Haskell daemon

Seo sampla daemon Haskell:

import System.Exit
import System.IO.Unsafe
import System.Posix.Signals
import Control.Concurrent

termReceived = unsafePerformIO (newMVar False)

handleTERM :: IO ()
handleTERM = do
  swapMVar termReceived True
  return ()

wrapup :: IO ()
wrapup = do
  -- Shut down cleanly
  putStrLn "shutting down"
  return ()

doWork :: IO ()
doWork = do
  -- For now, just pretend we're doing something
  putStrLn "working"
  threadDelay 20000

loop :: IO ()
loop = do
  timeToStop <- readMVar termReceived
  if timeToStop
    then wrapup
    else do 
      doWork
      loop


main = do
  installHandler sigTERM (Catch handleTERM) Nothing
  loop