{-# LANGUAGE Arrows #-}

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