GNU bug report logs - #47677
[PATCH] condition-case success continuation

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Message #26 received at 47677 <at> debbugs.gnu.org (full text, mbox):

From: Mattias Engdegård <mattiase <at> acm.org>
To: Lars Ingebrigtsen <larsi <at> gnus.org>
Cc: Stefan Monnier <monnier <at> iro.umontreal.ca>, 47677 <at> debbugs.gnu.org
Subject: Re: bug#47677: [PATCH] condition-case success continuation
Date: Tue, 13 Apr 2021 10:52:54 +0200

13 apr. 2021 kl. 09.38 skrev Lars Ingebrigtsen <larsi <at> gnus.org>:

>>  ((:catch TAG) BODY...)
> 
> I'm not quite sure I understand the use case for this -- we already have
> a general catch/throw infrastructure, so this sounds like a somewhat odd
> addition.

Oh, it was just proof-of-concept code to show that such a generalisation would be possible should it be desired later. It's not part of the immediate proposal. Sorry about the confusion.

Our present `catch` has the same flaw as `condition-case` in that it does not give access to the success continuation, leading to hacks similar to the one you mentioned. We could extend `catch` instead, maybe like this:

  (catch TAG :in BODY-FORM :success VAR SUCCESS-FORM)

but what if you want to catch multiple tags, or both throws and errors? The constructs don't compose; nesting them hides the success continuation of the inner forms.

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