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;