iteration using callbacks

(defun do-query (query callback)
  (format t "doing query ~a~%" query)
  (funcall callback (list 'performed-query query)))

(let* ((queries #(q1 q2 q3 q4 q5 q6))
       (index 0))
  (labels ((callback (result)
             (if (< (incf index) (length queries))
                 (do-query (aref queries index) #'callback)
                 'done)))
    (do-query (aref queries index) #'callback)))
;; =>
;; doing query Q1
;; doing query Q2
;; doing query Q3
;; doing query Q4
;; doing query Q5
;; doing query Q6