哲学家晚餐问题的Haskell求解

最近上课讲到，哲学家晚餐死锁避免，然后发现张凇这里的代码是空白，0Bite,以为是我自己的下载错了，点开第一版源代码，发现：
也是空白，然后第二版的代码好像也没找了，然后找到了神网站http://rosettacode.org/wiki/Rosetta_Code

哲学家晚餐问题全家桶


import Control.Monad
import Control.Concurrent
import Control.Concurrent.STM
import System.Random-- TMVars are transactional references. They can only be used in transactional actions.
-- They are either empty or contain one value. Taking an empty reference fails and
-- putting a value in a full reference fails. A transactional action only succeeds
-- when all the component actions succeed, else it rolls back and retries until it
-- succeeds.
-- The Int is just for display purposes.
type Fork = TMVar IntnewFork :: Int -> IO Fork
newFork i = newTMVarIO i-- The basic transactional operations on forks
takeFork :: Fork -> STM Int
takeFork fork = takeTMVar forkreleaseFork :: Int -> Fork -> STM ()
releaseFork i fork = putTMVar fork itype Name = StringrunPhilosopher :: Name -> (Fork, Fork) -> IO ()
runPhilosopher name (left, right) = forever $ doputStrLn (name ++ " is hungry.")-- Run the transactional action atomically.-- The type system ensures this is the only way to run transactional actions.(leftNum, rightNum) <- atomically $ doleftNum <- takeFork leftrightNum <- takeFork rightreturn (leftNum, rightNum)putStrLn (name ++ " got forks " ++ show leftNum ++ " and " ++ show rightNum ++ " and is now eating.")delay <- randomRIO (1,10)threadDelay (delay * 1000000) -- 1, 10 seconds. threadDelay uses nanoseconds.putStrLn (name ++ " is done eating. Going back to thinking.")atomically $ doreleaseFork leftNum leftreleaseFork rightNum rightdelay <- randomRIO (1, 10)threadDelay (delay * 1000000)philosophers :: [String]
philosophers = ["Aristotle", "Kant", "Spinoza", "Marx", "Russel"]main = doforks <- mapM newFork [1..5]let namedPhilosophers  = map runPhilosopher philosophersforkPairs          = zip forks (tail . cycle $ forks)philosophersWithForks = zipWith ($) namedPhilosophers forkPairsputStrLn "Running the philosophers. Press enter to quit."mapM_ forkIO philosophersWithForks-- All threads exit when the main thread exits.getLine

然后网站的Haskell上述源代码好像出了点问题，

好吧，其实我也很好奇这个乱码部分的原因是什么，求解。
然后，换个写法吧。

import Control.Concurrent
import Control.Concurrent.STM
import Control.Monad
import System.Randomtype Fork = TVar Bool
type StringBuffer = TChan StringphilosopherNames :: [String]
philosopherNames = map show ([1..] :: [Int])logThinking :: String -> StringBuffer -> STM ()
logThinking name buffer = writeTChan buffer $ name ++ " is thinking..."logEating :: String -> StringBuffer -> STM ()
logEating name buffer = writeTChan buffer $ name ++ " is eating..."firstLogEntry :: StringBuffer -> STM String
firstLogEntry buffer = do empty <- isEmptyTChan bufferif empty then retryelse readTChan buffertakeForks :: Fork -> Fork -> STM ()
takeForks left right = do leftUsed <- readTVar leftrightUsed <- readTVar rightif leftUsed || rightUsedthen retryelse do writeTVar left TruewriteTVar right TrueputForks :: Fork -> Fork -> STM ()
putForks left right = do writeTVar left FalsewriteTVar right Falsephilosopher :: String -> StringBuffer -> Fork -> Fork -> IO ()
philosopher name out left right = do atomically $ logThinking name outrandomDelayatomically $ takeForks left rightatomically $ logEating name outrandomDelayatomically $ putForks left rightrandomDelay :: IO ()
randomDelay = do delay <- getStdRandom(randomR (1,3))threadDelay (delay * 1000000)main :: IO ()
main = do let n = 8forks <- replicateM n $ newTVarIO Falsebuffer <- newTChanIOforM_ [0 .. n - 1] $ \i ->do let left = forks !! iright = forks !! ((i + 1) `mod` n)name = philosopherNames !! iforkIO $ forever $ philosopher name buffer left rightforever $ do str <- atomically $ firstLogEntry bufferputStrLn str

老铁，没毛病，(-_-#.

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