Clojure is not a Lisp [2009]

I haven't read the article, but when I say, in a certain context, that I don't consider clojure a Lisp, what I might mean is that clojure is not descendant from the original McCarty lisp. You can trace Common Lisps or Emacs Lisps roots from MACLISP back to that. In such a context where the definition of "lisp" is sufficiently narrow, I might call languages like clojure and scheme "lisp like languages", or "distant dialects".

It isn't any different from saying Linux is not Unix, but the various BSDs are. It doesn't really matter at all, and when used in the wrong context, such phrases can be confusing.

Clojure is not compatible with Lisp. It's a new Lisp dialect. Just like Logo, Dylan and a few others.

Common Lisp is the successor to Maclisp, which came out of McCarthy's Lisp. Thus you can port most old code to Common Lisp without much pain.

When people switched from Maclisp to Common Lisp, they patched their code. For some time the same code base ran in different dialects.

If you switch from Common Lisp to Clojure, you can rewrite everything or even just forget it anyway.