[Haskell-cafe] Eq Type Class: Overloading (==)
john at repetae.net
Sun Sep 18 20:28:22 EDT 2005
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:
> 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 Meacham - ⑆repetae.net⑆john⑈
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