Haskell Foldable Wats (Was: Add conspicuously missing Functor instances for tuples)

[Henning Thielemann]

On Wed, 24 Feb 2016, Christopher Allen wrote:

> Were any of these objections put forward in 1993 when Mark P. Jones 
> published on constructor classes [1] ? Everything about this follows 
> directly and uniquely from that design. 
> [1]: http://web.cecs.pdx.edu/~mpj/pubs/fpca93.pdf

I don't think so. As I have shown there could have been generalizations of 
'length' where 'length (a,b) = 2'. That would not be a generalization via 
Foldable, though. And again, I do not propose to implement 'length (a,b) = 
2'.