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

[Rafael Gustavo da Cunha Pereira Pinto]

The problem is that Exception is a class. You should use SomeException,
which is a type!




On Tue, May 12, 2009 at 13:27, 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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>



-- 
Rafael Gustavo da Cunha Pereira Pinto
Electronic Engineer, MSc.
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