Yes, there have been quite a few transitions happening. They didn't happen "for fun", but because it had been felt that the optimal solutions were not found yet

Yes, there have been quite a few transitions happening. They didn't happen "for fun", but because it had been felt that the optimal solutions were not found yet (optimal as in elegant, easy to use, maintainable, ...). Luckily, Haskell's static typing coupled with the extremely helpful error messages of the compiler makes refactoring a cheerful task: If it worked before and all type errors have been fixed, then we can be quite confident that it works again. Many areas have stabilized now. For instance, Edward Kmett's lens package is the de facto standard for all things related to records, getters, setters, and all those things on steroids. (Personally, I love how this turned out. Before lens, we quite frankly had the problem that field accesses were much more painful than they are in mainstream object-oriented languages like Python or Java. Nowadays field accesses are as simple as they are in other languages, and in addition to this we have the flexibility of composable first-class lenses.)