Hi Stephen,
I wasn't aware of Data.Dynamic.
I tried:

viewEvent :: Dynamic -> IO ()
viewEvent event = do
   case fromDynamic event of
        Nothing -> return ()
        Just (Message s) -> putStrLn $ show s

But still got the same error (Ambiguous type variable `t0' in the constraint: (Typeable t0) arising from a use of `fromDynamic')...

Best,
Corentin

On Mon, Sep 10, 2012 at 11:33 PM, Stephen Tetley <stephen.tetley@gmail.com> wrote:

Whilst dynamic typing isn't idiomatic for Haskell, it seems like
you've decided you want it. So why not use Data.Dynamic rather than
roll you're own dynamic typing with Typeable?