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

[Richard Eisenberg]

Thanks for pointing this out, Edward. I think consistency within the type level is more important than consistency between the type level and the term level. So, if we settle on a convention that a symbol ending in `?` means Boolean-valued and other symbols mean constraints, I'm all for making the change to (==).

I'm not aware of a wide poll on the names in TypeLits, so we shouldn't necessarily just follow that lead. That said, the above proposal about `?` seems sensible to me. If we decide to do this, we should find somewhere (where??) to articulate this.

Richard 

On Oct 2, 2013, at 9:28 PM, Edward Kmett <ekmett at gmail.com> wrote:

> GHC.TypeLits code looks to be using (<=?) as the boolean valued version of the predicate and (<=) for the assertion.
> 
> This points to a coming disagreement over style across the different parts of GHC itself, if we're saying that the principle reason for not using (==) is that we want it to be the boolean valued version.
> 
> -Edward
> 
> 
> On Mon, Sep 30, 2013 at 4:03 PM, Carter Schonwald <carter.schonwald at gmail.com> wrote:
> Agreed. 
> 
> 
> On Monday, September 30, 2013, Edward A Kmett wrote:
> I think if someone went through the effort of writing a patch so you could at least introduce local operator names with an explicit forall, like with ScopedTypeVariables and the proposed explicit type applications then it'd probably be accepted.
> 
> Sent from my iPhone
> 
> On Sep 30, 2013, at 2:25 PM, Conal Elliott <conal at conal.net> wrote:
> 
>> -1.
>> 
>> I'm hoping we don't get more deeply invested in the syntactic change in GHC 7.6 that removed the possibility of symbolic type variables ("~>", "*", "+", etc). I had a new job and wasn't paying attention when SPJ polled the community. From my perspective, the loss has much greater scope than the gain for type level naturals. I'd like to keep the door open to the possibility of bringing back the old notation with the help of a language pragma. It would take a few of us to draft a proposal addressing details.
>> 
>> Not at all meaning to start a syntax debate on this thread. Just an explanation of my -1 for the topic at hand.
>> 
>> - Conal
>> 
>> -- Conal
>> 
>> 
>> On Sat, Sep 28, 2013 at 9:57 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
>> 
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