83027 lnostdal SW-MVC> (defstruct super (x) (y)) SUPER SW-MVC> (defstruct (sub (:include super)) (z)) SUB SW-MVC> (defmethod test ((obj super)) (format t "X: ~A, Y: ~A~%" (super-x obj) (super-y obj))) #<STANDARD-METHOD TEST (SUPER) {ADFEC41}> SW-MVC> (defmethod test ((obj sub)) (format t "X: ~A, Y: ~A, Z: ~A~%" (super-x obj) (super-y obj) ;; SUB-X and SUB-Y would also work here. (sub-z obj))) ;; But here we must use SUB-Z. #<STANDARD-METHOD TEST (SUB) {BF71C01}> SW-MVC> (test (make-super :x 1 :y 2)) X: 1, Y: 2 NIL SW-MVC> (test (make-sub :x 1 :y 2 :z 3)) X: 1, Y: 2, Z: 3 NIL SW-MVC> 3455728992 None Common Lisp TRUE