Proposal: Add conspicuously missing Functor instances for tuples

Henning Thielemann lemming at
Mon Jan 18 20:32:13 UTC 2016

On Mon, 18 Jan 2016, David Feuer wrote:

> I'd be strongly +1 on that too! Traversable is strong magic.

I am opposed to all these Functor, Foldable, Traversable stuff on tuples 
(including pairs). Why should the last element of a tuple get a special 
treatment? I suspect that if you use such instances you are making 
something dirty. I am afraid that those instance may hide type errors or 
make type errors incomprehensible. E.g. if you get a stack of fmap's 
wrong, you do not get a "no instance for Functor ((,) a)" but instead the 
type mismatch occurs at a different level.

I would never use such an instance. Can I be warned if I accidentally use 
it anyway?

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