data State = Idle | Waiting | Connected

data Message = Hello Int | Data Int | Close

match classify (s : State) (m : Message) : Int =
  | Idle (Hello n) -> n
  | Idle (Data n) -> n
  | Idle Close -> 0
  | Waiting (Hello n) -> n
  | Waiting (Data n) -> n
  | Waiting Close -> 0
  | Connected (Hello n) -> n
  | Connected (Data n) -> n
  | Connected Close -> 0