Thank you very much for your answers. As I said in my post I knew the synopsis,
but I hoped to have something more precise. I will explore it again by using
Timoty roadmap
On 02/05/2010 01:59 AM, Darren Duncan wrote:
G. Castagna: Covariance and contravariance: conflict without a cause. ACM
Transactions on Programming Languages and Systems, vol. 17, n. 3, pag.
431-447, 1995.
Is there an electronic copy of this that you can link to?
Ah, spoke too soon. An electronic copy is linked to from one of the other
sites you gave, at http://www.pps.jussieu.fr/~gc/selected.en.html ; the PDF
version is at http://www.pps.jussieu.fr/~gc/papers/toplas95.pdf .
Well, glad you found the "contravariance" paper. For what concerns CDuce, the
language is included in most linux distributions (Ubuntu Debian, Fedora,
Mandriva, at least). For the type system, while I think that the
"contravariance" paper is rather accessible (I hope), the most accessible
presentation for CDuce types is probably the joint keynote talk I gave at PPDP
and ICALP, that can retrieved here
http://www.pps.jussieu.fr/~gc/papers/icalp-ppdp05.pdf
while it is a little bit technical, you can use the covariance paper as a key of
reading: the type of an overloaded function (set of arrows) is there an
intersection of the arrows.
And by "union types", I mean both that you can say "Dog | Cat" (syntax?) to
allow either Dog or Cat values, and also that Perl 6 roles effectively
declare union types but that the members add themselves to the union rather
than the union itself declaring what it ranges over; in the latter case, the
union type is "every value that does this role".
Well union for must are just ... unions. So the type Int | Bool | "Dog" is
intuitively the set {"Dog", true, false, 1, 2, 3, ....}. That is, both
enmuerated sets, and set theoretic unions.
Finally, if you use the CDuce type theory for Perl 6 you obtain for free pattern
matching for XML values, if you are interested in it (probably it will require a
little effort to make the syntax compatible with perl regexps).
I see I'm going out of the scope of this list. I apologize for spamming, but
please continue to post here or send me by PM every information about Perls 6 types.
---Beppe---
