I was asked to join a team of scala developers. Most except one had started learning about 6 months earlier. I was asked to learn it while making small contributions to the project. I quickly found out that there were statements that could be interpreted in multiple ways, can't remember now what it was. Then I got stuck on something and even our seasoned very enthusiastic Scala developer could not solve it. I then and there decided not to pursue learning the language and quickly have myself transferred to another team. It's a difficult language, one should not spend thinking on the language but spend time thinking about the problem itself. Probably what I say is not doing justice to Scala as I was just a newbie but I did not have those problems with Clojure which is another not that mainstream language.
And that's the whole problem with Scala. When you work with it, you are having a battle with types and compiler more often than you should. Funny but it is not the first typed language I had to write code in. Never did I have to do so much unnecessary dancing around and asking senior colleagues for help. I guess not all of us are capable of grasping such expressiveness at the cost of such complexity. The majority just need simpler tools to be productive.
Going full FP in Scala with Scalaz and "tagless final" (I still have no clear idea what's that) and whatever else that's hip, leads to madness. Sure you can write maximally polymorphic code. Great. But you end up doing the extractions/refactors that the type system and the compiler allows, not those that would help the code the most. Because those are too slow (too much boxing and GC churn), or the compiler has a bug (or the library) so you end up putting a TODO comment in the code with a link to a github issue.
Or it's a feature that's not supported by Scala, so you end up with a FP spaghetti. :(
