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/*!
@file
Defines `boost::hana::prefix`.
@copyright Louis Dionne 2013-2017
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_PREFIX_HPP
#define BOOST_HANA_PREFIX_HPP
#include <boost/hana/fwd/prefix.hpp>
#include <boost/hana/append.hpp>
#include <boost/hana/chain.hpp>
#include <boost/hana/concept/monad_plus.hpp>
#include <boost/hana/config.hpp>
#include <boost/hana/core/dispatch.hpp>
#include <boost/hana/functional/partial.hpp>
#include <boost/hana/lift.hpp>
BOOST_HANA_NAMESPACE_BEGIN
//! @cond
template <typename Xs, typename Pref>
constexpr auto prefix_t::operator()(Xs&& xs, Pref&& pref) const {
using M = typename hana::tag_of<Xs>::type;
using Prefix = BOOST_HANA_DISPATCH_IF(prefix_impl<M>,
hana::MonadPlus<M>::value
);
#ifndef BOOST_HANA_CONFIG_DISABLE_CONCEPT_CHECKS
static_assert(hana::MonadPlus<M>::value,
"hana::prefix(xs, pref) requires 'xs' to be a MonadPlus");
#endif
return Prefix::apply(static_cast<Xs&&>(xs), static_cast<Pref&&>(pref));
}
//! @endcond
template <typename M, bool condition>
struct prefix_impl<M, when<condition>> : default_ {
template <typename Xs, typename Z>
static constexpr decltype(auto) apply(Xs&& xs, Z&& z) {
return hana::chain(static_cast<Xs&&>(xs),
hana::partial(hana::append, hana::lift<M>(static_cast<Z&&>(z))));
}
};
BOOST_HANA_NAMESPACE_END
#endif // !BOOST_HANA_PREFIX_HPP
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