[Proposal] Renaming (:=:) to (==)

[Erik Hesselink]

I agree. I would expect (==) to be something like:

type family (x :: k) == (y :: k) :: Bool where
  a == a = True
  a == b = False

As for the equality witness type, I think there's nothing wrong with
(:=:). This way, it can also have the same name as the constructor,
which still has to start with a colon, as far as I know. (:~:) would
also be fine by me, but I don't think a name without colons is
desirable.

Erik

On Sun, Sep 29, 2013 at 2:33 PM, Roman Cheplyaka <roma at ro-che.info> wrote:
> I agree with Richard here — this overloading of == doesn't seem
> intuitive to me. Using it for type-level boolean equality would be much
> more natural.
>
> That said, :=: could probably benefit from the relaxed rules for type
> operators; I just don't think == is a good choice.
>
> Roman
>
> * Richard Eisenberg <eir at cis.upenn.edu> [2013-09-29 00:10:46-0400]
>> -1 from me.
>>
>> Shachaf stated my argument correctly -- I think that the (:=:) operator means something quite different from the term-level (==) operator, and the name should reflect this. I do like thinking about a better name, though, and I'm happy enough if I'm outvoted here.
>>
>> Richard
>>
>> On Sep 28, 2013, at 10:08 PM, Shachaf Ben-Kiki wrote:
>>
>> > On Sat, Sep 28, 2013 at 6:57 PM, Edward Kmett <ekmett at gmail.com> wrote:
>> >> As part of the discussion about Typeable, GHC 7.8 is going to include a
>> >> Data.Type.Equality module that provides a polykinded type equality data
>> >> type.
>> >>
>> >> I'd like to propose that we rename this type to (==) rather than the (:=:)
>> >> it was developed under.
>> >>
>> >> We are already using (+), (-), (*), etc. at the type level in type-nats, so
>> >> it would seem to fit the surrounding convention.
>> >>
>> >> I've done the work of preparing a patch, visible here:
>> >>
>> >> https://github.com/ekmett/packages-base/commit/fb47f8368ad3d40fdd79bdeec334c0554fb17110
>> >>
>> >> Thoughts?
>> >>
>> >> Normally, I'd let this run the usual 2 week course, but we're getting down
>> >> to the wire for 7.8's release. Once 7.8 ships, we'd basically be stuck with
>> >> the current name forever.
>> >>
>> >> Discussion Period: 1 week
>> >>
>> >> -Edward Kmett
>> >>
>> >
>> > +1. For what it's worth, I suggested that name before, and Richard
>> > Eisenberg suggested that == should be for type-level Boolean equality:
>> > <http://markmail.org/message/3yifytgt2k3cfwws>. I'm not convinced,
>> > though -- this seems fundamental enough to deserve the simplest name
>> > possible.
>> >
>> > (I'm using that link because the haskell.org mailing list archive
>> > seems to be gone... Hopefully that comes back, eventually.)
>> >
>> >    Shachaf
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