>I recently upgraded to ghc 7.0.2 from 6.12.3, along with the Haskell platform, >and noticed that the following code no longer works as expected: > >waitFor tvar = atomically $ do > count <- readTVar tvar > check (count == 0) > >worker tchan tvar = loop > where loop = do > putStrLn "checking" > finished <- atomically $ isEmptyTChan tchan > threadDelay 50000 > if finished > then atomically $ do val <- readTVar tvar > writeTVar tvar $ (subtract 1) val > else (atomically $ readTChan tchan) >> loop > >test = do > tchan <- newTChanIO > pure $ forM_ [1..5] $ writeTChan tchan -- THIS LINE > tvar <- newTVarIO 1 > forkIO $ worker tchan tvar > waitFor tvar > putStrLn "DONE"
You did not include your imports, but I assume that's Control.Applicative.pure. If so, that line should never do anything. pure for IO is the same as return - you are never running the STM action that line calculates. It's the same as if you had written >test = do > tchan <- newTChanIO > let neverGetsUsed = forM_ [1..5] $ writeTChan tchan -- THIS LINE > tvar <- newTVarIO 1 > forkIO $ worker tchan tvar > waitFor tvar > putStrLn "DONE" Brandon _______________________________________________ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe