wc written in Haskell using enumerator

WCEnumerator.hs

import qualified Data.ByteString as BS
import qualified Data.ByteString.Internal as BS (c2w, w2c) 
import Data.Enumerator hiding (head)
import qualified Data.Enumerator.Binary as EB
import qualified Data.Enumerator.List as EL
import System.Environment

countLines :: Iteratee BS.ByteString IO Int
countLines = do
	bs <- EL.head
	case bs of
		Nothing -> return 0
		Just string -> do
			numLines <- countLines
			return $ (BS.count (BS.c2w '\n') string) + numLines

main = do
	args <- getArgs
	let filename = head args
	numLines <- run_ (EB.enumFile filename $$ countLines)
	print numLines