intervals.... no CL Object system?



 
GCL and objects? doesn't seem to work.  

(defstruct (ri (:constructor ri (lo hi)))lo hi );structure for real interval
(defmethod print-object ((a ri) stream)
  (format stream "[~a,~a]"  (ri-lo a)(ri-hi a)))

should make structures of type ri  print like [a,b].
But doesn't.  Does GCL lack CLOS?

I'm using wxmaxima 0.7.3 +maxima 5.13.0, if that matters.

RJF