anchor.diff:  
   (defparameter +sheep-size+ 2.0)
   (defparameter +sheep-grazing-cooldown-time+ 2.0)
  +(defparameter +sheep-eating-speed+ 1.0)
   
   (defparameter +food-color+ (p2dg:make-color-4 0 0.4 0 1))
   (defparameter +food-size+ 2.0)
  
positive.code:    (angular-speed :initarg :speed
                    :initform p2dm:+pi+
                    :accessor player-angular-speed)))
  
  (defmethod draw-entity ((player player))
    (with-slots (position orientation color)
  
negative.code: (defun update-all-boids (world dt)
    (let ((boids (boids world)))
      (loop for boid in boids
         do (update-entity boid world dt))))
  
  (defun draw-all-boids ()
    (loop for boid in (boids *world*)
       do (draw-entity boid)))
  
  (defun spheres-collide-p (pos1 pos2 r1 r2)
    (< (p2dm:distance-between-vectors-squared pos1 pos2)
  