MVar's met STM

Meld je aan om je oplossing in te dienen en feedback te krijgen.

import Control.Concurrent.STM (STM, TVar, newTVar, readTVar, writeTVar, retry, atomically)
import Control.Concurrent (threadDelay, forkIO)
import Prelude hiding (read)


newtype STMMVAR a = STMMVAR (TVar (Maybe a))

newEmptySTMMVAR :: STM (STMMVAR a)
newEmptySTMMVAR = undefined

takeSTMMVAR :: STMMVAR a -> STM a
takeSTMMVAR (STMMVAR t) = undefined

putSTMMVAR :: STMMVAR a -> a -> STM ()
putSTMMVAR (STMMVAR t) a = undefined


write :: STMMVAR String -> STMMVAR String -> IO ()
write ta tb = do threadDelay 1000000
                 atomically $ do putSTMMVAR ta "Hello"
                                 putSTMMVAR tb "World"
                                 return ()

read :: STMMVAR String -> STMMVAR String -> IO (String, String)
read ta tb = atomically $ do b <- takeSTMMVAR tb
                             a <- takeSTMMVAR ta
                             return (a,b)

main :: IO ()
main = do ta <- atomically newEmptySTMMVAR
          tb <- atomically newEmptySTMMVAR
          _  <- forkIO $ write ta tb
          x  <- read ta tb
          putStrLn $ show x