AoC/2023/day09/day09.hs

import Control.Arrow

main :: IO ()
main = do
  input <- parse <$> readFile "input"
  print $ day09 input

parse :: String -> [[Int]]
parse = map (map read . words) . lines

day09 :: [[Int]] -> (Int, Int)
day09 =
  (sum *** sum) .
  unzip .
  map
    ((sum . map last &&& foldr1 (-) . map head) .
     takeWhile (not . null) . iterate (zipWith (-) =<< tail))