For that matter, a Python implementation can be written in Python (PyPy). The main point by Lisp-ers is that the language is just code, and a Lisp program can

For that matter, a Python implementation can be written in Python (PyPy). The main point by Lisp-ers is that the language is just code, and a Lisp program can be modified using the same techniques as you would any other code, and it's easy to do - much easier than almost any other language of the time. Definitely easier than implementing Python-in-Python is now. Why would you need it? I believe part of it comes from the idea that you should create a domain-specific way to express your problem, letting the solution naturally fall out. That might not be Lisp, but something that can be converted to Lisp (eg, through a macro) or interpreted by Lisp. If you know how to make a Lisp, you know how to make an interpreter for many other small languages. Not that my opinion carries much weight, but, I dislike the "Lisp can be written in Lisp" argument because I think it's cheating to re-use the garbage collection of the underlying Lisp implementation.