Improving the instances of Data.Functor.{Product,Sum}

chessai . chessai1996 at
Sat Mar 14 14:10:47 UTC 2020

I can second Richard's estimation of QuantifiedConstraints, I have used
them a lot in my own code since they were in HEAD. I consider it a
sufficiently stable feature to include in base or any library.

On Sat, Mar 14, 2020, 4:16 AM Richard Eisenberg <rae at> wrote:

> On Mar 14, 2020, at 4:14 AM, Eric Mertens <emertens at> wrote:
> The last thing I'd heard about quantified constraints was that they were
> buggy and I've been avoiding relying on them. (I should probably review
> that assumptions at some point.)
> Without expressing an opinion about chessai's proposal (which I have not
> really thought about): quantified constraints are in good shape and ready
> for prime time. They have limitations (e.g. you can't mention a type family
> to the right of the =>), but when they are valid, they work well. I'll
> never swear that a feature is bug-free, but I think it's reasonable to
> consider using quantified constraints in `base`.
> Richard
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