Can we offer ~ without GADTs or type families?

Adam Gundry adam at
Fri Aug 5 19:27:49 UTC 2016

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 Gundry, Haskell Consultant
Well-Typed LLP,

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