cout in Haskell

cout.hs

{-# LANGUAGE MultiParamTypeClasses, FlexibleInstances, IncoherentInstances #-}

class Cout a r where
  (<<) :: IO String -> a -> IO r

instance Cout [Char] [Char] where
  lm << x = fmap (++ x) lm

instance Cout [Char] () where
  lm << x = lm >>= putStr . (++ x)

instance Show a => Cout a [Char] where
  lm << x = fmap (++ show x) lm

instance Show a => Cout a () where
  lm << x = lm >>= putStr . (++ show x)

cout :: IO [Char]
cout = return ""

main :: IO ()
main = do
  cout << "Hello world " << 5 << True << "\n" :: IO ()
  return ()