I've written an echo server using just sockets:

import Control.Concurrent

import Control.Exception

import Control.Monad

import System.IO.Error (isEOFError)

main = withSocketsDo $ do

sListen <- listenOn (PortNumber 8000)

putStrLn "Listening on Port 8000"

forkIO $ forever $ do

(sSession, hostname, port) <- accept sListen

putStrLn ("Connected to " ++ hostname ++ ":" ++ show port)

forkIO $ echoLines sSession

putStrLn "Press <CTRL-D> to quit."

echoLines h = try (hGetLine h) >>= either

(\e -> do { hClose h; if isEOFError e then print e else ioError e})

(\l -> do { hPutStrLn h l; hFlush h; echoLines h})

exitOnCtrlD = try getLine >>= either

(\e -> unless (isEOFError e) $ ioError e)

When I send text to it, it will echo it back immediately after my newline.

I then modified it to user IterIO:

import Control.Concurrent

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

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

putStrLn ("Connected to " ++ hostname ++ ":" ++ show port)

forkIO $ do

(iter, enum) <- iterHandle' sSession

enum |$ iter

return ()

putStrLn "Press <CTRL-D> to quit."

exitOnCtrlD

exitOnCtrlD = try getLine >>= either

(\e -> unless (isEOFError e) $ ioError e)

(const exitOnCtrlD)

It works, however it doesn't send anything back to me until end of file.

I fixed that problem with my sockets version by flushing after each line, but I don't know if IterIO will let me flush on every newline.