Hello,World!

HelloWorld.hs

module Main where

import Network ( withSocketsDo, listenOn, PortID(PortNumber), connectTo )
import Network.Socket ( accept, send, close, recvLen )
import Control.Concurrent ( forkIO, threadDelay )
import System.IO ( hClose )
import Control.Monad ( void )
import Control.Exception ( bracket )

main :: IO ()
main = withSocketsDo $ do
  let port = PortNumber $ toEnum 3000
  let wait = void . forkIO . bracket (connectTo "localhost" port) hClose . const . threadDelay
  bracket (listenOn port) close $ \lis -> do
    wait 3000000
    bracket (accept lis) (close . fst) $ \(sock, _) ->
      void $ forkIO $ do
        threadDelay 1000000
        void $ send sock "Hello,World!"
    wait 2000000
    bracket (accept lis) (close . fst) $ \(sock, _) ->
      recvLen sock 1024 >>= putStrLn . fst