Daniel: Ok, thanks.
I’m acquainted with Forth. I read both Starting Forth and Thinking Forth a few days after posting the above comment, actually; I love the concatenative approach, though I find Forth a bit too low-level for my taste. (My favorite language is currently OCaml, so you can guess how I feel about working without any type system whatsover.) I’ve also looked a little at Factor, but not in depth.
That said, the source to a Forth interpreter in i386 assembly and Forth was one of the single most mind-blowing programming things I’ve ever read. When I saw that the interpreter had a bit for whether the code was being compiled or evaluated, and immediate functions could toggle it at runtime, everything suddenly made sense. So much flexibility emerging from so few constructs!
http://www.annexia.org/_file/jonesforth.s.txt