; -*- lisp -*-

(defun sqr (x) (* x x))

(defclass Point2d ()
  ((x :accessor x :initarg :x)
   (y :accessor y :initarg :y)))

(defclass Point3d (Point2d)
  ((z :accessor z :initarg :z)))

(defun translate (p x)
  (let ((p (clone p)))
    (setf (x p) (+ (x p) 1)) p))

(defmethod clone ((p Point2d)) (make-instance 'Point2d :x (x p) :y (y p)))
(defmethod clone ((p Point3d)) (make-instance 'Point3d :x (x p) :y (y p) :z (z p)))

(defmethod to-string ((p Point2d)) (format nil "[~F, ~F]" (x p) (y p)))
(defmethod to-string ((p Point3d)) (format nil "[~F, ~F, ~F]" (x p) (y p) (z p)))

(defmethod my-length ((p Point2d)) (sqrt (+ (sqr (x p)) (sqr (y p)))))
(defmethod my-length ((p Point3d)) (sqrt (+ (sqr (x p)) (sqr (y p)) (sqr (z p)))))


(setq p2d (make-instance 'Point2d :x 3 :y 4))
(setq p3d (make-instance 'Point3d :x 1 :y 2 :z 2))
(setq l (list p2d p3d))

(defun test (p)
  (list (my-length p) (to-string (translate p 1))))

(list (test p2d) (test p3d) (mapcar #'my-length l)
      ; after translate, we still have a Point3d
      (z (translate p3d 1)))