typedef struct Stack<Impl>{
        union Data* stack;
        union Data* data;
        union Data* data1;
        __code whenEmpty(...);
        __code clear(Impl* stack,__code next(...));
        __code push(Impl* stack,union Data* data, __code next(...));
        __code pop(Impl* stack, __code next(union Data*, ...));
        __code pop2(Impl* stack, union Data** data, union Data** data1, __code next(union Data**, union Data**, ...));
        __code isEmpty(Impl* stack, __code next(...), __code whenEmpty(...));
        __code get(Impl* stack, union Data** data, __code next(...));
        __code get2(Impl* stack,..., __code next(...));
        __code next(...);
} Stack;