aoc2023_day01.hs

import Control.Applicative ((<|>), Alternative)
import Control.Arrow ((&&&))
import Control.Monad (guard)
import Data.Bifunctor (bimap)
import Data.Char (digitToInt, isDigit)
import Data.List (findIndex, tails, isPrefixOf)
import Data.Maybe (catMaybes, listToMaybe)

parse :: Alternative f => Char -> f Int
parse s = guard (isDigit s) *> pure (digitToInt s)

numbers :: [String]
numbers = ["one", "two", "three", "four", "five", "six", "seven", "eight", "nine"]

parse2 :: String -> Maybe Int
parse2 t = (listToMaybe t >>= parse) <|> (1+) <$> findIndex (`isPrefixOf` t) numbers

main :: IO ()
main = ((bimap >>= id) (sum . map (extract . catMaybes)) . (map (map parse) &&& map (map parse2 . tails)) . lines <$> getContents) >>= print
  where extract ls = 10 * head ls + last ls