Proposal: Add conspicuously missing Functor instances for tuples

[Eric Seidel]

On Mon, Jan 18, 2016, at 12:44, Christopher Allen wrote:
> I've addressed this here:
> 
> http://bitemyapp.com/posts/2015-10-19-either-is-not-arbitrary.html
> 
> The thousand-papercuts opposition to typeclass instances on the premise
> that a Functor for (a, b, c) maps over the final type not making sense is a
> rejection of how higher kinded types and typeclasses work together. This
> is natural and predictable if one bothers to explain it.

The behavior is indeed predictable, but I think Henning is arguing (and
I would agree) that it is *undesirable*.

That being said, I think the ship has sailed on the "should tuples be a
Functor/etc" discussion. The current proposal is aimed at making the set
of available instances more consistent across tuples, which I'd argue is
a good thing regardless of one's position on the specific class.