What the fuck MMC?

mr_call(L) = R :-
    semipure Func:lua_func = get_func_upvalue(L),
    (try [Func]
        impure R0 = (Func(L))
        then R = R0
        else
            impure lua_pushboolean(L, no),
            R = 1
        catch_any E ->
            impure lua_pushnil(L),
            impure lua_pushuserdata(L, univ(E)),
            R = 2
    ).



:- semipure func get_func_upvalue(lua) = lua_func.

:- pragma foreign_proc("C", get_func_upvalue(L::in) = (F::out),
    [promise_semipure, will_not_call_mercury], "
    luaMR_getupvalue(L, 1);
    MR_Word ** ptr = lua_touserdata(L, -1);
    F = **ptr;
    lua_pop(L, 1);
").