Problem8

gistfile1.hs

digs :: Integral x => x -> [x]
digs 0 = []
digs x = x `mod` 10 : digs (x `div` 10)

problem8 :: (Integral a) => a -> a
problem8 a = problem8' (digs a)

problem8' :: (Integral a) => [a] -> a
problem8' xs
  | inputLength < 13  = 0
  | otherwise         = max (product input)  (problem8' (tail xs))
  where input = take 13 xs
        inputLength = length input