Code doesn't have to look like that, look at the Haskell version: gcd x y | x == y = x | x > y = gcd (x - y) y | otherwise = gcd x (y

Code doesn't have to look like that, look at the Haskell version: gcd x y | x == y = x | x > y = gcd (x - y) y | otherwise = gcd x (y - x) Much more close to the math notation.