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

so a term of type a==b lets you locally introduce the hypothesis that a~b in the local types? (just making sure i understand this). whats use case for the type level boolean equality? Naively, it seems like that could be derived from a typelevel " Maybe (a==b)'' plus a type level version of the "maybe" combinator On Sun, Sep 29, 2013 at 12:10 AM, Richard Eisenberg wrote:

-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:

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On Sat, Sep 28, 2013 at 6:57 PM, Edward Kmett wrote:

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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/fb47f8368ad3d40fdd79bdeec334c...

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Thoughts?

Normally, I'd let this run the usual 2 week course, but we're getting

down

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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 _______________________________________________ Libraries mailing list Libraries@haskell.org http://www.haskell.org/mailman/listinfo/libraries

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