GHC 8.0 feature freeze imminent

Ben Gamari ben at
Mon Dec 14 19:32:59 UTC 2015

Ryan Scott < at> writes:

> One thing I definitely want to get in before the 8.0 release is:
> * A fix for Trac #10716 [1] (adding strictness metadata to GHC
> generics). This feels like a natural counterpart for Trac #10697 [2]
> (reworking strictness information to Template Haskell), which
> currently has a Phab Diff in review [3]. I'd like for these to be
> released at the same time so that I can use Template Haskell to
> backport the machinery in generic-deriving [4]. In addition, I
> realized that my encoding of selector metadata is not very extensible
> at the moment, and this would give me a good excuse to fix it.
I've added these to "likely to land" list on the release status page.

> Some things that I probably won't get in time for 8.0:
> * Automatic derivation of Bifunctor/Bifoldable/Bitraversable, and of
> Eq1/Eq2/Ord1/Ord2/Read1/Read2/Show1/Show2. These would require
> resolving Trac #10448 [5] and #11135 [6] first, which might need more
> discussion. Not only that, but I still need to write up a proposal for
> how each of these classes would be derived, and there would need to be
> additional discussion on those points... All in all, it doesn't sound
> like something I could do in two weeks :)
Indeed this sounds like it might be a bit of a stretch.

> * Making Generic1 kind-polymorphic, Trac #10604 [7]. The first step to
> achieving this was done recently [8], but unfortunately, I wasn't able
> to make the actual datatypes in GHC.Generics kind-polymorphic for
> unknown reasons (I'd still like to talk to Richard Eisenberg about
> this at some point). Not only that, but I'm not sure what the
> implications of making Generic1 poly-kinded would be yet. I'd like to
> talk to Andres Löh about this.
Good luck and let me know if I can be of assistance!


- Ben

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