anchor.diff:    (gl:end))
   
   (defun register-callbacks (tess)
  -  (loop for tess-callback in *tess-callbacks*      
  -     when (compute-applicable-methods 
  -           (tess-callback-generic-function tess-callback) 
  +  (loop for tess-callback in *tess-callbacks*
  +     when (compute-applicable-methods
  +           (tess-callback-generic-function tess-callback)
              (cons tess (loop repeat (tess-callback-arg-count tess-callback) collect t)))
  -     do (glu-tess-callback (glu-tessellator tess) 
  +     do (glu-tess-callback (glu-tessellator tess)
                              (tess-callback-callback-type tess-callback)
                              (get-callback (tess-callback-callback tess-callback)))))
   
   (defun free-tess-data (tess)
  -  "Free data allocated with tess-vertex"
  -  ;; (loop for pointer in (data tess)
  -  ;;    when (and (pointerp pointer) 
  -  ;;              (not (null-pointer-p pointer)))
  -  ;;    do (when (and (pointerp (mem-ref pointer '%gl:double)) 
  -  ;;                  (not (null-pointer-p (mem-ref pointer '%gl:double))))
  -  ;;         (foreign-free (mem-ref pointer '%gl:double)))
  -  ;;      (foreign-free pointer))
  +  "Free data allocated with tess-vertex and tess-combine-callback"
  +  (loop for pointer in (data tess)
  +     when (and (pointerp pointer)
  +               (not (null-pointer-p pointer)))
  +     do (foreign-free pointer))
     (setf (data tess) nil))
   
   (defun save-data-to-free (data-to-free tess)
  
positive.code:         (progn
            (setf (slot-value obj 'glu-tessellator) (glu-new-tess))
            (register-callbacks obj)))))
          
  
  (defmethod tess-delete ((tess tessellator))
    (glu-delete-tess (glu-tessellator tess))
  
negative.code: (defmacro define-tessellation-callbacks (&body callback-specs)
    `(progn
       (setq *tess-callbacks* '())
       ,@(loop for (name callback-type args) in callback-specs
            collect `(define-tessellation-callback ,name ,callback-type ,args))))
  
  (define-tessellation-callbacks
  