newLISP the true champion of homoiconicity

Can your Lisp do this, /prog/?

(define (plus-minus a b)
  (begin
    (setf (nth '(1 2 0) plus-minus) (if (= (nth '(1 2 0) plus-minus) -) + -))
    (+ a b)))

(plus-minus 10 2)
8
(plus-minus 10 2)
12

newLISP treats code literally as data unlike Common Lisp or Scheme.

>>28
In that case the macro m has lexical scope, and it uses the mf function defined in the let statement for its code transformer. It is powerful to let any user defined lisp function to assist your macro. And we are creeping up on first class macros, but we haven't gotten there yet.