Haskell I/O sample program (Euler 18)

maximum_path_sum.hs

import System.Environment(getArgs)

main = do args <- getArgs
          if length args > 0
          then do inpstr <- readFile $ head args
                  putStrLn $ show (maxPathSum (parseData inpstr))
          else putStrLn "I need a filename with triangle data!"

parseData s = map (\s -> map read (words s)) $ lines s

maxPathSum list =
  let addListsFold upper lower = zipWith (+) upper $ maxList lower
        where
          maxList (x:[])   = []
          maxList (x:y:xs) = (max x y) : (maxList $ y:xs)

  in head $ foldr1 addListsFold list