[throwaway9848]

Languages I think you should know:

C, Java, Bash, Javascript, one out of {Perl,Python,Ruby}, and perhaps a functional language like Lisp or Clojure. Each one will make your understanding of programming more comprehensive.

What Java offers is that it's actually a pretty idealistic language in its approach to OOP, to the point that it irritates the hell out of most of us with all the necessary boilerplate. Practically speaking, too, there are a lot of Java jobs (and probably will be for a while) and it's not very idiomatic so there's a lot of overlap w/ other languages, vs say, Prolog.

Also, by "know" I mean, have written a non-"hello world" application but not necessarily having expertise in it.

[meowface]

I like the functional paradigm and enjoy writing functional code, but personally, any time I look at Lisp or Clojure my eyes just completely glaze over. I understand how powerful S-expressions can be (source code can be data and vice versa), but reading them is a massive pain.

So, I've been learning Haskell and Scala instead. Is learning a Lisp-based language a necessity to be a robust, professional developer, do you think?

[throwaway9848]

No, I just was suggesting learning about any functional language, those two just came to mind first.