Not Quite Lisp

import Data.List;
import Data.Maybe;
import Text.Printf;

parenToOffset :: Char -> Int
parenToOffset '(' = 1
parenToOffset ')' = -1
parenToOffset _   = 0

toCurrentLevel :: [Int] -> [Int]
toCurrentLevel = reverse . go [0]
  where
    go :: [Int] -> [Int] -> [Int]
    go acc     []     = acc
    go []      xs     = go [0] xs
    go (a:acc) (x:xs) = go (a + x : acc) xs

levelsAtIndex :: String -> [Int]
levelsAtIndex = toCurrentLevel . fmap parenToOffset

main :: IO ()
main = do
    contents <- getContents
    let levels = levelsAtIndex contents
    printf "Task 1: %d\n" $ last levels
    printf "Task 2: %d\n" $ fromMaybe (-1) $ elemIndex (-1) levels