[[ProjectEular]]

 -- Problem 8
 
 module Main (main) where
 
 import qualified List   (tails)
 import qualified Char   (digitToInt)
 import qualified List (tails)
 import qualified Char (digitToInt)
 
 main :: IO ()
 main = do
     digits_str <- getContents
     print $ problem8 $ to_digits digits_str
 
 problem8 :: [Int] -> Int
 problem8 = maximum . map product . lists_5digits
 
 -- [[7,3,1,6,7], [3,1,6,7,1], [1,6,7,1,7], ..., [6,3,4,5,0]]
 lists_5digits :: [Int] -> [[Int]]
 lists_5digits = filter (\xs -> length xs == 5) . map (take 5) . List.tails
 
 to_digits :: String -> [Int]
 to_digits = map Char.digitToInt . concat . lines
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