advent-of-code/three.hs

import           Data.Char

splitlist :: [a] -> ([a],[a])
splitlist list = (take n list,drop n list)
  where n = (length list) `div` 2

inBoth :: (Eq a) => ([a],[a]) -> [a]
inBoth (first,second) = do
  inFirst <- first
  if (inFirst `elem` second) then return inFirst else []

toPriority :: Char -> Int
toPriority char = ordNum - (substract ordNum)
  where
    ordNum = (ord char)
    substract n
      | n < 97 = 38
      | otherwise = 96

main = do
  input <- readFile "three-input.txt"
  print $sum $  map (toPriority . head . inBoth . splitlist ) $ lines input