"Bill Page" <[EMAIL PROTECTED]> writes:

> On Tue, Dec 9, 2008 at 6:35 PM, Martin Rubey wrote:
> >
> > I see that extend is nice, but actually, within FriCAS I don't see whether
> > it's such a big issue?  Maybe for the coercion definitions, but actually,
> > that's one place where I think that Aldor is missing functionality, i.e.,
> > allow something like
> >
> >    forall A if A has MyCat then CoercibleTo A
> >
> > or perhaps
> >
> >    CoercibleTo A where A has MyCat.
> >
> 
> I presume that you mean that one might write this in the context of
> some domain, say B.
> 
> Isn't this essentially what one might do in defining a package? E.g.
> 
>   MyCoercePac(A:MyCat,X:CatOf(B)): CoercibleTo(A)
>     == add
>        coerce(x:X):A == ...
> 
> At least in the interpreter if 'MyCoercePac' is exposed than the
> interpreter can expect to find a function 'coerce' for all domains A
> in MyCat.

But A has CoercibleTo B will be false...

(we had this discussion very recently)

Martin


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