@worldsendless Sure, Common Lisp isn't as purely functional as something like Haskell, but programming languages textbooks pretty much universally classify the Lisp family as functional.

@worldsendless I think it is because the LISP languages were the first implementations (that I know of) of Church's lambda calculus, the theoretical basis for functional programming. That said, in practice FP is more of a programming pattern. How "functional" a language is usually depends of how the language facilitate those patterns, which is sometimes subjective. For example, in ELisp or Common Lisp functions are first class citizens, so you can program almost exclusively with pure functions, yet both languages allow global state and mutability. Does that make them less functional? I've never used Clojure, so forgive any misunderstanding on my part, but it seems Rich Hickey thought all the other LISPs facilitate non-functional patterns too much, and included more features in Clojure to encourage a more functional style.