Project Euler Problem 067

import System.IO.Unsafe

input :: String
input = unsafePerformIO $ readFile "067triangle.txt"
lis :: [[Integer]]
lis = map (map read . words) $ lines input
ans1 :: [Integer]
ans1 = foldr1 f lis
f :: (Num t, Ord t) => [t] -> [t] -> [t]
f xx acc = imp xx acc where
  imp [x] (y:z:_) = [x + max y z]
  imp (x:xs) (y:z:zs) = x + max y z : imp xs (z:zs)
-- 7273
main :: IO ()
main = print ans1