Add fold, foldMap, foldM, foldMaybe

[natefaubion]

No description provided.

[hdgarrood]

I wonder if the new FoldableWithIndex type class might be relevant here? https://pursuit.purescript.org/packages/purescript-foldable-traversable/3.4.0/docs/Data.FoldableWithIndex

[natefaubion]

I had no idea this class existed 😆

[garyb]

But yeah, adding WithIndex stuff for both Map and StrMap sounds good too. I think we can do that?

[garyb]

Of course we can, Map is a Functor.

[paf31]

Will these go into instances then? If not, can we use the xWithKey naming scheme?

[natefaubion]

I was gunning for API parity with StrMap. I'm happy to make modifications if we want to shift over to instances, but we should do the same for StrMap, and it will be a breaking change (or we can add deprecated warnings).

[paf31]

I agree they should ideally match. Maybe let's just add the instances on top of what you have now, and we can remove them later.

[hdgarrood]

I'm not sure if it is necessarily a problem to provide monomorphic functions as well as an instance providing those same functions in general - sometimes the former are more convenient, I think.