Re:Comparing the Same Project in Rust, Haskell, C++, Python,...
by tathougies on Sunday June 16, 2019 @05:00PM
(#20197860)
My biggest use case for lenses that I miss in other languages is the ability to interact with all elements of a collection, or elements in deeply nested collections.
For example, if I had a list of records with a field named 'categories' holding a list of objects with a field named 'tags', and I wanted to get all of these names in one list, without nested loops, lens makes it easy 'record ^.. categories . each . tags . each' or I could update them all, etc. It's just so easy to do this kind of data munging with lens that writing fors, whiles, etc in other languages is painful.
In practice, the main reason people use it is to work around the deficiencies of Haskell's built-in record system:
>I never built fclabels because I wanted people to use my software (maybe just a bit), but I wanted a nice solution for Haskell’s non-composable record labels.(http://fvisser.nl/post/2013/okt/11/why-i-dont-like-the-lens-...)
The other features of lenses don't strike me as particularly useful. YMMV. I'd also question the quality of the library. It's full of junk like e.g. http://hackage.haskell.org/package/lens-4.17.1/docs/src/Cont..., which is just an invitation to write unreadable code.