Unfortunately we've overloaded the term 'functional programming' a bit too much. Foundation on the lambda calculus is definitely core to most functional languag

Unfortunately we've overloaded the term 'functional programming' a bit too much. Foundation on the lambda calculus is definitely core to most functional languages, and I see how it would be reasonable to think of that as their defining feature, but it seems that the community has instead gravitated towards 'referential transparency' as the key thing. With the former definition, Lisps are definitely functional; with the latter, most of them are definitely not. Most Lispers I know consider e.g. Common Lisp to be a multi-paradigm language, not a functional one, for this reason.