1{-# LANGUAGE Arrows #-} 2 3bar f = proc a -> do 4 b <- f -< a 5 6barbar f g = proc a -> do 7 b <- f -< a 8 returnA -< b 9 10barbaz f g = proc (a, b) -> do 11 c <- f -< a 12 d <- g -< b 13 14bazbar f = proc a -> do 15 a <- 16 f 17 -< 18 a 19