Hi, Listed below is my first experiment with reactive programming. It is a simple web server written using the Data.Reactive[1] library. The intended interface is given by the runHttpServer function, so the remainder is intended to be internal. I'd be happy to hear comments on any parts of this, but am particularly interested in the following: 1. Is this kind of code what is intended from reactive programming? 2a. I'm not sure about passing the (Handle,...) tuple around. Is there a way to avoid this? 2b. I'm not sure of the best place to handle possible socket exceptions 2c. I'd like to be able to pass a function of type Event Request -> Event Response to runHttpServer, so that reactive programming could be used throughout client code also, but the (Handle,...) tuples seem to be getting in the way. 3. I have a feeling there's a clearer way to write responseSend. Thanks, Levi [1] http://www.haskell.org/haskellwiki/Reactive module Main where import Control.Applicative import Control.Arrow ((&&&),(>>>)) import Control.Concurrent import Control.Monad import Data.Reactive import Network.BSD import Network.HTTP import Network import System.IO import Text.XHtml.Strict type RequestHandler = Request -> Response main = runHttpServer helloWorldHandler helloWorldHandler :: RequestHandler helloWorldHandler _ = Response (2,0,0) "" [] $ prettyHtml helloWorldDoc helloWorldDoc = header << thetitle << "Hello World" +++ body << h1 << "Hello World" runHttpServer r = socketServer >>= runE . handleConnection r socketServer :: IO (Event Handle) socketServer = withSocketsDo $ do (e,snk) <- mkEventShow "Server" sock <- listenOn (PortNumber 8080) forkIO $ forever $ acceptConnection sock $ snk return e handleConnection :: RequestHandler -> Event Handle -> Event (IO ()) handleConnection r = handleToRequest >>> runRequestHandler r >>> responseSend handleToRequest :: Event Handle -> Event (Handle, IO (Result Request)) handleToRequest e = fmap (id &&& receiveHTTP) e responseSend :: Event (Handle, IO (Result Response)) -> Event (IO ()) responseSend e = fmap (\(h,rsp) -> rsp >>= either (putStrLn . show) (respondHTTP h) >> close h) e runRequestHandler :: RequestHandler -> Event (Handle, IO (Result Request)) -> Event (Handle, IO (Result Response)) runRequestHandler r e = fmap hrToHr e where rqhdl :: Result Request -> Result Response rqhdl rq = bindE rq (Right . r) hrToHr :: (Handle, IO (Result Request)) -> (Handle, IO (Result Response)) hrToHr (h,req) = (h, liftA rqhdl req) acceptConnection s k = accept s >>= \(h,_,_) -> forkIO $ k h instance Stream Handle where readLine h = hGetLine h >>= \l -> return $ Right $ l ++ "\n" readBlock h n = replicateM n (hGetChar h) >>= return . Right writeBlock h s = mapM_ (hPutChar h) s >>= return . Right close = hClose