[David Abrahams]

I don't know how these things usually work, but isn't it a bit early for that? I would like to have some discussion about multiple dispatch (and especially matching criteria) before investing in a formal proposal. That's what my earlier posting which got banished to the types-sig was trying to do. Getting a feel for what people are thinking about this, and getting feedback from those with lots more experience than I in matters Pythonic is important to me.

I'm interested in multiple dispatch [but have limited band-width], once I have even written a pure Python implementation of it (only on classes). It's quite expressive for some designs. But: [- Jython too internally uses a kind of multiple-dispatch in order to dispatch to overloaded Java methods. But such a mechanims is really quite a limited beasts wrt to adding multiple-dispatch to Python in general. ] - I'm not sure is that much Pythonic or easy to grasp, one remark that I have read sometimes is that with multimethods the program logic is easely scattered in many places with so-to-say non-local effects. - It is yet another paradigm that should be integrated with the rest of Python. For example how does it interact with the current single-dispatched methods, does it? [It is not just a theoretical question, it influences whether this can be used to model e.g. the dispatch of Jython for overloaded Java methods or not, simplifying the picture or adding confusion] - Syntax and semantics: in Python definitions are assignments. Now one needs at least a (maybe implicit) define generic function and an add method to generic function. (Should def be abused?) - Should all function (methods) definitions define generic function methods under the hood. - Do we dispatch on only foo.__class__ or do we want to dispatch on protocols/interfaces/categories, now at the moment these are not first-class in Python. - How do we solve dispatch ambiguities, the more predictable and uncomplicated the more Pythonic. - Sometimes it is useful to substitute functions and methods with wrapped re-editions, the equivalent for multi-method are at least before,after,around combinators, I think they are useful, but make the picture more complex. So the question is more what is the most pythonic way we can find to add multiple dispatch, then maybe it is Pythonic enough or not. [It seems a SIG task but I have not really written that word <.5 wink>] Related: Smallscript, CLOS, Dylan, various overloading flavors Smallscript is interesting because it adds multiple dispatch to the single-dispatch semantics of Smalltalk, so it's very overlapping with our case, OTOH I have not played with it and I don't know the details of the actual semantics, [and in general it gives a PL/I-esque impression, at least from far away]. regards.