TBH, I think that is a legitimate technical nit. Case classes end up being very useful, but they're not as principled as the ADTs that they're generally used to

TBH, I think that is a legitimate technical nit. Case classes end up being very useful, but they're not as principled as the ADTs that they're generally used to replace, and that shows up in a bunch of weird corner cases. It's one of the prices you pay for trying to cram this stuff into the JVM / OOP universe. Speaking to your sibling comment on Haskell and Kotlin: I also happen to think that Haskell is by far the better-designed language. I think Kotlin does a nice job of cleaning up some of the warts of Java, but I don't really want a better Java -- I just want a better language. Scala is definitely less elegant than Haskell (Haskell/Scalaz-style FP is particularly gross) but there's a large class of problems for which I really do think it's the best language / ecosystem that happens to actually exist.