Re: Type-free Circles and Ellipses [T]

On Fri, 31 Aug 2001 00:51:27 +0100, Owen Rees <owenrees_at_waitrose.deletethis.com> wrote:

>On Thu, 30 Aug 2001 10:05:31 GMT, dmitry_at_elros.cbb-automation.de
>(Dmitry A. Kazakov) wrote:
>
>>If you are arguing against the limitations of the subtype relations
>>usual to the modern OO languages, I am with you. There is nothing
>>fundamental that requires the subtype relation be a tree.
>
>In most of the useful theory that I have seen, the subtype relation is
>described as forming a lattice. Of course, for that to work, you have
>to be able to think about types that have never been written down, but
>which are derived as meets or joins of other types. Of the types you
>start with, some are written down explicitly, and others are inferred
>from various language constructs, and the types used in them.

Nice.

>In the language we invented when I was working on the ANSA
>computational model, expressions and variables had different kinds of
>types. The two kinds of types had conformance relations which each
>formed semi-lattices, but opposite ways up. The other thing we did was
>to ban the use of the word 'subtype' in our reports and discussions;
>we did that because the emotive connotations, the confusion with
>inheritance and the potential to be confused about which way was 'up'
>made it a liability.
>
>Ever since then I have found the type systems in languages that
>purport to be OO deeply unsatisfying.

1. Is there some report available?
2. The confusion between inheritance and your x-types, what it was. Do you mean that an x-type does not always inherit?
3. Were supertypes allowed?
4. Did you played with multiple dispatch on such a loose type structure?

Regards,
Dmitry Kazakov Received on Fri Aug 31 2001 - 17:50:39 CEST