Style improvements

[podiki]

(via this comment on Reddit):

Mostly looks good, but I've got some style suggestions. Number one, I'd make constructors for your objects instead of inlining make-instance calls. For example:

(defun make-rect (x y w h)
  (let ((r (make-instance 'rect :x1 x :y1 y)))
    (setf (x2 r) (+ (x1 r) width)
          (y2 r) (+ (y1 r) height)
          (center r) (cons (floor (/ (+ (x1 r) (x2 r)) 2)) (floor (/ (+ (y1 r) (y2 r)) 2))))
    rect))

I also rearranged some functions to suggest some style improvements. I'd try to minimize declaring variables just to setf them later... usually you can just add a nested let, or use let*.