{- The dining philosophers, implemented with MVars -}

module Main where


import Concurrent -- hiding (QSem,newQSem, waitQSem, signalQSem)
import System(getArgs)

forever :: IO a -> IO a
forever a = a >> forever a

block :: IO ()
block = newEmptyMVar >>= takeMVar -- blocks calling thread indefinitely

wait :: IO ()
wait = threadDelay 10000

philo :: [MVar ()] -> Int-> IO ()
philo chopsticks i = 
   let num_phil = length (chopsticks) 
   in do putStrLn ("Phil #"++(show i)++" thinks...")
	 wait
         takeMVar (chopsticks !! i) 
--	 wait
	 takeMVar (chopsticks !! ((i+1) `mod` num_phil)) 
	 putStrLn ("Phil #"++(show i)++" eats...")
	 wait
	 putMVar (chopsticks !! i) ()
	 putMVar (chopsticks !! ((i+1) `mod` num_phil)) ()
	 philo chopsticks i

main :: IO ()
main = do 
   num_phil <- getArgs >>= \a-> return (read (head a))
   chopsticks <- mapM (const (newMVar ())) [0.. num_phil-1]
   mapM_ (forkIO . (philo chopsticks)) [0.. num_phil-1]
   block