CONSTANT(long, proto_arity_c = BOOST_PP_ITERATION());
            typedef mpl::long_<BOOST_PP_ITERATION() > proto_arity;
            typedef expr proto_base_expr;
            typedef Args proto_args;
            typedef default_domain proto_domain;
            BOOST_PROTO_FUSION_DEFINE_TAG(proto::tag::proto_expr)
            typedef expr proto_derived_expr;
            typedef void proto_is_expr_; /**< INTERNAL ONLY */

            BOOST_PP_REPEAT(ARG_COUNT, BOOST_PROTO_CHILD, ~)
            BOOST_PP_REPEAT_FROM_TO(ARG_COUNT, BOOST_PROTO_MAX_ARITY, BOOST_PROTO_VOID, ~)

            /// \return *this
            ///
            expr const &proto_base() const
            {
                return *this;
            }

            /// \overload
            ///
            expr &proto_base()
            {
                return *this;
            }

            /// \return A new \c expr\<\> object initialized with the specified
            /// arguments.
            ///
            template<BOOST_PP_ENUM_PARAMS(ARG_COUNT, typename A)>
            static expr const make(BOOST_PP_ENUM_BINARY_PARAMS(ARG_COUNT, A, const &a))
            {
                expr that = {BOOST_PP_ENUM_PARAMS(ARG_COUNT, a)};
                return that;
            }

        #if IS_TERMINAL
            /// \overload
            ///
            template<typename A0>
            static expr const make(A0 &a0)
            {
                expr that = {a0};
                return that;
            }

            /// \overload
            ///
            template<typename A0, std::size_t N>
            static expr const make(A0 (&a0)[N], typename detail::if_is_array<proto_child0, N>::type = 0)
            {
                expr that;
                detail::checked_copy(a0, that.child0);
                return that;
            }

            /// \overload
            ///
            template<typename A0, std::size_t N>
            static expr const make(A0 const (&a0)[N], typename detail::if_is_array<proto_child0, N>::type = 0)
            {
                expr that;
                detail::checked_copy(a0, that.child0);
                return that;
            }
        #endif

        #if 1 == BOOST_PP_ITERATION()
            /// If \c Tag is \c boost::proto::tag::address_of and \c proto_child0 is
            /// <tt>T&</tt>, then \c address_of_hack_type_ is <tt>T*</tt>.
            /// Otherwise, it is some undefined type.
            typedef typename detail::address_of_hack<Tag, proto_child0>::type address_of_hack_type_;

            /// \return The address of <tt>this->child0</tt> if \c Tag is
            /// \c boost::proto::tag::address_of. Otherwise, this function will
            /// fail to compile.
            ///
            /// \attention Proto overloads <tt>operator&</tt>, which means that
            /// proto-ified objects cannot have their addresses taken, unless we use
            /// the following hack to make \c &x implicitly convertible to \c X*.
            operator address_of_hack_type_() const
            {
                return boost::addressof(this->child0);
            }
        #else
            /// INTERNAL ONLY
            ///
            typedef detail::not_a_valid_type address_of_hack_type_;
        #endif

            /// Assignment
            ///
            /// \param a The rhs.
            /// \return A new \c expr\<\> node representing an assignment of \c a to \c *this.
            template<typename A>
            proto::expr<
                proto::tag::assign
              , list2<expr const &, typename result_of::as_child<A>::type>
            > const
            operator =(A &a) const
            {
                proto::expr<
                    proto::tag::assign
                  , list2<expr const &, typename result_of::as_child<A>::type>
                > that = {*this, proto::as_child(a)};
                return that;
            }

            /// \overload
            ///
            template<typename A>
            proto::expr<
                proto::tag::assign
              , list2<expr const &, typename result_of::as_child<A const>::type>
            > const
            operator =(A const &a) const
            {
                proto::expr<
                    proto::tag::assign
                  , list2<expr const &, typename result_of::as_child<A const>::type>
                > that = {*this, proto::as_child(a)};
                return that;
            }

        #if IS_TERMINAL
            /// \overload
            ///
            template<typename A>
            proto::expr<
                proto::tag::assign
              , list2<expr &, typename result_of::as_child<A>::type>
            > const
            operator =(A &a)
            {
                proto::expr<
                    proto::tag::assign
                  , list2<expr &, typename result_of::as_child<A>::type>
                > that = {*this, proto::as_child(a)};
                return that;
            }

            /// \overload
            ///
            template<typename A>
            proto::expr<
                proto::tag::assign
              , list2<expr &, typename result_of::as_child<A const>::type>
            > const
            operator =(A const &a)
            {
                proto::expr<
                    proto::tag::assign
                  , list2<expr &, typename result_of::as_child<A const>::type>
                > that = {*this, proto::as_child(a)};
                return that;
            }
        #endif

