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?