How do you define a function of signature h :: M Int -> M Int -> M Int so that h (M x) (M y) = M (x+y) without unwrapping the monad? http://stackoverflow.com/questions/15035468/how-do-you-define-a-function-of-signature-h-m-int-m-int-m-int-so-that-h

gistfile1.txt

g x y = (return . (+x)) =<< y
 = (=<<) (return . (+x)) y
 = ((=<<) . (return .)) ((+) x) y
 = (=<<) . (return .) . (+) $ x y

h mx my = mx >>= (\x ->
          my >>= (\y ->
          return (x+y) ))

h mx my = do x <- mx
             y <- my
             return (x+y)

h mx my = liftM2 (+) mx my