Wordcount in Haskell

gistfile1.hs

module Main where

import Data.List
import qualified Data.Text.Lazy.IO as TIO
import qualified Data.Text.Lazy as T
import qualified Data.Map.Strict as M
import System.Environment
import Control.Monad

type Str = T.Text

wordcount :: Str -> M.Map Str Int
wordcount str = foldl' (flip $ M.alter incr) M.empty (T.words str)
    where
        incr Nothing = Just 1
        incr (Just count) = Just (count + 1)

main :: IO ()
main = do
    args <- getArgs
    when (length args == 1) $ do
        content <- TIO.readFile $ head args
        print $ M.size $ wordcount content