On Fri, 19 Jul 2019, Carter Schonwald wrote:
Hey Russell, is there any expository or tech reporty exposition of the differences in formulation and the why's wherefores of the new major release? (i'm genuinely curious since i'm quite wimpy in the lens foo)
There hasn't been a change in formulation of used in lens-family, rather the grate-like and adapter-like new formulations have been added along side. Perhaps you are asking about the different formulations between different lens libraries? I'm not sure what the best expositions are. "Profunctor Optics: Modular Data Accessors" by Pickering, Gibbons, and Wu at https://www.cs.ox.ac.uk/people/jeremy.gibbons/publications/poptics.pdf seems like a reasonably good presentation of the implementations. A library user is somewhat insualted from the details of the different implementations through the library combinators, but some differences remain. For example, in lens-family's van Laarhoven implementation, I require explicit casting between Grate-like, Adatper-like, and Lens-like optics, whereas a profunctor based implementation would treat all three class of optics uniformly. That said, you could have a van Laarhoven implementaion that uses Adapter-like for all optics and keep Identity functor wrappers around. This isn't done in lens-family in order to keep backwards compatibility with the original Lens-like optics. I've put out a new relase because I've started using grid optics in my own work. For example, I use 'bend' to create bit-wise parsing of 256-bit hash values @ https://github.com/ElementsProject/simplicity/blob/d1f8298b2ea557073e2358ac0..., and I use an 'fe' grid @ https://github.com/ElementsProject/simplicity/blob/67c838a7b31e7fc555a027950..., etc. to create instances of Arbitrary @ https://github.com/ElementsProject/simplicity/blob/67c838a7b31e7fc555a027950... As far as I know, Kmett's lens library doesn't yet have much support for grates and grids, but I'm sure that will change. That said, a good tutorial on how to program with these new grates and grid optics would be useful. Unfortunately, I think these will take time to be developed. -- Russell O'Connor http://r6.ca/ ``My friends, love is better than anger. Hope is better than fear. Optimism is better than dispair. So let us be loving, hopeful and optimistic. And we'll change the world.'' -- Jack Layton