"Mike" == Mike McDonald <mikemac@mikemac.com> writes:
>> To: Andy Hefner <ahefner@gmail.com> >> Date: Wed, 1 Jun 2005 16:20:30 -0500 >> From: rpgoldman@real-time.com >> Or is there a fatal shortsightedness somewhere? Mike> Circular lists? Ah! Good point! I never use those, so I don't think carefully enough about the possibility. I was just worrying about chewing up too much space on bona fide lists, and overlooked the circular list issue. Would it be enough to use some breadcrumb method (e.g., a hash-table) to handle this? Also, is there some sort of glyph that would be an obvious indicator to a user that we have reached a previously-visited node? One concern, of course, is that the breadcrumb trick will only fix circular lists. But recursive invocation of describe-object would leave us open to circularities in graphs represented as lists, unless we had a breadcrumb structure that was a dynamic variable, which seems fairly unpleasant, something like: (defvar *d-obj-breadcrumbs* nil) (defmethod describe-object ((thing list) stream) (format stream "~S is a list~%" thing) (progv (*d-obj-breadcrumbs*) (or *d-obj-breadcrumbs* (make-hash-table :test #'eq)) (loop for x in thing for i from 0 until (and *print-length* (= i *print-length*)) if (gethash x *d-obj-breadcrumbs* nil) do (format stream "<*>") else do (setf (gethash x *d-obj-breadcrumbs*) t) (describe-object x stream) (terpri stream) ;; it would be nice if it were possible to select the ;; ellipsis and make that cause description of further ;; elements. [2005/06/01:rpg] finally (when (< (1+ i) (length thing)) (format stream "...~%"))))) This still seems extremely kludgy, but I would love to see some solution made to work: I hate to give up all hope of poking around inside lists, though, and it sounds like the Do The Right Thing alternative is not going to be with us for a long time. In the meantime, I figure it's at least up to me to provide attempts at a solution for the list to shoot down, if only to prove that I'm serious enough not to just sit around and whine about a missing feature! Best, R