gcd.hs

-- Knuth's way
-- from the blog post http://videlalvaro.github.io/2016/10/knuth-first-erlang-programmer.html

gcd m n = f m n 0 1
   where f m n r 1 = f m n (mod m n) 2
         f m n 0 2 = n
         f m n r 2 = f n r r 1