anchor.diff:            (red:del (list-key list))
             (dolist (id ids)
               (red:rpush (list-key list) id)))))))
  +
  +(defgeneric list-elements (list)
  +  (:documentation "Returns all elements in LIST.")
  +  (:method ((list ohm-list))
  +    (list-range list 0 -1)))
  
positive.code:     (with-connection ()
        (red:lrem (list-key list) 0 (ohm-id element)))))
  
  (defun generic-pop (list pop-func)
    "Returns an object if pop-func delivers an id."
    (let ((id (with-connection ()
                (funcall pop-func (list-key list)))))
      (when id
        (plist->object (element-type list)
                       (fetch-one (element-type list) id)))))
  
negative.code:     (mapcar (lambda (plist)
                (plist->object (element-type list) plist))
              (fetch (element-type list)
                     (list-ids list)))))
  
  (defgeneric list-replace (list new-elements)
    (:documentation "Replaces the LIST elements with NEW-ELEMENTS.")
  