Re: [ghc-steering-committee] Proposal #209: Levity polymorphic lift. Recommendation: accept

I believe you're thinking of https://github.com/ghc-proposals/ghc-proposals/pull/175. The PR has been marked accepted, but it seems it didn't get merged. On Mon, Mar 4, 2019, at 22:16, Richard Eisenberg wrote:

I recall a discussion in another proposal about the Lift class and removing the lift function. This was for a good reason (I think it stopped silent, terrible breakage). Does anyone remember where that conversation took place? A quick search didn't find an accepted proposal about the Lift class.

Thanks, Richard

...

On Mar 2, 2019, at 4:41 PM, Eric Seidel wrote:

Hi everyone,

This proposal[1] makes the `lift` and `liftTyped` methods of the `Lift` class levity-polymorphic, which allows us to write proper `Lift` instances for unlifted types. It would also allow GHC to remove the special logic that currently supports lifting records with unlifted fields.

The main downside is the potential for breakage since `lift @Foo` would now fix the RuntimeRep parameter rather than the `a`. This is unfortunate, but I doubt it will show up much. It also unfortunately requires making both `lift` and `liftTyped` methods, when we had just decided to extract `lift` from the class.

I recommend accepting the proposal.

Thanks! Eric

[1]: https://github.com/harpocrates/ghc-proposals/blob/levity-polymorphic-lift/pr... _______________________________________________ ghc-steering-committee mailing list ghc-steering-committee@haskell.org https://mail.haskell.org/cgi-bin/mailman/listinfo/ghc-steering-committee