module Main where import System Environment getArgs getProgName import

module Main where

import System.Environment (getArgs, getProgName)
import Control.Concurrent (forkIO)
import Network (Socket, PortID(PortNumber), withSocketsDo, 
                listenOn, accept)
import System.IO (hPutStrLn, hGetLine, hFlush)
import Control.Monad (forever)

main = withSocketsDo $ do
  args <- getArgs
  prog <- getProgName
  case args of
    [port] -> do
      socket <- listenOn $ PortNumber (fromIntegral (read port :: Int))
      putStrLn $ "Listening for pings on " ++ port
      handleRequest socket
    _ ->
      putStrLn $ "usage: " ++ prog ++ " <port>"

handleRequest s = do
  (handle, _, _) <- accept s
  forkIO $
    forever $ do
      input <- hGetLine handle
      processPing (hPutStrLn handle) (init input)
      hFlush handle
  handleRequest s

processPing f msg = do
  case msg of
    "ping" -> f "pong!"
    _      -> f "Did you mean `ping'?"