On 8/10/05, TSa <[EMAIL PROTECTED]> wrote:
> HaloO,
>
> Luke Palmer wrote:
> > On 8/9/05, Larry Wall <[EMAIL PROTECTED]> wrote:
> >
> >>So why not just use "describes"? Then maybe Object.isa(Foo) delegates
> >>to $obj.meta.describes(Foo).
> >
> >
> > Hmm. We have a similar problem with the new class-set notation.
> > These two things:
>
> Did I miss something? What is the class-set notation?
A new development in perl 6 land that will make some folks very happy.
There is now a Set role. Among its operations are (including
parentheses):
(+) Union
(*) Intersection
(-) Difference
(<=) Subset
(<) Proper subset
(>=) Superset
(>) Proper superset
(in) Element
(=) Set equality
I believe the unicode variants are also allowed.
And now we're doing away with junctive types in favor of set types.
This was mostly because:
(A|B) (<=) A
Expands to
A (<=) A || B (<=) A
Which is true. Such a type can not exist, lest every type be equal to
every other type.
So now Type does Set, so we have:
A (+) B # type representing a value that is either A or B
A (*) B # type representing a value that is both A and B
A (-) B # type representing a value that is A but not B
etc.
So types are merely sets of (hypothetical, eventual) instances,
together with a few operations to make introspection etc. easier.
You might even get Piers's all-instance introspection by Foo.elements.
That's not a guarantee though.
> > $a.does(Foo);
> > Bar.does(Foo);
> >
> > Mean two different things:
>
> Really?
Yep:
$a.does(Foo) $a (in) Foo
Bar.does(Foo) Bar (<=) Foo
Assuming that $a is not a type.
If there is any extra structure beyond set structure that we need in a
type lattice, I think it's your job to tell us what that is.
Luke
