1{-# LANGUAGE Arrows #-} 2 3bar f = proc a -> 4 do b <- f -< a 5 6barbar f g = proc a -> 7 do b <- f -< a 8 returnA -< b 9 10barbaz f g = proc (a, b) -> 11 do c <- f -< a 12 d <- g -< b 13 14bazbar f = proc a -> 15 do a 16 <- 17 f 18 -< 19 a 20 21