module Day1

import System
import System.File
import Data.String
import Text.Parser

parsePair : String -> Maybe (Int, Int)
parsePair pair = do
  num1 <- parseInteger (fst p1)
  num2 <- parseInteger (snd p2)
  pure (num1, num2) where
  p1 = span (/= ' ') pair
  p2 = span (== ' ') (snd p1)

parseStr : String -> List (Int, Int)
parseStr str = do
  nums <- lines str
  maybe [] pure (parsePair nums)
  
transposePairs : List (a, b) -> (List a, List b)
transposePairs [] = ([], [])
transposePairs (x :: xs) = ((fst x) :: (fst rest), (snd x) :: (snd rest)) where
  rest = transposePairs xs

main : IO ()
main = do
  estr <- readFile "data/day1.txt"
  str <- either (die . show) pure estr
  putStrLn $ show $ transposePairs $ parseStr str