example multihandler in Unison

pipe.u

-- An example multihandler.
-- Pipe messages out of the first argument computation into the second.
pipe : Request (Send m) () -> Request (Receive m) a ->{Abort} a
pipe sender receiver =
  case receiver of
    { Receive.receive -> kr } ->
      case sender of
        { Send.send m -> ks } -> pipe (step ks) (step '(kr m))
        { _ } -> Abort.abort
    { a } -> a

-- Utility function to get the first ability request emitted by a computation.
step : '{e} a -> Request e a
step k =
  h : Request e a -> Request e a
  h r = r
  handle !k with h

pipe' : ('{Send m} ()) -> ('{Receive m} a) ->{Abort} a
pipe' sender receiver =
  handle !receiver with (pipe (step sender))

ability Send a where
  send : a -> ()

ability Receive a where
  receive : a

ability Abort where
  abort : a