I've never looked properly into Rebol and don't want to take the time to do so now. But if any HNers know about it, I'd be really interested in seeing a couple of examples of how Rebol does code=data. Specifically, is there a mapping between how Rebol represents code symbolically and how Lisp does it?

The OP did prompt me to take a look at http://en.wikipedia.org/wiki/Carl_Sassenrath, which is actually pretty interesting. I hadn't known about his work on operating systems and the Amiga.