Depend on assoc for instances

[phadej]

assoc provides Bifunctor p => Swap p and Assoc p type-classes.

Currently assoc depends on bifunctors to provide instances for Flip, Biff etc types defined in bifunctors.

But now we have a light compatibility package bifunctor-classes-compat.

So I propose a following dependency rearrangement:

• assoc depends on bifunctor-classes-compat and provides type-classes and instances for things in base
• bifunctors depends on assoc to provide Swap and Assoc instances for extra bifunctors defined here
• e.g. lens is not really affected, as it still depends on both assoc and bifunctors. lens defines Wrapped instance for Biff, Clown ... etc, otherwise it could drop (at least direct) bifunctors dependency as well)
• but e.g. these could drop bifunctors dependency as it only needs Bifunctor type-class and type-classes defined in assoc package.

This will be breaking change in assoc but only a minor change in bifunctors.

How does this sound?

[RyanGlScott]

That sounds reasonable to me. Are you willing to help migrating the instances?

[phadej]

Sure. I'll prepare a patch shortly

[phadej]

Done in #121