unison/unison-src/tests/console1.u

-- This confusingly gives an error that
-- it doesn't know what `Console.simulate` is.

structural ability State s where
  get : {State s} s
  set : s -> {State s} ()

structural ability Console where
  read : {Console} (Optional Text)
  write : Text -> {Console} ()

fst = cases Tuple.Cons a _ -> a

snd = cases Tuple.Cons _ (Tuple.Cons b _) -> b

simulate : Request Console a -> {State ([Text], [Text])} a
simulate = cases
  { pure } -> pure
  {Console.read -> k} -> handle
      io = State.get
      ins = fst io
      outs = snd io
      State.set (drop 1 ins, outs)
      k (at 0 ins)
    with simulate

  {Console.write t -> k} -> handle
      io = State.get
      ins = fst io
      outs = snd io
      State.set (ins, outs ++ [t])
      k ()
    with simulate

e = 'let handle
    use Console read write
    use Optional Some None
    write "What's your name?"
    match read with
      Some name -> write ("Hello" ++ name)
      None -> write "Fine, be that way."
  with simulate