Lisp is not an immutable language. There's setf and setq for assigning; nconc, nsubst, and the destructive list operations; rplaca and rplacd; etc. It's easy

Lisp is not an immutable language. There's setf and setq for assigning; nconc, nsubst, and the destructive list operations; rplaca and rplacd; etc. It's easy to write Lisp that doesn't mutate (let), or use constructs that hide it (dolist, dotimes, etc.), but mutable data has been in Lisp since the beginning. That said, there are languages in the family that don't allows mutation, but they're a small minority.