module Main where

import Concurrent
import System(getArgs)
import Random(randomRIO)

philo :: [MVar ()] -> Int-> IO ()
philo chopsticks i = 
   let num_phil = length (chopsticks) 
   in do putStrLn ("Phil #"++(show i)++" thinks...")
         randomRIO (500,2000) >>= threadDelay
         takeMVar (chopsticks !! i)
         takeMVar (chopsticks !! ((i+1) `mod` num_phil))
         putStrLn ("Phil #"++(show i)++" eats...")         
         randomRIO (500,2000) >>= threadDelay
         putMVar (chopsticks !! i) ()
         putMVar (chopsticks !! ((i+1) `mod` num_phil)) ()
         philo chopsticks i

main :: IO ()
main = do num <- getArgs >>= \a-> return (read (head a))
          chopsticks <- sequence 
                         (take num (repeat (newMVar ())))
          mapM_ (forkIO . (philo chopsticks)) [0.. num-1]
          block

block :: IO ()
block = newEmptyMVar >>= takeMVar