Hi Martin!
On Mon, Mar 16, 2009 at 11:35:22AM +0100, Martin Rubey wrote:
> "Nicolas M. Thiery" <[email protected]> writes:
> > Just a short question: does the interpreter handle transitivity:
> > i.e. if there is a coercion A -> B and one B -> C, then deduce one for
> > A -> C?
>
> I just realized that you probably "really" are asking about how to
> deal with domains that have many representations, bases, etc., like
> symmetric functions.
Definitely! The system should be flexible enough to support this,
among other things.
> I have not come up with a completely satisfying answer yet. One
> possibility is to have a coercion package that performs the
> coercion. A complete (but silly) example is attached.
>
> The problem with this approach is that
>
> MyDom1 has coerce: % -> MyDom2
>
> gives false, because the coerce is not exported by MyDom1, but rather
> by MyCoerce...
> The good thing about this approach is that you can play all tricks
> you like in MyCoerce. For example, you could easily implement
> Dijkstra to find a shortest coercion path. Of course, you could also
> cache this.
>
> Is this what you had in mind?
Yup. That's what's implemented in MuPAD (with some subtleties so as to
scale well to a couple thousand domains/parents, and in particular not
get in the way of the memory management).
The Sage implementation has the same aims.
Cheers,
Nicolas
--
Nicolas M. Thiéry "Isil" <[email protected]>
http://Nicolas.Thiery.name/
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