datasort state = | uninit | listening | active | closed absvtype socket (state) typedef port = int typedef addr = string extern fun create (): socket (uninit) extern fun listen (!socket (uninit) >> socket (listening), port): void extern fun accept (!socket (listening) >> socket (active)): void extern fun connect (!socket (uninit) >> socket (active), addr): void extern fun send (!socket (active), int): void extern fun recv (!socket (active)): int extern fun close {s:state} (socket (s)): void implement main0 () = let val sock = create () val _ = listen (sock, 8080) val _ = accept (sock) // block until someone connects val _ = send (sock, 1) val x = recv (sock) in close sock end