Function next

example/optional/applicative.cpp:12–12

constexpr char next(char c) { return c + 1; }

static_assert(hana::ap(hana::just(next), hana::just('x')) == hana::just('y'), "");
BOOST_HANA_CONSTANT_CHECK(hana::ap(hana::nothing, hana::just('x')) == hana::nothing);