I've started work on a module to replace Control.Exception by wrapping all the original Control.Exception functions in more general monadic functions and using two type classes as follows: class MonadIO m => MonadException m where catch :: m a -> (Exception -> m a) -> m a catchDyn :: Typeable exception => m a -> (exception -> m a) -> m a catchJust :: (Exception -> Maybe b) -> m a -> (b -> m a) -> m a try :: m a -> m (Either Exception a) tryJust :: (Exception -> Maybe b) -> m a -> m (Either b a) and class MonadIO m => MonadIOU m where getUnliftIO :: m (m a -> IO a) All the other functions can be implemented just using MonadIO or MonadIOU or MonadException in place of IO (depending on the function eg bracket needs MonadIOU) - just in case anyone is interested. As far as I can tell this seems to be the one and only way to do it with the minimal sized classes but I'd be interested if anyone has found a better way. Regards, Brian.