(defun greet (tgt)
  (format t "hi, ~A!~%" tgt))

(let 
  ((readers '("foo" "bar" "qux")))
  (defun get-all-readers ()
    (copy-list readers))

  (defun add-reader (rdr)
    (setf readers
      (cons rdr
        (get-all-readers)))))

(mapcar 
  #'(lambda (rdr) (greet rdr))
  (get-all-readers))