Haskell script using fsnotify to watch for filesystem events in given dir

WatchDir.hs

#!/usr/bin/env stack
-- stack script --resolver lts-10.9 --package fsnotify
{-# LANGUAGE OverloadedStrings #-}

import           Control.Concurrent (threadDelay)
import           Control.Monad      (forever)
import           System.Environment (getArgs)
import           System.FSNotify    (watchTree, withManager)

main :: IO ()
main = do
    [dir] <- getArgs
    withManager $ \mgr -> do
       watchTree mgr dir (const True) print 
       forever $ threadDelay 1000000