Take all the possible letter substitutions in a password, and append to it a list of possible years

transform.hs

import System.Environment (getArgs)
import Data.Map (fromList, findWithDefault)
import qualified Data.Set as S

nub = S.toList . S.fromList

applyIf f = (\x flag -> if flag then f x else x)

flagCombinations n = sequence $ replicate n [True, False]

leet x = nub $ map (zipWith (applyIf substitute) x) $ flagCombinations $ length x

substitutions = fromList [('o','0'), ('a','4'), ('s','5')]
substitute x = findWithDefault x x substitutions

years = [1900..2014]
appendYears x = map ((x ++) . show) years

transform = concatMap (concatMap appendYears . leet)

main = do
  infile:_ <- getArgs
  passwords <- fmap lines $ readFile infile
  putStrLn  $ unlines $ transform passwords