Proposal: Add conspicuously missing Functor instances for tuples

amindfv at amindfv at
Mon Jan 18 21:17:39 UTC 2016

I share Henning's concerns. Can someone provide a realistic example of where an instance for (,,) or (,,,) *is* desirable?


> El 18 ene 2016, a las 15:59, Eric Seidel <eric at> escribió:
>> On Mon, Jan 18, 2016, at 12:44, Christopher Allen wrote:
>> I've addressed this here:
>> 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.
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