230 lines
8.0 KiB
C++
230 lines
8.0 KiB
C++
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/*!
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@file
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Defines `boost::hana::lazy`.
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@copyright Louis Dionne 2013-2016
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Distributed under the Boost Software License, Version 1.0.
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(See accompanying file LICENSE.md or copy at http://boost.org/LICENSE_1_0.txt)
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*/
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#ifndef BOOST_HANA_LAZY_HPP
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#define BOOST_HANA_LAZY_HPP
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#include <boost/hana/fwd/lazy.hpp>
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#include <boost/hana/basic_tuple.hpp>
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#include <boost/hana/config.hpp>
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#include <boost/hana/core/make.hpp>
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#include <boost/hana/detail/decay.hpp>
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#include <boost/hana/detail/operators/adl.hpp>
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#include <boost/hana/detail/operators/monad.hpp>
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#include <boost/hana/functional/apply.hpp>
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#include <boost/hana/functional/compose.hpp>
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#include <boost/hana/functional/on.hpp>
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#include <boost/hana/fwd/ap.hpp>
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#include <boost/hana/fwd/duplicate.hpp>
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#include <boost/hana/fwd/eval.hpp>
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#include <boost/hana/fwd/extend.hpp>
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#include <boost/hana/fwd/extract.hpp>
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#include <boost/hana/fwd/flatten.hpp>
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#include <boost/hana/fwd/lift.hpp>
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#include <boost/hana/fwd/transform.hpp>
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#include <cstddef>
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#include <type_traits>
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#include <utility>
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BOOST_HANA_NAMESPACE_BEGIN
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//////////////////////////////////////////////////////////////////////////
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// lazy
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//////////////////////////////////////////////////////////////////////////
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template <typename Indices, typename F, typename ...Args>
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struct lazy_apply_t;
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namespace detail { struct lazy_secret { }; }
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template <std::size_t ...n, typename F, typename ...Args>
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struct lazy_apply_t<std::index_sequence<n...>, F, Args...>
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: detail::operators::adl<>
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{
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template <typename ...T>
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constexpr lazy_apply_t(detail::lazy_secret, T&& ...t)
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: storage_{static_cast<T&&>(t)...}
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{ }
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basic_tuple<F, Args...> storage_;
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using hana_tag = lazy_tag;
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};
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template <typename X>
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struct lazy_value_t : detail::operators::adl<> {
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template <typename Y>
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constexpr lazy_value_t(detail::lazy_secret, Y&& y)
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: storage_{static_cast<Y&&>(y)}
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{ }
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basic_tuple<X> storage_;
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using hana_tag = lazy_tag;
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// If this is called, we assume that `X` is in fact a function.
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template <typename ...Args>
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constexpr lazy_apply_t<
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std::make_index_sequence<sizeof...(Args)>,
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X, typename detail::decay<Args>::type...
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> operator()(Args&& ...args) const& {
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return {detail::lazy_secret{},
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hana::get_impl<0>(storage_), static_cast<Args&&>(args)...};
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}
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template <typename ...Args>
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constexpr lazy_apply_t<
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std::make_index_sequence<sizeof...(Args)>,
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X, typename detail::decay<Args>::type...
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> operator()(Args&& ...args) && {
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return {detail::lazy_secret{},
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static_cast<X&&>(hana::get_impl<0>(storage_)),
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static_cast<Args&&>(args)...
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};
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}
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};
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//////////////////////////////////////////////////////////////////////////
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// make<lazy_tag>
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//////////////////////////////////////////////////////////////////////////
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template <>
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struct make_impl<lazy_tag> {
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template <typename X>
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static constexpr lazy_value_t<typename detail::decay<X>::type> apply(X&& x) {
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return {detail::lazy_secret{}, static_cast<X&&>(x)};
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}
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};
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//////////////////////////////////////////////////////////////////////////
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// Operators
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//////////////////////////////////////////////////////////////////////////
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namespace detail {
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template <>
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struct monad_operators<lazy_tag> { static constexpr bool value = true; };
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}
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//////////////////////////////////////////////////////////////////////////
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// eval for lazy_tag
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//////////////////////////////////////////////////////////////////////////
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template <>
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struct eval_impl<lazy_tag> {
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// lazy_apply_t
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template <std::size_t ...n, typename F, typename ...Args>
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static constexpr decltype(auto)
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apply(lazy_apply_t<std::index_sequence<n...>, F, Args...> const& expr) {
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return hana::get_impl<0>(expr.storage_)(
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hana::get_impl<n+1>(expr.storage_)...
