関数 ad-add-advice

(defun foo ()
  (format "%s %s" "foo" x))
  => foo
(ad-add-advice 'foo
               '(foo-around t t
                            (let ((x "baz"))
                              ad-do-it))
               'around 'first)
  => ((active) (origname . ad-Orig-foo) (around (foo-around t t (let ((x "baz")) ad-do-it))))
(foo)
  error--> Symbol's value as variable is void: x

間違っているようだ…