anchor.diff:    ;; {TODO} what does state mean
     (newtonbodysetsimulationstate (%body-ptr body) state))
   
  -(defun body-get-skeleton ()
  +(defun body-get-skeleton (body)
     ;; {TODO} how are we meant to handle skeletons?
     (newtonbodygetskeleton (%body-ptr body)))
   
  
positive.code: 
  (defun (setf body-force-torque-callback) (callback body)
    (newtonbodysetforceandtorquecallback
     (%body-ptr body) '%body-apply-force-and-torque)
    (setf (%body-force-torque-callback body) callback))
  
  ;;------------------------------------------------------------
  
negative.code:   (with-foreign-array (v3 force-vec3 '(:array :float 3))
      (newtonbodyaddforce (%body-ptr body) v3)))
  
  (defun body-add-impluse (body delta-vec3 &optional (position-vec3 (v! 0 0 0)))
    (with-foreign-array (d3 delta-vec3 '(:array :float 3))
      (with-foreign-array (p3 position-vec3 '(:array :float 3))
        (newtonbodyaddimpulse (%body-ptr body) d3 p3))))
  