Since he mentioned self-infecting Lisp functions (which seems to me to be unrelated to his main topic but whatever), I should mention that I put together a Lisp

Since he mentioned self-infecting Lisp functions (which seems to me to be unrelated to his main topic but whatever), I should mention that I put together a Lisp self-infecting "virus" (so to speak) a long time ago. My original version -- which was beautiful and I have conveniently forgotten -- used a quine to deliver the payload. But here's a version I whipped up for HN a few weeks back which gives you the idea. ;; run this on SBCL (sb-ext:unlock-package :common-lisp) (let (syms) (do-symbols (s :common-lisp) (if (fboundp s) (push s syms))) (labels ((worm (sym) (let ((next (elt syms (random (length syms)))) (old (symbol-function sym))) (format t "~%Worm attacks ~a, next target is ~a!~%" sym next) (setf (symbol-function sym) (lambda (&rest args) (when next (worm next) (setf next nil)) (apply old args)))))) (worm '+))) ;; now try adding some numbers (and so on)