Add syntax for F[Either[A, B]]

[danicheg]

This adds syntax for F[Either[A, B]]. As well as for F[Option[A]], sometimes using monad transformers is not applicable (or F[Either[A, B]] just more preferred).

[danicheg]

@benhutchison I'd be so grateful for a review if you have time for it.

[benhutchison]

Nice! I like the symmetry between F[Option[A]] and F[Either[L, R]].

IIUC, these operations offer a "lite" way to work with 2-deep stacks without needing monad transformers. I wonder if a dedicated section of the documentation is useful to explain the concept?

The simple list of examples in mouse is pretty minimal. Feels like the sophistication & capability of this design may not be visible to users, and these features may get less use than they deserve..?

[danicheg]

IIUC, these operations offer a "lite" way to work with 2-deep stacks without needing monad transformers. I wonder if a dedicated section of the documentation is useful to explain the concept?

The simple list of examples in mouse is pretty minimal. Feels like the sophistication & capability of this design may not be visible to users, and these features may get less use than they deserve..?

Yeah, I have the same thoughts on mouse documentation. Perhaps mouse is ready for its site? I planned to open an issue to discuss it after work on the F[Either[L, R]] syntax.