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///////////////////////////////////////////////////////////////////////////////
/// \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/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>
#include <boost/fusion/include/fold.hpp>
#include <boost/fusion/include/reverse_fold.hpp>
#include <boost/proto/proto_fwd.hpp>
#include <boost/proto/traits.hpp>
#include <boost/proto/transform/impl.hpp>
#include <boost/proto/transform/when.hpp>
namespace boost { namespace proto
{
namespace detail
{
template<typename Transform, typename Data>
struct as_callable
{
as_callable(Data d)
: d_(d)
{}
template<typename Sig>
struct result;
template<typename This, typename State, typename Expr>
struct result<This(State, Expr)>
{
typedef
typename when<_, Transform>::template impl<Expr, State, Data>::result_type
type;
};
template<typename State, typename Expr>
typename when<_, Transform>::template impl<Expr &, State const &, Data>::result_type
operator ()(State const &s, Expr &e) const
{
return typename when<_, Transform>::template impl<Expr &, State const &, Data>()(e, s, this->d_);
}
private:
Data d_;
};
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
{};
#include <boost/proto/transform/detail/fold_impl.hpp>
} // namespace detail
/// \brief A PrimitiveTransform that invokes the <tt>fusion::fold\<\></tt>
/// algorithm to accumulate
template<typename Sequence, typename State0, typename Fun>
struct fold : transform<fold<Sequence, State0, Fun> >
{
template<typename Expr, typename State, typename Data>
struct impl : transform_impl<Expr, State, Data>
{
/// \brief A Fusion sequence.
typedef
typename remove_reference<
typename when<_, Sequence>::template impl<Expr, State, Data>::result_type
>::type
sequence;
/// \brief An initial state for the fold.
typedef
typename remove_reference<
typename when<_, State0>::template impl<Expr, State, Data>::result_type
>::type
state0;
/// \brief <tt>fun(d)(e,s) == when\<_,Fun\>()(e,s,d)</tt>
typedef
detail::as_callable<Fun, Data>
fun;
typedef
typename fusion::result_of::fold<
sequence
, state0
, fun
>::type
result_type;
/// Let \c seq be <tt>when\<_, Sequence\>()(e, s, d)</tt>, let
/// \c state0 be <tt>when\<_, State0\>()(e, s, d)</tt>, and
/// let \c fun(d) be an object such that <tt>fun(d)(e, s)</tt>
/// is equivalent to <tt>when\<_, Fun\>()(e, s, d)</tt>. Then, this
/// function returns <tt>fusion::fold(seq, state0, fun(d))</tt>.
///
/// \param e The current expression
/// \param s The current state
/// \param d An arbitrary data
result_type operator ()(
typename impl::expr_param e
, typename impl::state_param s
, typename impl::data_param d
) const
{
typename when<_, Sequence>::template impl<Expr, State, Data> seq;
detail::as_callable<Fun, Data> f(d);
return fusion::fold(
seq(e, s, d)
, typename when<_, State0>::template impl<Expr, State, Data>()(e, s, d)
, f
);
}
};
};
/// \brief A PrimitiveTransform that is the same as the
/// <tt>fold\<\></tt> transform, except that it folds
/// back-to-front instead of front-to-back.
template<typename Sequence, typename State0, typename Fun>
struct reverse_fold : transform<reverse_fold<Sequence, State0, Fun> >
{
template<typename Expr, typename State, typename Data>
struct impl : transform_impl<Expr, State, Data>
{
/// \brief A Fusion sequence.
typedef
typename remove_reference<
typename when<_, Sequence>::template impl<Expr, State, Data>::result_type
>::type
sequence;
/// \brief An initial state for the fold.
typedef
typename remove_reference<
typename when<_, State0>::template impl<Expr, State, Data>::result_type
>::type
state0;
/// \brief <tt>fun(d)(e,s) == when\<_,Fun\>()(e,s,d)</tt>
typedef
detail::as_callable<Fun, Data>
fun;
typedef
typename fusion::result_of::reverse_fold<
sequence
, state0
, fun
>::type
result_type;
/// Let \c seq be <tt>when\<_, Sequence\>()(e, s, d)</tt>, let
/// \c state0 be <tt>when\<_, State0\>()(e, s, d)</tt>, and
/// let \c fun(d) be an object such that <tt>fun(d)(e, s)</tt>
/// is equivalent to <tt>when\<_, Fun\>()(e, s, d)</tt>. Then, this
/// function returns <tt>fusion::fold(seq, state0, fun(d))</tt>.
///
/// \param e The current expression
/// \param s The current state
/// \param d An arbitrary data
result_type operator ()(
typename impl::expr_param e
, typename impl::state_param s
, typename impl::data_param d
) const
{
typename when<_, Sequence>::template impl<Expr, State, Data> seq;
detail::as_callable<Fun, Data> f(d);
return fusion::reverse_fold(
seq(e, s, d)
, typename when<_, State0>::template impl<Expr, State, Data>()(e, s, d)
, f
);
}
};
};
// This specialization is only for improved compile-time performance
// in the commom case when the Sequence transform is \c proto::_.
//
/// INTERNAL ONLY
///
template<typename State0, typename Fun>
struct fold<_, State0, Fun> : transform<fold<_, State0, Fun> >
{
template<typename Expr, typename State, typename Data>
struct impl
: detail::fold_impl<State0, Fun, Expr, State, Data>
{};
};
// This specialization is only for improved compile-time performance
// in the commom case when the Sequence transform is \c proto::_.
//
/// INTERNAL ONLY
///
template<typename State0, typename Fun>
struct reverse_fold<_, State0, Fun> : transform<reverse_fold<_, State0, Fun> >
{
template<typename Expr, typename State, typename Data>
struct impl
: detail::reverse_fold_impl<State0, Fun, Expr, State, Data>
{};
};
/// INTERNAL ONLY
///
template<typename Sequence, typename State, typename Fun>
struct is_callable<fold<Sequence, State, Fun> >
: mpl::true_
{};
/// INTERNAL ONLY
///
template<typename Sequence, typename State, typename Fun>
struct is_callable<reverse_fold<Sequence, State, Fun> >
: mpl::true_
{};
}}
#endif
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