Editing Visitor pattern (section)

==== Notes ====
The <code>other-object</code> parameter is superfluous in <code>traverse</code>. The reason is that it is possible to use an anonymous function that calls the desired target method with a lexically captured object:

<syntaxhighlight lang=Lisp>(defmethod traverse (function (a auto)) ;; other-object removed
  (with-slots (elements) a
    (dolist (e elements)
      (funcall function e)))) ;; from here too

  ;; ...

  ;; alternative way to print-traverse
  (traverse (lambda (o) (print o *standard-output*)) a)

  ;; alternative way to do-something with
  ;; elements of a and integer 42
  (traverse (lambda (o) (do-something o 42)) a)</syntaxhighlight>

Now, the multiple dispatch occurs in the call issued from the body of the anonymous function, and so <code>traverse</code> is just a mapping function that distributes a function application over the elements of an object. Thus all traces of the Visitor Pattern disappear, except for the mapping function, in which there is no evidence of two objects being involved. All knowledge of there being two objects and a dispatch on their types is in the lambda function.