anchor.diff:      :initform nil)))
   
   (defclass mover (actor)
  -  (
  -   (behavior
  +  ((behavior
       :accessor behavior
       :initform nil)
      (heading
  
positive.code: (defgeneric draw-heading-indicator (cr object))
  (defgeneric herd (sheep))
  (defgeneric expiredp (behavior current-time))
  
  (defclass actor (wired-object)
    ((x
  
negative.code:   (cairo-move-to cr (+ 5 x) (+ 5 y))
    (cairo-select-font-face cr "serif" 0 1)
    (cairo-set-font-size cr 10.0)
    (cairo-set-source-color cr black)
    (cairo-show-text cr text)
    (cairo-restore cr))
  
  