Re: How do I create dynamic exceptions

On Tue, Jul 22, 2003 at 02:59:12PM +0100, Bayley, Alistair wrote:

...

handler :: Dynamic -> IO () handler e = do case (fromDynamic e) of Nothing -> putStrLn ("dynamic cast failed") Just (MkExc n s) -> putStrLn ("exception: " ++ (show n) ++ " " ++ s)

...

main :: IO () main = catchDyn temp handler

You're catching a Dynamic wrapped as a Dynamic (catchDyn already does fromDynamic, as indicated by its type). Change the handler to

handler :: MyException -> IO () handler (MkExc n s) = putStrLn ("exception: " ++ (show n) ++ " " ++ s)

any other dynamic exception fails through to the top level.