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/*!
@file
Defines `boost::hana::monadic_fold_right`.
@copyright Louis Dionne 2013-2016
Distributed under the Boost Software License, Version 1.0.
(See accompanying file LICENSE.md or copy at http://boost.org/LICENSE_1_0.txt)
*/
#ifndef BOOST_HANA_MONADIC_FOLD_RIGHT_HPP
#define BOOST_HANA_MONADIC_FOLD_RIGHT_HPP
#include <boost/hana/fwd/monadic_fold_right.hpp>
#include <boost/hana/chain.hpp>
#include <boost/hana/concept/foldable.hpp>
#include <boost/hana/concept/monad.hpp>
#include <boost/hana/config.hpp>
#include <boost/hana/core/dispatch.hpp>
#include <boost/hana/detail/decay.hpp>
#include <boost/hana/fold_left.hpp>
#include <boost/hana/functional/curry.hpp>
#include <boost/hana/functional/partial.hpp>
#include <boost/hana/lift.hpp>
#include <type_traits>
BOOST_HANA_NAMESPACE_BEGIN
template <typename M>
struct monadic_fold_right_t {
#ifndef BOOST_HANA_CONFIG_DISABLE_CONCEPT_CHECKS
static_assert(hana::Monad<M>::value,
"hana::monadic_fold_right<M> requires 'M' to be a Monad");
#endif
template <typename Xs, typename State, typename F>
constexpr decltype(auto) operator()(Xs&& xs, State&& state, F&& f) const {
using S = typename hana::tag_of<Xs>::type;
using MonadicFoldRight = BOOST_HANA_DISPATCH_IF(monadic_fold_right_impl<S>,
hana::Foldable<S>::value
);
#ifndef BOOST_HANA_CONFIG_DISABLE_CONCEPT_CHECKS
static_assert(hana::Foldable<S>::value,
"hana::monadic_fold_right<M>(xs, state, f) requires 'xs' to be Foldable");
#endif
return MonadicFoldRight::template apply<M>(static_cast<Xs&&>(xs),
static_cast<State&&>(state),
static_cast<F&&>(f));
}
template <typename Xs, typename F>
constexpr decltype(auto) operator()(Xs&& xs, F&& f) const {
using S = typename hana::tag_of<Xs>::type;
using MonadicFoldRight = BOOST_HANA_DISPATCH_IF(monadic_fold_right_impl<S>,
hana::Foldable<S>::value
);
#ifndef BOOST_HANA_CONFIG_DISABLE_CONCEPT_CHECKS
static_assert(hana::Foldable<S>::value,
"hana::monadic_fold_right<M>(xs, f) requires 'xs' to be Foldable");
#endif
return MonadicFoldRight::template apply<M>(static_cast<Xs&&>(xs),
static_cast<F&&>(f));
}
};
namespace detail {
struct foldrM_helper {
template <typename F, typename K, typename X, typename Z>
constexpr decltype(auto) operator()(F&& f, K&& k, X&& x, Z&& z) const {
return hana::chain(
static_cast<F&&>(f)(
static_cast<X&&>(x),
static_cast<Z&&>(z)
),
static_cast<K&&>(k)
);
}
};
template <typename End, typename M, typename F>
struct monadic_foldr1_helper {
F f;
template <typename X, typename Y>
constexpr decltype(auto) operator()(X&& x, Y&& y) const
{ return f(static_cast<X&&>(x), static_cast<Y&&>(y)); }
template <typename X>
constexpr decltype(auto) operator()(X&& x, End) const
{ return hana::lift<M>(static_cast<X&&>(x)); }
};
}
template <typename T, bool condition>
struct monadic_fold_right_impl<T, when<condition>> : default_ {
// with state
template <typename M, typename Xs, typename S, typename F>
static constexpr decltype(auto) apply(Xs&& xs, S&& s, F&& f) {
return hana::fold_left(
static_cast<Xs&&>(xs),
hana::lift<M>,
hana::curry<3>(hana::partial(
detail::foldrM_helper{}, static_cast<F&&>(f)
))
)(static_cast<S&&>(s));
}
// without state
template <typename M, typename Xs, typename F>
static constexpr decltype(auto) apply(Xs&& xs, F&& f) {
struct end { };
using G = detail::monadic_foldr1_helper<end, M, typename detail::decay<F>::type>;
decltype(auto) result = hana::monadic_fold_right<M>(
static_cast<Xs&&>(xs),
end{},
G{static_cast<F&&>(f)}
);
static_assert(!std::is_same<
std::remove_reference_t<decltype(result)>,
decltype(hana::lift<M>(end{}))
>{},
"hana::monadic_fold_right<M>(xs, f) requires 'xs' to be non-empty");
return result;
}
};
BOOST_HANA_NAMESPACE_END
#endif // !BOOST_HANA_MONADIC_FOLD_RIGHT_HPP
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