anchor.diff:     (glMatrixMode GL_MODELVIEW)
      (glLoadIdentity)
   
  +(gl:set-userdata
      (let* ((time _ (clock)))
  -      (list time))
  -)
  +      (list time)))
   
   ; draw
  +(gl:set-renderer
   (lambda (oldtime)
      (let* ((time _ (clock)))
   
  
positive.code: 
     (glEnd)
  
     (list time))))
negative.code:          (setx! glows x y 0)))))))
  
  
  (gl:set-window-title "Digital Rain")
  
  ; init
     (glShadeModel GL_SMOOTH)
     (glClearColor 0 0 0 1.0)
  
  