Project Euler Problem #14

euler14.hs

import Data.List (foldl')

collatz :: Int -> [Int]
collatz n
  | n == 1    = [1]
  | even n    = n : collatz (n `div` 2)
  | otherwise = n : collatz (3 * n + 1)

compareCollatzTuple :: (Int, Int) -> Int -> (Int, Int)
compareCollatzTuple acc x =
  if lxt > snd acc then
    (x, lxt)
  else
    acc
  where
    lxt  = length $ collatz x

euler14 :: Int
euler14 = fst $ foldl' compareCollatzTuple (0,0) [1..999999]