--
-- Concurrent Haskell for beginners 
--

import Random(randomRIO)
import Concurrent

forN :: Int-> IO a-> IO ()
forN n a = if n== 0 then return () else a >> forN (n-1) a

echo :: MVar ()-> String-> IO ()
echo flag p = do takeMVar flag
                 putStrLn ("Please enter line "++p)
      	         line <- getLine
	         putMVar flag ()
	         randomRIO (1,100) >>= \n-> forN n (putStr (p++ line))
	         yield
                 echo flag p
	
main :: IO ()
main = do flag <- newMVar () 
          forkIO (echo flag "1") >> echo flag "2"