23 Feb
2016
23 Feb
'16
3:45 a.m.
On Sun, 21 Feb 2016, Jeremy wrote:
Marcin Mrotek wrote
I think that, as far as Foldable is concerned, a tuple is equivalent to Identity, so this instance is indeed useless. However, Foldable is a superclass of Traversable (and it wouldn't make much sense to make these classes unrelated, as one can always define folds with `traverse`), so I've always found it a necessary evil.
Perhaps the case of tuple is evidence that Foldable should *not* be a superclass of Traversable?
For me, pairs should also not be Traversable. I have Writer monad for this purpose.