Project Euler Problem 079

import Data.List
import System.IO.Unsafe (unsafePerformIO)

perm :: Eq a => [a] -> [[a]]
perm [] = [[]]
perm l = [x:y | x<-l,y<-perm (delete x l) ]
input :: String
input = unsafePerformIO $ readFile "079keylog.txt"
lists :: [Char]
lists = nub $ sort $ filter (/='\n') input
wordlist :: [String]
wordlist = lines input

check :: Eq a => [a] -> [a] -> Bool
check _ [] = True     
check [] _ = False
check (k:ks) (x:xs) | k == x = check ks xs
check (_:ks) xs = check ks xs

ans1 :: [Char]
ans1 = head [ l | l <- perm lists,all (check l) wordlist]
main :: IO ()
main = print ans1