+;;; Returns a list of members of LIST. Useful for dealing with circular lists.
+;;; For a dotted list returns a secondary value of T -- in which case the
+;;; primary return value does not include the dotted tail.
+(defun list-members (list)
+ (when list
+ (do ((tail (cdr list) (cdr tail))
+ (members (list (car list)) (cons (car tail) members)))
+ ((or (not (consp tail)) (eq tail list))
+ (values members (not (listp tail)))))))
+