Chaddaï Fouché
To use a typeclass there is pretty strange and doesn't have much advantage, it would be much easier and nicer to just write start to take some functions as parameters...
Doh! Yes, I kind of overlooked the obvious there. Thank you so much! Here's my new version, in case anyone Googles this. ----- Daemon.hs ----- module Daemon where import System.Exit import System.IO.Unsafe import System.Posix.Signals import Control.Concurrent termReceived = unsafePerformIO (newMVar False) handleTERM :: IO () handleTERM = swapMVar termReceived True >> return () loop :: (a -> IO a) -> (a -> IO ()) -> a -> IO (Maybe a) loop work finalise d = do timeToStop <- readMVar termReceived if timeToStop then finalise d >> return Nothing else work d >>= loop work finalise start -- | This function will be invoked when the daemon starts. :: IO a -- | This function will be invoked in the main loop. -> (a -> IO a) -- | This function will be invoked when the daemon shuts down. -> (a -> IO ()) -- | The result will always be Nothing. -> IO (Maybe a) start initialise work finalise = installHandler sigTERM (Catch handleTERM) Nothing >> initialise >>= loop work finalise ----- CountingExample.hs ----- module CountingExample where import Daemon initialise = do putStrLn "Starting up" return 0 work i = do putStrLn (show i) return (i+1) finalise i = do putStrLn "Shutting down" return () main = start initialise work finalise