On Tue, Jun 15, 2004 at 06:29:59PM -0400, S. Alexander Jacobson wrote:
> I'd like a function that blocks until data is
> available on one of two channels and then returns
> that data wrapped in an Either. Here is my naive
> implementation:
>
> readEitherChan::Chan a -> Chan b -> Either a b
> readEitherChan a b =
> do
> var <- newEmptyMVar
> forkIO (readChan a >>= putMVar var . Left)
> forkIO (readChan b >>= putMVar var . Right)
> val <- readMVar
> return val
>
> eitherChan a b left right = readEitherChan a b >>= either left right
>
> But creating an MVar and starting two threads
> feels like a lot of overhead for a simple
> operation.
You can also loose some elements from both channels. I think it would be
safer to create once new Chan (Either a b), and then read from it.
createEitherChan :: Chan a -> Chan b -> IO (Chan (Either a b))
createEitherChan a b = do
ab <- newChan
forkIO (sequence_ (repeat (readChan a >>= writeChan ab . Left)))
forkIO (sequence_ (repeat (readChan b >>= writeChan ab . Right)))
return ab
Best regards,
Tom
--
.signature: Too many levels of symbolic links
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