(defun draw-circle (draw-function x0 y0 radius)
  (labels ((foo (x y)
             (funcall draw-function x y))
           (put (x y m)
             (let ((x+ (+ x0 x))
                   (x- (- x0 x))
                   (y+ (+ y0 y))
                   (y- (- y0 y))
                   (x0y+ (+ x0 y))
                   (x0y- (- x0 y))
                   (xy0+ (+ y0 x))
                   (xy0- (- y0 x)))
               (foo x+ y+)
               (foo x+ y-)
               (foo x- y+)
               (foo x- y-)
               (foo x0y+ xy0+)
               (foo x0y+ xy0-)
               (foo x0y- xy0+)
               (foo x0y- xy0-)
               (multiple-value-bind (y m) (if (plusp m)
                                              (values (1- y) (- m (* 8 y)))
                                              (values y m))
                 (when (<= x y)
                   (put (1+ x)
                        y
                        (+ m 4 (* 8 x))))))))
    (put 0 radius (- 5 (* 4 radius)))
    (values)))