module Main where

import Control.Concurrent

main :: IO ThreadId
main = do theTalk <- newEmptyMVar :: IO ( MVar String )
          forkIO( chris_proc theTalk )
          forkIO( kelly_proc theTalk )

kelly_proc :: MVar String -> IO ()
kelly_proc theTalk = do talk <- takeMVar theTalk
                        putStrLn talk
                        putMVar theTalk "Hello, can I speak to Chris?"
                        yield
                        talk <- takeMVar theTalk
                        putStrLn talk
                        putMVar theTalk "Chris, this is Kelly from ACME company\n and we are having a special on..."
                        yield
	                talk <- takeMVar theTalk
                        putStrLn talk
                        putMVar theTalk "But this is a great deal and ..."
                        yield
 			talk <- takeMVar theTalk
			putStrLn talk                        

chris_proc :: MVar String -> IO ()
chris_proc theTalk = do putMVar theTalk "Hello?"
                        yield
                        talk <- takeMVar theTalk
                        putStrLn talk
                        putMVar theTalk "This is Chris"
                        yield
                        talk <- takeMVar theTalk
                        putStrLn talk
                        putMVar theTalk "Excuse me, but I am really not interested."
                        yield
                        talk <- takeMVar theTalk
                        putStrLn talk
                        putMVar theTalk "I am hanging up now;\n goodbye."
		        return ()