(defmacro rpn (body)
  (rpn-expander body))

(defun rpn-expander (body)
  (mapcar (lambda (x)
                (if (listp x)
                    (rpn-expander x)
                    x))
          (reverse body)))

(rpn ((2 1 +) 2 *))
; => 6

#|
Just a quick stub.

One could easily improve #'RPN-EXPANDER in order to better suit one's needs.
|#