Hi, can someone explain to me why i cannot define meanList as:

meanList :: (Integral a, Fractional b) => [a] -> a

meanList xs = (sumList xs) / (lengthList xs)

I want to restrict the function to only accept lists like [1,2,3] and return answer 2.0

sumList :: (Num a) => [a] -> a

sumList [] = 0

sumList (x:xs) = x + (sumList xs)

lengthList :: (Num a) => [t] -> a

lengthList [] = 0

lengthList (_:xs) = 1 + (lengthList xs)