aoc2021/app/D2P2.hs

module Main where

main :: IO ()
main = interact solution

solution :: String -> String
solution = show
         . multhem
         . foldl applymove (0, 0, 0)
         . map ((\[a, b] -> (head a, read b :: Int)) . words)
         . lines
    where
      applymove :: (Int, Int, Int) -> (Char, Int) -> (Int, Int, Int)
      applymove (x, y, a) (d, v) = case d of
        'f' -> (x + v, y + v * a, a)
        'd' -> (x, y, a + v)
        'u' -> (x, y, a - v)
        _   -> undefined -- unreachable
      multhem :: (Int, Int, Int) -> Int
      multhem (a, b, _) = a * b