Concurrent hello world in Haskell

gistfile1.hs

module Main (main) where

import Control.Concurrent

main :: IO ()
main = do
    codechan <- newEmptyMVar
    wait <- newEmptyMVar
    myid <- myThreadId
    putStrLn $ "I'm " ++ show myid
    cid <- forkIO $ child codechan wait
    let code = putStrLn ("Hello, " ++ show cid ++ "!")
    putMVar codechan code
    takeMVar wait

child :: MVar (IO ()) -> MVar () -> IO ()
child codechan wait = do
    myid <- myThreadId
    putStrLn $ "I'm " ++ show myid
    code <- takeMVar codechan
    code
    putMVar wait ()