You are even closer now! What the type checker is trying to tell you is that it doesn't know how to raise Maybe Integer to some power. You apply the ^ operator to two values, f2Maybe (n `div` 2) and 2. Let us give them names: let a = f2Maybe (n `div` 2) :: Maybe Integer b = 2 :: Int in a ^ b You see that the type of a is Maybe Integer. What does this mean? There are only 2 cases to consider. You have Just an integer or you have Nothing. You can use the case construct to write the code for both cases. f2Maybe :: Integer -> Maybe Integer f2Maybe n | n > 0 = Nothing | n == 0 = Just 1 | even n = case f2Maybe (n `div` 2) of Just x -> <fill in> Nothing -> <fill in> | odd n = case f2Maybe (n `div` 2) of Just x -> <fill in> Nothing -> <fill in>