COMMENT ⊗   VALID 00002 PAGES
C REC  PAGE   DESCRIPTION
C00001 00001
C00002 00002	 functions for computing with cyclic list structures
C00004 ENDMK
C⊗;
;;; functions for computing with cyclic list structures

(defun count (x) (car (count1 x nil)))

;;; This seems right, but version in cyclic[e80,jmc] probably is
;;; more complicated for some reason.
(defun count1 (x u) (if
			(atom x) (cons 1 u)
			(member x u) (cons 0 u)
			((lambda (w) (foo (car w) (count1 (cdr x) (cdr w))))
				(count1 (car x) (cons x u)))))

(defun foo (n u) (cons (+ n (car u)) (cdr u)))

(defun cycle1 (u v) (if (null (cdr u)) (rplacd u v) (cycle1 (cdr u) v)))

(defun cycle (u) (cycle1 u u))

((lambda (x) nil)(setq a (cycle '(a b c))))

(defun nodes1 (x u) (if (member x u)	u
			(atom x)	(cons x u)
			(nodes1 (cdr x) (nodes1 (car x) (cons x u)))))

(defun count2 (x) (length (nodes1 x nil)))

;;; Carolyn's idea for counting and listing at once.
;;; The argument is a list <<node> <count> <seen>>
(defun nodesc (w) (if
	(member (car w) (caddr w)) 
	(list (cadr w) (caddr w))
	(atom (car w))
	 (cons (add1 (cadr w)) (list (cons (car w) (caddr w))))
	 (nodesc (cons (car (car w))
                       (nodesc (foo w))))))

(progn (setq z (list ((lambda (w) (rplaca w w)) '(a.b)) 0 nil)) 0) 

(setq zz '((a.a) 0 nil))

(defun foo (w) (list (cdr (car w)) (add1 (cadr w)) (cons (car w) (caddr w))))