example 01 in http://accomplish-nothing.blogspot.com/2011/01/blog-post.html

gistfile1.cl

(defun square (x) (expt x 2))
;; =>  SQUARE

(define-compiler-macro square (&whole form arg)
  (if (atom arg)
      `(expt ,arg 2)
      (case (car arg)
        (square (if (= (length arg) 2)
                    `(expt ,(nth 1 arg) 4)
                    form))
        (expt   (if (= (length arg) 3)
                    (if (numberp (nth 2 arg))
                        `(expt ,(nth 1 arg) ,(* 2 (nth 2 arg)))
                        `(expt ,(nth 1 arg) (* 2 ,(nth 2 arg))))
                    form))
        (otherwise `(expt ,arg 2)))))
;; =>  SQUARE

(square (square 3))
;; =>  81