Maybeを潰すのは型的に合っていないと思う

data A
data B
data C
f :: A -> IO (Maybe B)
f = undefined
g :: B -> IO (Maybe C)
g = undefined

h :: A -> IO (Maybe C)
h x = runMaybeT $ MaybeT (f x) >>= (\y -> MaybeT (g y))

h' :: A -> IO (Maybe C)
h' = runMaybeT . (MaybeT . f >=> MaybeT . g)