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);
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}
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template <std::size_t ...n, typename F, typename ...Args>
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static constexpr decltype(auto)
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apply(lazy_apply_t<std::index_sequence<n...>, F, Args...>& expr) {
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return hana::get_impl<0>(expr.storage_)(
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hana::get_impl<n+1>(expr.storage_)...
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);
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}
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template <std::size_t ...n, typename F, typename ...Args>
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static constexpr decltype(auto)
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apply(lazy_apply_t<std::index_sequence<n...>, F, Args...>&& expr) {
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return static_cast<F&&>(hana::get_impl<0>(expr.storage_))(
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static_cast<Args&&>(hana::get_impl<n+1>(expr.storage_))...
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);
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}
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// lazy_value_t
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template <typename X>
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static constexpr X const& apply(lazy_value_t<X> const& expr)
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{ return hana::get_impl<0>(expr.storage_); }
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template <typename X>
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static constexpr X& apply(lazy_value_t<X>& expr)
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{ return hana::get_impl<0>(expr.storage_); }
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template <typename X>
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static constexpr X apply(lazy_value_t<X>&& expr)
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{ return static_cast<X&&>(hana::get_impl<0>(expr.storage_)); }
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};
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//////////////////////////////////////////////////////////////////////////
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// Functor
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//////////////////////////////////////////////////////////////////////////
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template <>
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struct transform_impl<lazy_tag> {
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template <typename Expr, typename F>
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static constexpr auto apply(Expr&& expr, F&& f) {
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return hana::make_lazy(hana::compose(static_cast<F&&>(f), hana::eval))(
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static_cast<Expr&&>(expr)
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);
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}
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};
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//////////////////////////////////////////////////////////////////////////
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// Applicative
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//////////////////////////////////////////////////////////////////////////
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template <>
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struct lift_impl<lazy_tag> {
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template <typename X>
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static constexpr lazy_value_t<typename detail::decay<X>::type>
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apply(X&& x) {
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return {detail::lazy_secret{}, static_cast<X&&>(x)};
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}
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};
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template <>
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struct ap_impl<lazy_tag> {
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template <typename F, typename X>
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static constexpr decltype(auto) apply(F&& f, X&& x) {
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return hana::make_lazy(hana::on(hana::apply, hana::eval))(
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static_cast<F&&>(f), static_cast<X&&>(x)
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);
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}
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};
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//////////////////////////////////////////////////////////////////////////
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// Monad
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//////////////////////////////////////////////////////////////////////////
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template <>
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struct flatten_impl<lazy_tag> {
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template <typename Expr>
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static constexpr decltype(auto) apply(Expr&& expr) {
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return hana::make_lazy(hana::compose(hana::eval, hana::eval))(
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static_cast<Expr&&>(expr)
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);
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}
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};
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//////////////////////////////////////////////////////////////////////////
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// Comonad
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//////////////////////////////////////////////////////////////////////////
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template <>
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struct extract_impl<lazy_tag> {
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template <typename Expr>
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static constexpr decltype(auto) apply(Expr&& expr)
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{ return hana::eval(static_cast<Expr&&>(expr)); }
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};
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template <>
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struct duplicate_impl<lazy_tag> {
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template <typename Expr>
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static constexpr decltype(auto) apply(Expr&& expr)
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{ return hana::make_lazy(static_cast<Expr&&>(expr)); }
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};
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template <>
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struct extend_impl<lazy_tag> {
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template <typename Expr, typename F>
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static constexpr decltype(auto) apply(Expr&& expr, F&& f) {
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return hana::make_lazy(static_cast<F&&>(f))(static_cast<Expr&&>(expr));
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}
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};
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BOOST_HANA_NAMESPACE_END
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#endif // !BOOST_HANA_LAZY_HPP
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