            /// Subscript
            ///
            /// \param a The rhs.
            /// \return A new \c expr\<\> node representing \c *this subscripted with \c a.
            template<typename A>
            proto::expr<
                proto::tag::subscript
              , list2<expr const &, typename result_of::as_child<A>::type>
            > const
            operator [](A &a) const
            {
                proto::expr<
                    proto::tag::subscript
                  , list2<expr const &, typename result_of::as_child<A>::type>
                > that = {*this, proto::as_child(a)};
                return that;
            }

            /// \overload
            ///
            template<typename A>
            proto::expr<
                proto::tag::subscript
              , list2<expr const &, typename result_of::as_child<A const>::type> > const
            operator [](A const &a) const
            {
                proto::expr<
                    proto::tag::subscript
                  , list2<expr const &, typename result_of::as_child<A const>::type>
                > that = {*this, proto::as_child(a)};
                return that;
            }

        #if IS_TERMINAL
            /// \overload
            ///
            template<typename A>
            proto::expr<
                proto::tag::subscript
              , list2<expr &, typename result_of::as_child<A>::type>
            > const
            operator [](A &a)
            {
                proto::expr<
                    proto::tag::subscript
                  , list2<expr &, typename result_of::as_child<A>::type>
                > that = {*this, proto::as_child(a)};
                return that;
            }

            /// \overload
            ///
            template<typename A>
            proto::expr<
                proto::tag::subscript
              , list2<expr &, typename result_of::as_child<A const>::type>
            > const
            operator [](A const &a)
            {
                proto::expr<
                    proto::tag::subscript
                  , list2<expr &, typename result_of::as_child<A const>::type>
                > that = {*this, proto::as_child(a)};
                return that;
            }
        #endif

            /// Encodes the return type of \c expr\<\>::operator(), for use with \c boost::result_of\<\>
            ///
            template<typename Sig>
            struct result
            {
                typedef typename result_of::funop<Sig, expr, default_domain>::type const type;
            };

            /// Function call
            ///
            /// \return A new \c expr\<\> node representing the function invocation of \c (*this)().
            proto::expr<proto::tag::function, list1<expr const &> > const
            operator ()() const
            {
                proto::expr<proto::tag::function, list1<expr const &> > that = {*this};
                return that;
            }

        #if IS_TERMINAL
            /// \overload
            ///
            proto::expr<proto::tag::function, list1<expr &> > const
            operator ()()
            {
                proto::expr<proto::tag::function, list1<expr &> > that = {*this};
                return that;
            }
        #endif

    #define BOOST_PP_ITERATION_PARAMS_2 (3, (1, BOOST_PP_DEC(BOOST_PROTO_MAX_FUNCTION_CALL_ARITY), <boost/proto/expr.hpp>))
    #include BOOST_PP_ITERATE()
        };

    #undef ARG_COUNT
    #undef IS_TERMINAL

#elif BOOST_PP_ITERATION_DEPTH() == 2

    #define N BOOST_PP_ITERATION()

        /// \overload
        ///
        template<BOOST_PP_ENUM_PARAMS(N, typename A)>
        typename result_of::BOOST_PP_CAT(funop, N)<
            expr const
          , default_domain BOOST_PP_ENUM_TRAILING_PARAMS(N, const A)
        >::type const
        operator ()(BOOST_PP_ENUM_BINARY_PARAMS(N, A, const &a)) const
        {
            return result_of::BOOST_PP_CAT(funop, N)<
                expr const
              , default_domain BOOST_PP_ENUM_TRAILING_PARAMS(N, const A)
            >::call(*this BOOST_PP_ENUM_TRAILING_PARAMS(N, a));
        }

        #if IS_TERMINAL
        /// \overload
        ///
        template<BOOST_PP_ENUM_PARAMS(N, typename A)>
        typename result_of::BOOST_PP_CAT(funop, N)<
            expr
          , default_domain BOOST_PP_ENUM_TRAILING_PARAMS(N, const A)
        >::type const
        operator ()(BOOST_PP_ENUM_BINARY_PARAMS(N, A, const &a))
        {
            return result_of::BOOST_PP_CAT(funop, N)<
                expr
              , default_domain BOOST_PP_ENUM_TRAILING_PARAMS(N, const A)
            >::call(*this BOOST_PP_ENUM_TRAILING_PARAMS(N, a));
        }
        #endif

    #undef N

#endif // BOOST_PP_ITERATION_DEPTH()
#endif