anchor.diff:    (setf *show-turtle* t)
     (draw-turtle))
   
  -(init-canvas 400 400)+(init-canvas 400 400)
  
positive.code: 
  (defun-js %dom-canvas-width (canvas) "return canvas.width")
  (defun-js %dom-canvas-height (canvas) "return canvas.height")
  
  ;; forward declarations to avoid compiler warnings
  ;; should figure out a better way to do this
  (defun draw-turtle ())
  (defun hide-turtle ())
  
  (defun init-canvas (width height)
    (setf *canvas* (%dom-create *canvas-id* width height)
  
negative.code:   (:use :ss))
  
  (in-package :turtle)
  
  (export '(draw-turtle
            hide-turtle
            show-turtle
            save-excursion
            without-pen
            orientation
            forward
            backward
            set-color
            left
            right
            penup
            pendown
            clear
            triangle))
  
  (import '(ss-ffi:defun-js))
  
  