Producer-Consumer by STM

pc.hs

import Control.Concurrent(forkIO,threadDelay)
import qualified Control.Concurrent.STM.TChan as TChan
import qualified Control.Monad.STM as STM

main = do
  rp <- TChan.newTChanIO
  pc <- TChan.newTChanIO
  forkIO $ produce pc
  forkIO $ produce pc
  forkIO $ produce pc
  forkIO $ consume 0 rp pc
  forkIO $ consume 1 rp pc
  forkIO $ consume 2 rp pc
  forkIO $ consume 3 rp pc
  forkIO $ consume 4 rp pc
  forkIO $ consume 5 rp pc
  forkIO $ consume 6 rp pc
  forkIO $ consume 7 rp pc
  forkIO $ consume 8 rp pc
  forkIO $ consume 9 rp pc
  report rp
    
produce :: TChan.TChan Int -> IO()
produce c = loop 0
  where
    loop n = do
      STM.atomically $ TChan.writeTChan c n 
      threadDelay 10
      loop $ n+1
      
consume :: Int -> TChan.TChan String -> TChan.TChan Int -> IO()
consume id rp pc = loop
  where
    loop = do
      n <- STM.atomically $ TChan.readTChan pc
      STM.atomically $ TChan.writeTChan rp $ "consume:" ++ (show id) ++ ":" ++ (show n)
      threadDelay 100
      loop

report :: TChan.TChan String -> IO()
report c = loop
  where
    loop = do
      msg <- STM.atomically $ TChan.readTChan c
      putStrLn msg
      loop