typedef struct Wc <> {
  // all arguments names in this interfaces here
  union Data* wc;       // an implementation
  Block * block;    
  StdData * reuslt;    
  Ack * ack;    
  // codeGear entries of this interface
  __code take(Impl* wc, Block *block,__code next(Ack *ack, ...),__code finish(StdData *result,...);
} Wc;