Add Bifoldable, fixes #94

[adelbertc]

Also:

• Add MonadCombine separate
• Add serializability check for Bifunctor[Xor]

[adelbertc]

Hmm Travis isn't running - closing and re-opening to see what happens.

[codecov-io]

Current coverage is 89.01%

Merging #864 into master will decrease coverage by -0.33% as of 1302795

@@            master    #864   diff @@
======================================
  Files          169     174     +5
  Stmts         2337    2384    +47
  Branches        75      75       
  Methods          0       0       
======================================
+ Hit           2088    2122    +34
  Partial          0       0       
- Missed         249     262    +13

Review entire Coverage Diff as of 1302795

Powered by Codecov. Updated on successful CI builds.

[adelbertc]

There we go

[ceedubs]

It looks like we are combining the Bifunctor and Bifoldable instances in some places but not others. I guess if we are going to go forward with #800 then they will eventually be combined anyway. Was there any particular reason behind when they've been combined and when they haven't?

[adelbertc]

The Bifunctor[Xor] instance was there prior to this PR. It wasn't in other places so I figured I would do those separately, hence #867. However because it looks like we have a use case for #800 I may abandon #867 and add Bitraverse once this is OK'ed and merged :-)

[adelbertc]

As a note there can also be Bifunctor[Validated] but I'll leave that alone since I'll just define Bitraverse for it in a future PR, unless someone beats me to it :-)

[ceedubs]

👍

[ceedubs]

Thanks, @adelbertc!

[adelbertc]

👍 @stew ? :D

[mpilquist]

extends Any with Serializable ?

[adelbertc]

Hmm I see why we would want to do that, but it doesn't seem like we do it in other type classes.. do we?

[mpilquist]

Simulacrum does it automatically. We probably aren't consistent with the F[_,_] type classes though.

[adelbertc]

Alright I added it for Bifoldable, I've added an issue to do it for the others and I'll probably end up doing it in a future PR unless someone beats me to it

[mpilquist]

👍 I didn't see syntax for Bifoldable. Is that intentional?

[adelbertc]

Added some more stuff per @mpilquist 's comments - @ceedubs re-review? :D

[ceedubs]

👍

Out of curiosity, is the reason we want to extend Any so that it's a universal trait that can be extended by values classes? Are there other reasons?

I could potentially see some value in providing methods to extract a Foldable for the left and a Foldable for the right. These could be handy for checking the Foldable laws for each side and for right-biased types like Xor, ensuring that the right Foldable is consistent with the Foldable instance. However, I don't know if people would find themselves using these in real-world code, so even if we did this maybe they should just reside in tests until someone finds themself wanting them?

[ceedubs]

I'll give @mpilquist another chance to review since there were some changes since his last 👍

[mpilquist]

👍