[Aldor-l] [open-axiom-devel] coercion problem

[Martin Rubey]

Ralf Hemmecke <ralf at hemmecke.de> writes:

> > Now, I would like that for domains of the same category, say
> > UnivariatePolynomialCategory, that differ only in the representation of
> > their elements, say sparse or dense, we would have
> 
> > A has CoercibleTo B and B has CoercibleTo A
> 
> OK, let's say I take AbelianMonoid as a category. For A, I take Integer and
> for B, I take String (just let's suppose 0: String is the empty string and +:
> (String, String) -> String is concatenation.

One can hardly say that these two domains differ only in the representation of
their elements.

So, I should have been more precise:

There are categories (like for example UPOLYC), where it makes sense to have
for any two domains A and B of that category

A has CoercibleTo B and B has CoercibleTo A.

However, it seems that this cannot be expressed in SPAD or Aldor.

Somehow, it might be nice to have the possibility to say

with CoercibleTo B where B has SomeCategory


Martin