anchor.diff:    (setf *show-turtle* t)
     (draw-turtle))
   
  -(init-canvas 400 400)+(init-canvas 400 400)
  
positive.code:   (:use :ss))
  
  (in-package :turtle)
  
  (import '(ss-ffi:defun-js))
  
  
negative.code: 
  (defun-js %dom-canvas-width (canvas) "return canvas.width")
  (defun-js %dom-canvas-height (canvas) "return canvas.height")
  
  (defun init-canvas (width height)
    (setf *canvas* (%dom-create *canvas-id* width height)
  