Concurrent prime sieve translated from Go (http://play.golang.org/p/9U22NfrXeq)

concurrent_sieve.hs

-- Compile with `ghc -threaded -with-rtsopts=-N concurrent_sieve.hs`

import Control.Concurrent
import Control.Monad

import System.Environment

generate :: MVar Int -> IO ()
generate mOut = mapM_ (putMVar mOut) [2..]

primeFilter :: MVar Int -> MVar Int -> Int -> IO ()
primeFilter mIn mOut prime = forever $
    takeMVar mIn >>= \i -> when (i `mod` prime /= 0) (putMVar mOut i)

main = do numArg:_ <- getArgs
          m1 <- newEmptyMVar
          forkIO $ generate m1
          ms <- replicateM (read numArg) newEmptyMVar
          foldM_ linkFilter m1 ms

linkFilter :: MVar Int -> MVar Int -> IO (MVar Int)
linkFilter mIn mOut = do prime <- takeMVar mIn
                         putStrLn $ show prime
                         forkIO $ primeFilter mIn mOut prime
                         return mOut