[Haskell-cafe] Mixing IO and STM

[Lemmih]

On 12/29/05, Quan Ta <quancta at gmail.com> 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