GNU bug report logs - #30070
27.0.50; cl-print sometimes prints self-referencing objects as #1=#<thing>

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Message #11 received at submit <at> debbugs.gnu.org (full text, mbox):

From: Michael Heerdegen <michael_heerdegen <at> web.de>
To: Stefan Monnier <monnier <at> IRO.UMontreal.CA>
Cc: bug-gnu-emacs <at> gnu.org
Subject: Re: 27.0.50;
 cl-print sometimes prints self-referencing objects as #1=#<thing>
Date: Thu, 11 Jan 2018 15:45:26 +0100

Stefan Monnier <monnier <at> IRO.UMontreal.CA> writes:

> > That gives me "#1=#<thing>".  That's weird because the printed
> > representation of the thing doesn't refer to itself.
>
> Yes, it's a known misfeature (to me at least).  I don't know how we
> could fix it, tho: the cycle-detection is done in a preprocessing phase
> which doesn't know about any print format (nor about cl-print), so by
> the time we learn the the object will be printed as "#<thing>", we have
> already printed "#1=".
>
> To fix it, I have the impression that we'd have to make cl-print a lot
> more complex, and potentially its API as well (e.g. add a matching
> cl-preprocess method additionally to cl-print-object).

Yes, that's what I expected.

Would it make sense to cache what is being printed, post-process it, and
print it at once?


Michael.

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