Hi Hakell Cafe, I'm struggling to understand my unambitious IterIO code that somehow manages to work. Basically I run an echo server that is supposed to read from a socket line by line and write back to the socket with all the characters in the line reversed: import Control.Exception import Control.Monad import Control.Monad.Trans import Data.IterIO import Data.IterIO.Inum import Network import System.IO import System.IO.Error (isEOFError) import qualified Data.ByteString.Lazy as L import qualified Data.ByteString.Lazy.Char8 as C iterHandle' :: (MonadIO m) => Handle -> IO (Iter L.ByteString m (), Onum L.ByteString m a) iterHandle' = iterHandle main = withSocketsDo $ do sListen <- listenOn (PortNumber 8000) putStrLn "Listening on Port 8000" forkIO $ forever $ do (sSession, hostname, port) <- accept sListen hSetBuffering sSession NoBuffering putStrLn ("Connected to " ++ hostname ++ ":" ++ show port) forkIO $ do (iter, enum) <- iterHandle' sSession enum |$ inumReverseLines .| iter putStrLn "Press <CTRL-D> to quit." exitOnCtrlD inumReverseLines :: (Monad m) => Inum L.ByteString L.ByteString m a inumReverseLines = mkInum $ do line <- lineI return (L.reverse (L.concat [line, C.pack "\n"])) exitOnCtrlD = try getLine >>= either (\e -> unless (isEOFError e) $ ioError e) (const exitOnCtrlD) When I run it, it does this: asdfghc7@hoggy-nn:/home/hoggy$ nc localhost 8000 1234 4321 4321 1234 abcde edcba The red lines are the replies from my echo server. But all I've done is: enum |$ inumReverseLines .| iter inumReverseLines = mkInum $ do line <- lineI return (L.reverse (L.concat [line, C.pack "\n"])) No attempt was made to reverse more than one line - at least as far as I can see. What have I done wrong that it should work so well? Also, is there a better way to do this? Cheers, -John