{-# 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
