>>71のをArrowで書けばこんな感じ

mapA :: ArrowChoice a => a b c -> a [b] [c]
mapA f = arr listcase >>>
arr (const []) ||| (f *** mapA f >>> arr (uncurry (:)))
where
listcase [] = Left ()
listcase (x:xs) = Right (x,xs)

main :: IO ()
main = runKleisli (Kleisli (const getArgs) >>> mapA (Kleisli readFile) >>> arr concat >>> Kleisli putStr) ()

-- mapAみたいに便利な関数は早く標準ライブラリに入れてほしい