text: /*!
  @file
  Defines `boost::hana::chain`.
  
  @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_CHAIN_HPP
  #define BOOST_HANA_CHAIN_HPP
  
  #include <hana/fwd/chain.hpp>
  
  #include <hana/concept/monad.hpp>
  #include <hana/config.hpp>
  #include <hana/core/dispatch.hpp>
  #include <hana/flatten.hpp>
  #include <hana/transform.hpp>
  
  
  BOOST_HANA_NAMESPACE_BEGIN
      //! @cond
      template <typename Xs, typename F>
      constexpr decltype(auto) chain_t::operator()(Xs&& xs, F&& f) const {
          using M = typename hana::tag_of<Xs>::type;
          using Chain = BOOST_HANA_DISPATCH_IF(chain_impl<M>,
              hana::Monad<M>::value
          );
  
      #ifndef BOOST_HANA_CONFIG_DISABLE_CONCEPT_CHECKS
          static_assert(hana::Monad<M>::value,
          "hana::chain(xs, f) requires 'xs' to be a Monad");
      #endif
  
          return Chain::apply(static_cast<Xs&&>(xs), static_cast<F&&>(f));
      }
      //! @endcond
  
      template <typename M, bool condition>
      struct chain_impl<M, when<condition>> : default_ {
          template <typename Xs, typename F>
          static constexpr auto apply(Xs&& xs, F&& f) {
              return hana::flatten(hana::transform(static_cast<Xs&&>(xs),
                                                   static_cast<F&&>(f)));
          }
      };
  BOOST_HANA_NAMESPACE_END
  
  #endif // !BOOST_HANA_CHAIN_HPP
  