[Haskell-beginners] The main thread and waiting for other threads

[Quentin Moser]

As Daniel Fischer already wrote, this is due to an API change in GHC
6.10. But the old exceptions interface is still available as
Control.OldException; you can simply import that instead of
Control.Exception.

On Tue, 12 May 2009 12:27:06 -0400
Thomas Friedrich <info at suud.de> wrote:

> Hi everyone,
> 
> I have a problem with the following example in the Real World Haskell 
> book, which aims to develop a module for controlling different
> threads. See,
> 
> http://book.realworldhaskell.org/read/concurrent-and-multicore-programming.html
> 
> in the chapter "The main thread and waiting for other threads".
> 
> -- file: ch24/NiceFork.hs
> import Control.Concurrent
> import Control.Exception (Exception, try)
> import qualified Data.Map as M
> 
> data ThreadStatus = Running
>                   | Finished         -- terminated normally
>                   | Threw Exception  -- killed by uncaught exception
>                     deriving (Eq, Show)
> 
> -- | Create a new thread manager.
> newManager :: IO ThreadManager
> 
> -- | Create a new managed thread.
> forkManaged :: ThreadManager -> IO () -> IO ThreadId
> 
> -- | Immediately return the status of a managed thread.
> getStatus :: ThreadManager -> ThreadId -> IO (Maybe ThreadStatus)
> 
> -- | Block until a specific managed thread terminates.
> waitFor :: ThreadManager -> ThreadId -> IO (Maybe ThreadStatus)
> 
> -- | Block until all managed threads terminate.
> waitAll :: ThreadManager -> IO ()
> 
> When I run this through ghci I get the following failure:
> 
> [1 of 1] Compiling NiceFork         ( NiceFork.hs, interpreted )
> 
> NiceFork.hs:17:26:
>     Class `Exception' used as a type
>     In the type `Exception'
>     In the data type declaration for `ThreadStatus'
> Failed, modules loaded: none.
> 
> 
> Any idea on how to solve this?  Exception is a class not a type, so
> what to put there instead?
> 
> Cheers,
> Thomas
> 
> 
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