On Tue, 14 Jun 2011 13:10:36 -0400
David McBride
It probably has to do more with parenthesis than anything:
forever $ atomically $ readTchan chan >>= print forever $ (atomically $ readTchan chan) >>= print
That might work. Once you get the types to line up, that should work.
Thanks for the hint. I finally got it compiled and almost working. The code is now like this: {-# LANGUAGE ScopedTypeVariables #-} import GHC.Conc.Sync import System.IO import System.Environment import System.Process import Control.Monad import Control.Concurrent.STM.TChan import Control.Exception.Base import Text.Printf import Prelude hiding (catch) makeThread :: Handle -> TChan String -> IO ThreadId makeThread handle chan = forkIO $ forever (do eof <- hIsEOF handle unless eof $ hGetLine handle >>= atomically . writeTChan chan) `catch` (\(e :: SomeException) -> return ()) issueCmd :: String -> [String] -> IO () issueCmd cmd parms = do (_ ,Just hout ,Just herr ,_) <- createProcess (proc cmd parms) { std_out = CreatePipe, std_err = CreatePipe } chan <- newTChanIO :: IO (TChan String) _ <- makeThread hout chan _ <- makeThread herr chan forever $ atomically (readTChan chan) >>= printf "%s\n" main :: IO () main = do args <- getArgs let cmd = head args let parms = tail args issueCmd cmd parms print "Done" If I run this with a command the command's output will be printed but after that the program is hanging, and top shows 100% cpu usage. "Done" will never be printed. Any idea what I have to add to prevent it from hanging? -- Thanks, Manfred