static constexpr decltype(auto) apply(Xs&& xs, F&& f) { constexpr std::size_t N = decltype(hana::length(xs))::value; return unpack_helper(static_cast<Xs&&>(xs), static_cast<F&&>(f), std::make_index_sequence<N>{}); }
static constexpr auto unpack_impl(R r, F f) { auto size = minus(r.to, r.from); return unpack_helper(f, r.from, detail::std::make_integer_sequence<decltype(r.from()), size()>{}); }