typedef struct Wc <> {
  // all arguments names in this interfaces here
  union Data* wc;       // an implementation
  WcResult* result;    
  // codeGear entries of this interface
  __code openFile(Impl* wc, __code next(...));
  __code countUp(Impl* wc, __code next(WcResult* result, ...));
  __code next(...);
} Wc;