[Haskell-beginners] STM and IO

[Quentin Moser]

On Thu, 9 Apr 2009 12:03:03 +0200
Quentin Moser <quentin.moser at unifr.ch> wrote:

> Here's an example inspired by the documentation of Control.Concurrent:
> 
> > import Control.Concurrent
> > import Control.Exception (finally)
> >
> > myFork :: IO () -> IO (MVar ())
> > myFork a = do v <- newEmptyMVar
> >               a `finally` (putMVar v ())
> >
> > myWait :: MVar () -> IO ()
> > myWait = readMVar

Oops, my code is completely messed up. Here's a correct version:

> myFork a = do v <- newEmptyMVar
>               forkIO $ a `finally` putMVar v ()
>               return v

> myWait = readMVar >> return ()