anchor.diff:    (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))
   
  
positive.code:     :initform (error "must supply parent"))))
  
  (defmethod herd ((sheep sheep))
    (actors (environment sheep)))
  
  (defmethod update ((mover mover))
    (with-slots (x y max-speed environment heading behavior) mover
  
negative.code:                    (:lonely light-blue)
                     (:isolated dark-blue)
                     (otherwise white))))
        (unless *color-sheep-by-status-p* (setf color white))
        (cairo-translate cr x y)
        (let ((head-size (* .5 size))
              (head-location (* .9 size)))
  
          (when *heading-indicators-visible-p* (draw-heading-indicator cr sheep))
          (when *sheep-labels-visible-p* (draw-label cr sheep))
  
          ;;; draw body
          (cairo-rotate cr heading)
  