How to do basic object oriented in common list. Only for fun, if you actually want OO, use CLOS.

oo-in-common-lisp.lisp

(defun inverse-collatz (n)
  "returns a list with one or two values that collatz to n"
  (cons (* 2 n)
	(let ((other-result (/ (- n 1) 3)))
	  (if (integerp other-result)
	      (list other-result)
	      nil))))


;; use lambda closure to access lexically scoped variable "starting-list"
(defun inverse-collatz-grower-maker (starting-list)
  ;; TODO put a "let" here for "self" so call between methods is possible
  (list
   (cons 'get-starting-list
	 #'(lambda ()
	     starting-list))
   (cons 'set-starting-list
	 #'(lambda (new-val)
	     (setf starting-list new-val)))
   (cons 'expand-n
	 #'(lambda (n)
	     (if (member n starting-list)
		 (setf starting-list
		       (remove-duplicates (append (inverse-collatz n) starting-list))))))))


(defun dot (alist key &rest args)
  (apply (cdr (assoc key alist)) args))

;; minimal example of structure it works on
(dot (list (cons 'foo #'(lambda (x y) (+ x y)))) 'foo 4 2)
;; >> 6

(defvar foo1 (inverse-collatz-grower-maker '(1)))
;; >> foo1

(dot foo1 'get-starting-list)
;; >> (1)
(dot foo1 'set-starting-list '(1 2 3))
;; >> (1 2 3)
(dot foo1 'expand-n 1)
;; >> (0 1 2 3) ;; 0 should be redacted ;(
(dot foo1 'expand-n 2)
;; >> (4 0 1 2 3)
(dot foo1 'expand-n 3)
;; >> (6 4 0 1 2 3)
(dot foo1 'expand-n 4)
;; >> (8 6 4 0 1 2 3)