Find longest word with letters in alphabetical order in Turkish language

longestAlph.hs

import Data.List
import Data.List.Split
import Data.Maybe
import Data.Function (on)

up = ['A','B','C','Ç','D','E','F','G','Ğ','H','I','İ','J','K','L','M','N','O','Ö','P','R','S','Ş','T','U','Ü','V','Y','Z']
low = ['a','b','c','ç','d','e','f','g','ğ','h','ı','i','j','k','l','m','n','o','ö','p','r','s','ş','t','u','ü','v','y','z']

lower xs = map single xs
  where single x = case (x `elemIndex` up) of
                    Nothing -> x
                    Just n -> low !! n

after a b = an <= bn
  where (an, bn) = case (a `elemIndex` low, b `elemIndex` low) of
                    (Just x, Just y) -> (x, y)
                    (_, _) -> (1,0)

firstWord s = (splitOn " " s) !! 0

alph xs = and $ zipWith after xs (drop 1 xs)

main :: IO()
main = do
  file <- readFile "dict.txt"
  let words = lines file
  print $ length words
  let selected = filter alph (map (lower . firstWord) words)
  print $ maximumBy (compare `on` length) selected