typedef struct Queue<>{
    union Data* queue;
    union Data* data;

    __code whenEmpty(...);
    __code clear(Impl* queue, __code next(...));
    __code put(Impl* queue, union Data* data, __code next(...));
    __code take(Impl* queue, __code next(union Data* data, ...));
    __code isEmpty(Impl* queue, __code next(...), __code whenEmpty(...));
    __code next(...);
} Queue;