You can abstract this pattern:
-- runs its argument in an infinite loop, and returns an action that stops the loop daemon :: IO () -> IO (IO ()) daemon action = do stopvar <- atomically $ newTVar False let run = do stop <- atomically $ readTVar stopvar if stop then return () else (action >> run) forkIO run return (atomically $ writeTVar stopvar True)
TVars are overkill here, actually, an IORef would be just fine, I think.
Luke
Thanks, Luke! Why do you write "return (atomically $ writeTVar stopvar True)" in the end? Actually, I'm more interested in technical details how to communicate from shell with background process - how to send commands to it. Currently looking into POSIX libraries hope to find answers there... Also, maybe a FIFO-pipe-file would solve my problem. Imagine writing a command in it, while one of daemon's thread is locked-while-awaits for anything to come out from the other side of the pipe... Belka -- View this message in context: http://www.nabble.com/how-to-implement-daemon-start-and-stop-directives--tp2... Sent from the Haskell - Haskell-Cafe mailing list archive at Nabble.com.