John Meacham wrote:

that is what Concurrent is for, Haskell threads, (well GHC threads) are lightweight and can be used for selectlike purposes without too much overhead. I use them quite effectivly for complex networked applications..

see http://haskell.org/ghc/docs/latest/html/base/Control.Concurrent.html

Below is my sample code ; the Net Cats This does not work, because 'accept' fuction of the Network module blocks the whole process, unlike Haskell Standard IO functions which blocks its thread only. How did you work around with complex networked applications ? It would be very helpful if you could give us more detailed advice from your expierience. Network.accept does not seem to be thread friendly. Then how am I going to keep my server from being blocked by accept? \begin{code} import IO import Monad import Network import Control.Exception (finally) import Control.Concurrent hCat inh outh = repeat $ try (hGetLine inh>>=hPutStrLn outh>>hFlush outh) isRight (Right _) = True isRight _ = False dostep actss = filterM ((>>=return.isRight).head) actss theloop [] = return [] theloop actss = dostep actss >>= theloop thd_accept lsock mvar = do actss <- takeMVar mvar print "trying to accept" conn@(h,host,port) <- accept lsock print conn putMVar mvar (hCat h h:actss) thd_accept lsock mvar loopcats mvar = takeMVar mvar >>= dostep >>= putMVar mvar >> loopcats mvar main = withSocketsDo $ do lsock <- listenOn $ PortNumber 9000 print lsock mvar <- newMVar [] forkIO (thd_accept lsock mvar `finally` putMVar mvar []) loopcats mvar `finally` putMVar mvar [] \end{code} -- Ahn Ki-yung