Haskell Networking Example

2 Apr 2003


      Hello All,
  Here is an example of using haskell networking
operations for those interested.  The implementation
is a simple echo server.

echoclient.hs:

module Main( main ) where

import Network
import IO
import Control.Concurrent

main :: IO ()
main =  withSocketsDo $ --For windows compatibility
  do
    handle <- connectTo "localhost" (PortNumber 2048)
    input <- getContents
    sequence_ $ map ( \a -> do 
      hPutStr handle $ a ++ "\n"
      hFlush handle ) $ lines input
    hClose handle

echoserver.hs:

module Main( main ) where

import Network
import IO
import Control.Concurrent

main :: IO ()
main = withSocketsDo $ --For windows compatibility
  do
    theSocket <- listenOn (PortNumber 2048)
    sequence_ $ repeat $ acceptConnectionAndFork
theSocket
  where
    acceptConnectionAndFork :: Socket -> IO ()
    acceptConnectionAndFork theSocket = do
      connection <- accept theSocket
      let (handle, hostname, portnumber ) = connection
      putStr ("("++ hostname ++ ":" ++ (show
portnumber) ++ "): Open\n" )
      forkIO (echoServer connection)
      return ()

echoServer :: (Handle, String, PortNumber) -> IO ()
echoServer (handle, hostname, portnumber ) = do
  a <- hGetContents handle
  putStr $ foldr (++) "" $ map (\a -> "(" ++ hostname
++ ":" 
          ++ (show portnumber) ++ "): Msg " ++ (show
a) ++ "\n" ) $ lines a
  putStr ("("++ hostname ++ ":" ++ (show portnumber)
++ "): Close\n" )

Makefile:

all: echoclient echoserver

echoclient: echoclient.hs
        ghc -package network echoclient.hs -o
echoclient

echoserver: echoserver.hs
        ghc -package network echoserver.hs -o
echoserver

clean:
        rm *.o *.hi echoclient echoserver

Haskell Networking Example

David Sankel