finding the highest common factor/divisor for two integers in haskell

hcf :: Int -> Int -> Int

--handles all cases of zero

hcf 0 0 = undefined 

hcf m 0 = abs m

hcf 0 n = abs n

hcf m n 

    | m == n       = m 

    | m > n        = hcf n (rem m n) 

    | otherwise    = hcf n m