Common Lispでクイックソートの練習

quicksort.lisp

;; -*- mode: lisp; coding: utf-8 -*-

(defun quick-sort(lst &optional (test-func #'<))
  (if (<= (length lst) 1)
      lst
    (let (upper
	  lower
	  (pivot (car lst)))
      (dolist (v (cdr lst))
	(if (funcall test-func v pivot)
	    (push v upper)
	  (push v lower)))
      (append (quick-sort upper test-func)
	      (list pivot)
	      (quick-sort lower test-func)))))

(setf data '(3 1 4 1 5 9 2 6 5 3 5 8 9 7 9))
(format t "Data: ~S~%" data)
(format t "Asc:  ~S~%" (quick-sort data))
(format t "Desc: ~S~%" (quick-sort data #'>))