class.hpp

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#pragma once
#include <mpc/functional/partial.hpp>
 
namespace mpc {
  // monad_trans
  // https://hackage.haskell.org/package/transformers-0.6.0.2/docs/Control-Monad-Trans-Class.html
 
  template <class>
  struct monad_trans_traits;
 
  template <class TR>
  concept monad_trans = requires {
    monad_trans_traits<std::remove_cvref_t<TR>>::lift;
  };
 
  // Methods required for the class definition.
 
  namespace detail {
    template <class TR>
    struct lift_op {
      template <class M>
      constexpr auto operator()(M&& m) const noexcept(
      noexcept(   monad_trans_traits<std::remove_cvref_t<TR>>::lift(std::forward<M>(m))))
      -> decltype(monad_trans_traits<std::remove_cvref_t<TR>>::lift(std::forward<M>(m)))
      { return    monad_trans_traits<std::remove_cvref_t<TR>>::lift(std::forward<M>(m)); }
    };
  } // namespace detail
 
  inline namespace cpo {
    template <class TR>
    inline constexpr partial<detail::lift_op<TR>> lift{};
  } // namespace cpo
} // namespace mpc