try2.hs

import Control.Monad
import Control.Concurrent.MVar
import Control.Concurrent
import Text.Printf
import System.Random

fuzz :: IO ()
fuzz = do
  seconds <- getStdRandom random :: IO Double
  threadDelay $ round (realToFrac (1000000 * seconds))

counterManager :: MVar Integer -> Chan Integer -> Chan [String] -> IO ()
counterManager counter counterCh printerCh = forever $ do
  fuzz
  incrementBy <- readChan counterCh
  fuzz
  newCount <- modifyMVar counter (\i -> return (i + 1, i + 1))
  fuzz
  writeChan printerCh [printf "The count is %d" newCount,
                       "---------------"]
  fuzz

printerManager :: Chan [String] -> IO ()
printerManager ch = forever $ do
  fuzz
  rows <- readChan ch
  fuzz
  mapM_ putStrLn rows
  fuzz

main :: IO ()
main = do
  counter <- newMVar 0
  counterCh <- newChan
  printerCh <- newChan
  forkIO $ counterManager counter counterCh printerCh
  forkIO $ printerManager printerCh
  writeChan printerCh ["Starting up"]
  replicateM_ 10 (writeChan counterCh 1)
  -- join counterCh
  writeChan printerCh ["Finishing up"]
  -- join printerCh
  threadDelay $ 20 * 1000000