> At some point though things get so abstract it's really difficult to understand what's going on. A lot of that comes down to extremely advanced use of Haskel

> At some point though things get so abstract it's really difficult to understand what's going on. A lot of that comes down to extremely advanced use of Haskell's type system. Advanced type systems are valuable, and they're easier to add to FP languages, but I wouldn't consider them to be a fundamentally FP concept. (We see very expressive type systems being included in imperative languages like Rust and Swift these days.) I think it's useful to keep in mind that Haskell is used a lot for research. You don't see Java used as a research sandbox in the same way, so you're not likely to run into run into these kinds of libraries in Java. (Though, as an aside, I consider anything that heavily uses reflection in Java to be nearly as inscrutable.) It's actually impressive just how many of these research-level libraries are practically useful in some way, even if the bar to understanding them is higher. I don't think it's a universal truth that libraries making advanced use of type systems must be difficult to understand. Taking the `lens` library as an example (and I think you were alluding to it, anyway), there's a fairly long-running thread of research around what a "lens" even is, and how they fit into a broader domain of "optics". The `lens` library was created based on one particular representation of lenses, and the community tried to find ways to unify the various kinds of optics in a way that made sense to them. I think the more recent understanding of "profunctor optics" might give us a more accessible route to understanding optics in general, separate from the whole hierarchy of distinct optics you can derive from it.