Lost functionality after merging old monoid library

[Thimoteus]

Taking Conj as an example, the old version has several instances which cannot be used for the newtypes here, since the classes are defined downstream. In particular, it's not possible to do Data.Newtype.ala Conj foldMap, though you can recover the same idea using Data.Lens.Iso.au. In addition, the Alternate newtype has been lost completely.

[LiamGoodacre]

@garyb - I remember us talking about moving Alternate somewhere, but not sure where.

[garyb]

@Thimoteus I don't think we've lost anything, the Newtype instances are still defined, just with the class instead: https://github.com/purescript/purescript-newtype/blob/master/src/Data/Newtype.purs#L48

@LiamGoodacre yeah, there's a PR for that now too 🙂 purescript/purescript-control#50

[Thimoteus]

Ahh! Neat.

[Thimoteus]

With this PR I think all that's missing is the Invariant instance for Alternate. However, in the partial ordering of dependencies, purescript-invariant and purescript-control are incomparable.

[hdgarrood]

I think having either of invariant or control depend on the other ought to be fine; at the moment, both only depend on Prelude. Perhaps having invariant depend on control would be better since I expect the latter is more commonly used.

[hdgarrood]

Closing in favour of purescript/purescript-invariant#9