Phillip, it looks like you're not going to give up. :) I really don't want to accept your proposal into core Python, but I think you ought to be able to implement everything you propose as part of PEAK (or whatever other framework). Therefore, rather than continuing to argue over the merits of your proposal, I'd like to focus on what needs to be done so you can implement it. The basic environment you can assume: an adaptation module according to PEP 246, type declarations according to my latest blog (configurable per module or per class by defining __typecheck__, but defaulting to something conservative that either returns the original object or raises an exception). What do you need then? [My plane is about to leave, gotta run!] -- --Guido van Rossum (home page: http://www.python.org/~guido/)