;;;
;;; Třída point
;;;

(defclass point () 
  ((x :initform 0) 
   (y :initform 0))) 

(defmethod r ((point point)) 
  (let ((x (slot-value point 'x)) 
        (y (slot-value point 'y))) 
    (sqrt (+ (* x x) (* y y)))))

(defmethod phi ((point point)) 
  (let ((x (slot-value point 'x)) 
        (y (slot-value point 'y))) 
    (cond ((> x 0) (atan (/ y x))) 
          ((< x 0) (+ pi (atan (/ y x)))) 
          (t (* (signum y) (/ pi 2))))))

(defmethod set-r-phi ((point point) r phi) 
  (setf (slot-value point 'x) (* r (cos phi)) 
        (slot-value point 'y) (* r (sin phi))) 
  point)

(defmethod set-r ((point point) value) 
  (set-r-phi point value (phi point)))

(defmethod set-phi ((point point) value) 
  (set-r-phi point (r point) value))

(defclass circle () 
  ((center :initform (make-instance 'point)) 
   (radius :initform 1)))