Class replace

example/tutorial/appendix_mpl.cpp:291–297

template <typename Sequence, typename OldType, typename NewType>
struct replace {
    using type = decltype(hana::replace(
        hana::to_tuple(Sequence{}),
        hana::type_c<OldType>,
        hana::type_c<NewType>
    ));
};

template <typename Sequence, typename Pred, typename NewType>
struct replace_if {