{-# LANGUAGE Arrows #-}

foo f = proc a ->
  do f -< a

bar f = proc a ->
  do b <- f -< a

barbar f g = proc a ->
  do b <- f -< a
     returnA -< b

barbaz f g = proc (a, b) ->
  do c <- f -< a
     d <- g -< b

bazbar f = proc a ->
  do a
       <-
       f
       -<
       a

bazbaz f g h = proc (a, b, c) ->
  do x
       <- f b -< a
     y <-
       g b -< b
     z <-
       h
         x
         y
       -< (
           a,
           b,
           c
       )
     returnA -<
       (x, y, z)