C++ struct templates in local scope

cursed.cpp

#include <type_traits>

#define DEFINE_LOCAL_VALUE_TEMPLATE(name, value) \
    [](auto __t){ \
        using name = std::remove_reference_t<decltype(__t)>; \
        return value; \
    }

#define DEFINE_LOCAL_TYPE_TEMPLATE(name, ...) \
    [](auto __t){ \
        using name = std::remove_reference_t<decltype(__t)>; \
        __VA_ARGS__ *__s = nullptr; \
        return *__s; \
    }

#define CALL_LOCAL_VALUE_TEMPLATE(name, arg_type) \
    name(std::declval<arg_type>())

#define CALL_LOCAL_TYPE_TEMPLATE(name, arg_type) \
    decltype(CALL_LOCAL_VALUE_TEMPLATE(name, arg_type))

void wat() {
    struct nil {};
    auto prepend = DEFINE_LOCAL_VALUE_TEMPLATE(Head,
        DEFINE_LOCAL_TYPE_TEMPLATE(Tail,
            struct {
                using type = Head;
                using next = Tail;
            }
        )
    );

    using list_of_integral_types =
        CALL_LOCAL_TYPE_TEMPLATE(CALL_LOCAL_VALUE_TEMPLATE(prepend, char),
        CALL_LOCAL_TYPE_TEMPLATE(CALL_LOCAL_VALUE_TEMPLATE(prepend, short),
        CALL_LOCAL_TYPE_TEMPLATE(CALL_LOCAL_VALUE_TEMPLATE(prepend, int),
        CALL_LOCAL_TYPE_TEMPLATE(CALL_LOCAL_VALUE_TEMPLATE(prepend, long),
        CALL_LOCAL_TYPE_TEMPLATE(CALL_LOCAL_VALUE_TEMPLATE(prepend, long long),
        nil)))));

    auto silly_pair = DEFINE_LOCAL_TYPE_TEMPLATE(T,
        struct {
            T _1;
            T _2;
        }
    );

    using int_pair =
        CALL_LOCAL_TYPE_TEMPLATE(silly_pair, list_of_integral_types::next::next::type);

    constexpr int_pair p{
        42,
        1337
    };

    static_assert(p._1 + p._2 == 1379);
}

int main() {
    wat();
}