On Sat, Sep 17, 2005 at 12:36:06PM -0700, Jason Dagit wrote:
On Sep 17, 2005, at 1:43 AM, Bulat Ziganshin wrote:
about making Bool a class - it is the same issue as making head/map/... belonging to some Collection class. we need to change standard Prelude or add to Haskell "supertyping" mechanism, proposed by John Meacham, as i remember
A link to supertyping can be found here: http://repetae.net/john/recent/out/supertyping.html
After reading that, I wonder why it's not implemented. It seems like a wonderfully useful idea. I view it as a way to add things back to the language which should have been there to begin with, but which the language designers left out for various reasons (such as lack of time, interest or possibly even oversight).
I actually have some misgivings about the design I stated there and would have some tweaks I would like to do before it was actually implemented, but I definitly think we need more flexible ways to deal with class hierachies (in some form). my main concern is that class Eq a => Ord a where class Ord a <= Eq a where are not fully symmetric. the second lets you just declare things as Ord without worrying about Eq, the first doesn't. I think these issues can be worked out once a concrete implementation is being worked on, which I hope to do for jhc. John -- John Meacham - ⑆repetae.net⑆john⑈