The Visitor Pattern is one of the ones that actually does not go away when you have CLOS. That is to say the traversal and visitation part of it doesn't go away, just all the boiler plate around simulating the double dispatch, like needing two methods: accept and visit and whatnot.

Like say we want to visit the elements of a list, which are objects, and involve them with a visiting object:

  (mapcar (lambda (elem)
            (generic-fun visitor elem))
          obj-list)

We write all the method specializations of generic-fun for all combinations of visitor and element type we need and that's it.

Importantly, the traversal function doesn't have to know anything about the visitor stuff. Here we have mapcar, which dates back to before object orientation.