anchor.diff:  (let (step-func
         swap-func
         win-size-func
  -      (reg-event-callback-func (lambda (x) x))
  +      (reg-event-callback-func nil)
  +	  (event-callbacks-cache nil)
         (make-current-func (lambda (c s) c s)))
   
     (defun set-step-func (func)
  
positive.code: 
    (defun register-event-listener (function)
      "not external"
      (funcall reg-event-callback-func function)))
  
  ;;----------------------------------------------------------------------
  
  
negative.code:   (defun set-register-event-callback-func (func)
      "Call this and pass the function that will be called when the cepl needs to
       query the window size"
      (setf reg-event-callback-func func)
  	(map nil #'register-event-listener event-callbacks-cache)
  	func)
  
    (defun set-make-gl-context-current-on-surface (func)
      "Call this and pass the function that will be called when the cepl needs to
  