[Haskell-cafe] Re: IO exception not being caught

16 Nov 2005

      I fixed up my timeout function to look like this:

timeout :: forall a.Show a => Int -> IO a -> IO a
timeout secs fun =
     mdo mvar <- newEmptyMVar
         tid1 <- forkIO $ do result <- try fun
                             putMVar mvar $
                                     either (Left . show) (Right . id)
                                            result
                             killThread tid2
         tid2 <- forkIO $ do threadDelay (secs * 1000000)
                             putMVar mvar (Left "timeout")
                             killThread tid1
         maybeResult <- takeMVar mvar
         case maybeResult of
           Right a -> return a
           Left b -> fail b

But the IOError is still not being caught by liftIOTrap.

Any clues?

	Thanks, Joel

On Nov 16, 2005, at 1:27 PM, Joel Reymont wrote:
...
Folks,
I have a problem catching my IO exception with the code below. The  
intent is to catch either the IO exception from connectTo  
(connection refused, etc.) or the timeout.
type EngineState = ErrorT String (StateT World IO)
fromIOError err = ioeGetErrorString err
liftIOTrap :: IO a -> EngineState a
liftIOTrap io =
    do mx <- liftIO (do x <- io
                        return (return x)
                                   `catchError`
                                   (\e -> return (throwError
                                                  (fromIOError e))))
       mx
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