lawful lenses

R.lensProp and R.lensIndex aren’t quite lawful, as @scott-christopher explained in https://github.com/ramda/ramda/issues/1281#issuecomment-209444109.

Scott, have you any interest in working on Sanctuary equivalents of Ramda’s lens functions, which would use the Maybe type where appropriate to satisfy the lens laws?

[davidchambers]

@protoEvangelion and @coodoo, lenses will be the next major addition to Sanctuary.

As it may be of interest, I will share the backstory. In order to define van Laarhoven lenses, which have the desirable property of being compatible with S.compose, we need two types: Identity a and Constant a b. The former exists as sanctuary-identity; the latter will exist once sanctuary-js/sanctuary-constant#1 has been merged. As I was working on sanctuary-constant I was also working on fantasyland/fantasy-land#315, a proposal that will, if accepted, necessitate changes to every Fantasy Land -compliant ADT. It seemed sensible at the time to release a new major version of the Fantasy Land specification before publishing any new ADT packages.

In mid 2019 I started a full-time job, as I was running out of money. My ambitious plans may have made sense when I had a lot of time to devote to Sanctuary, but when the demands on my time increased I should have reconsidered them. The Fantasy Land changes are themselves several weeks of full-time work, as they involve updating fantasy-laws and the many Sanctuary ADTs.

Let’s finalize and merge sanctuary-js/sanctuary-constant#1 without waiting for fantasyland/fantasy-land#315. We will then have what we need to define S.lens, S.view, S.over, and S.set. Later, once FL5 has been published, we will release sanctuary-constant@2.0.0.

[protoEvangelion]

@davidchambers is there anything on the roadmap still for implementing lenses?