haskell script to recursively save directory names to file

extractDirectoryNames.hs

{-# LANGUAGE  OverloadedStrings #-}
import Data.ByteString as B hiding (filter)
import Data.Set (fromList, member)
import Data.Text   as T hiding (filter)
import Data.Text.Encoding
import System.Directory
import System.FilePath.Windows

-- work around encoding problems
main = recursiveDirectoryNames "."

recursiveDirectoryNames source = listDirectory source >>= action

 where
  action [] = return ()
  action target =
    mapM_
        ( B.appendFile "results.txt". encodeUtf8. T.pack. (++ linebreak))
        (directories target)
      >> mapM_
           (recursiveDirectoryNames . (source </>)) (directories target)
  linebreak   = "\r\n"
  directories = filter $ \entry -> not (hasExtension  || (entry `member` exceptions))
  exceptions = fromList ["LICENSE"]