Re: [Haskell-cafe] Mixing IO and STM

29 Dec 2005


      On 12/29/05, Quan Ta  wrote:
...
Hello folks,
Newbie question: how can I do something like the following? mixing IO and
STM.
module Test where
import System.Random
 import Control.Concurrent
import Control.Concurrent.STM
test_Cubby =
  do
Change this:
...
tv <- newTVar 0
To this:
...
tv <- atomically (newTVar 0)

...
forkIO (producer tv) >> (consumer tv)
  where
     producer tv = do r <- randomRIO (1,10)
                     atomically (do { v <- readTVar tv
                                    ; writeTVar tv (v+r)
                                    })
                      print ("insert " ++ show r)
                     producer tv
                     return ()
    consumer tv = do r <- randomRIO (1,10)
                      atomically (do { v <- readTVar tv
                                    ; if (v < r) then retry
                                      else writeTVar tv
(v-r)
                                    })
                      print ("consume " ++ show r)
                     consumer tv
                     return ()
--
Friendly,
  Lemmih