>>649 こんなのか？

(defstruct arithmetic-sequence
(init 1) (diff 1) (n 0))
(defvar *my-sequence* nil)
(defun my-init (init diff n)
(setf *my-sequence* (make-arithmetic-sequence :init init :diff diff :n n)))
(defun my-gen ()
(let ((init (arithmetic-sequence-init *my-sequence*))
(diff (arithmetic-sequence-diff *my-sequence*))
(n (arithmetic-sequence-n *my-sequence*)))
(incf (arithmetic-sequence-n *my-sequence*))
(+ init (* n diff))))
(defun my-insert ()
(format "%02d" (my-gen)))
------
(my-init 1 1 0)
=> [cl-struct-arithmetic-sequence 1 1 0]

(my-insert)
"01"

(my-insert)
"02"