(defclass generic-list ()
  (
    (contents :accessor contents)
  )
)

(defmethod make-empty ((alist generic-list))
  (setf (contents alist) nil)
)

(defmethod is-empty ((alist generic-list))
  (null (contents alist))
)

(defmethod insert-item ( item (alist generic-list) )
   (setf (contents alist) (cons item (contents alist)))
)

(defmethod remove-item ((alist generic-list))
  (let
    (
      (result (first (contents alist)))
    )

    (setf (contents alist) (rest (contents alist)))
    result
  )
)

;; note: stack would be better in its own file

(defclass stack (generic-list)
  (
  )
)

;; note: queue would be better in its own file

(defclass queue (generic-list)
 (
 )
)

(defmethod insert-item ( item (alist queue) )
  (setf (contents alist) (append (contents alist) (list item)))
)

;; an example of using the stack class
;; note: my-stack is global

(setf my-stack (make-instance 'stack))
(make-empty my-stack)
(insert-item 1 my-stack)
(insert-item 2 my-stack)
(insert-item 3 my-stack)
(is-empty my-stack)
(remove-item my-stack)
(describe my-stack)