As a user who frequently uses ~, but doesn't need the rest of GADTs or TypeFamilies, I'd really like to see a TypeEqualities extension!

Eric

On Fri, Aug 5, 2016 at 3:27 PM, Adam Gundry <adam@well-typed.com> wrote:
On 05/08/16 19:08, David Feuer wrote:
> It seems to me that equality constraints could potentially be supported
> by an implementation with neither GADTs nor type families. Type families
> don't really seem to have much to do with it, and GADTs are strictly
> heavier (GADTs ~= ExistentialQuantification + TypeEquality).
>
> Could we get a separate LANGUAGE pragma just for equality constraints?

I suggested this in #10431 [1], where there is some discussion of the
implications. I still think it is a good idea, and I don't think the
implementation would be very difficult.

All the best,

Adam

[1] https://ghc.haskell.org/trac/ghc/ticket/10431


--
Adam Gundry, Haskell Consultant
Well-Typed LLP, http://www.well-typed.com/
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