On Thu, Oct 9, 2008 at 18:10, Arnar Birgisson
But I did write a concurrent prime sieve with it:
I did the same, with the one-place-buffers (the MVars implemented over STM). Be warned that there is no stop condition, this just keeps printing primes forever.
Please forgive me for reposting, but the last one exited quite prematurely :) module Main where import Control.Concurrent (forkIO) import Control.Concurrent.STM import System (getArgs) -- MVars from the STM paper type MVar a = TVar (Maybe a) newEmptyMVar :: STM (MVar a) newEmptyMVar = newTVar Nothing takeMVar :: MVar a -> STM a takeMVar mv = do v <- readTVar mv case v of Nothing -> retry Just val -> do writeTVar mv Nothing return val putMVar :: MVar a -> a -> STM () putMVar mv val = do v <- readTVar mv case v of Nothing -> writeTVar mv (Just val) Just _ -> retry -- Sieve forever a = do a; forever a pfilter :: Int -> MVar Int -> MVar Int -> IO () pfilter p in_ out = forever $ do atomically $ do v <- takeMVar in_ if v `mod` p /= 0 then putMVar out v else return () sieve :: MVar Int -> MVar Int -> IO () sieve in_ out = do p <- atomically $ takeMVar in_ atomically $ putMVar out p ch <- atomically $ newEmptyMVar forkIO $ pfilter p in_ ch sieve ch out feeder :: MVar Int -> IO () feeder out = feed' 2 where feed' i = do atomically $ putMVar out i feed' (i+1) printer :: MVar () -> MVar Int -> Int -> IO () printer stop in_ max = do v <- atomically $ takeMVar in_ putStrLn $ show v if v > max then atomically $ putMVar stop () else printer stop in_ max main :: IO () main = do max:_ <- getArgs in_ <- atomically newEmptyMVar out <- atomically newEmptyMVar stop <- atomically newEmptyMVar forkIO $ feeder in_ forkIO $ printer stop out (read max) forkIO $ sieve in_ out atomically $ takeMVar stop return ()