From: Stefan Monnier via "Bug reports for GNU Emacs, the Swiss army knife of text editors" <bug-gnu-emacs@gnu.org>
To: Lars Ingebrigtsen <larsi@gnus.org>
Cc: 55395@debbugs.gnu.org, "Mattias Engdegård" <mattiase@acm.org>
Subject: bug#55395: What does (1 2 3 . #2) mean?
Date: Fri, 13 May 2022 13:20:51 -0400 [thread overview]
Message-ID: <jwvee0xjqys.fsf-monnier+emacs@gnu.org> (raw)
In-Reply-To: <87ilq931ay.fsf@gnus.org> (Lars Ingebrigtsen's message of "Fri, 13 May 2022 17:22:13 +0200")
>> It may have made more sense before the switch of cycle-detection algorithm
>> from Floyd to Brent. This can be fixed by hand-coding the list iteration
>> and explicitly remembering the index of the tortoise, but would that be
>> correct? What's the spec?
>
> I don't think I've ever considered #x to be meaningful outside of
> print-circle, but I guess if we wanted to have some semantics here, I
> think I would have expected the index of the tortoise? But...
Agreed (and agreed with Andreas as well).
The main goal is to avoid inf-looping and the #NNN chosen is
somewhat arbitrary.
I don't think it's worth it to try and make those #NNN more precise.
If the arbitrariness of the specific #NNN chosen is a problem, we could
replace it with a fixed `#¡cycle!` or something like that (or if we
want it to be more user-readable we could print something like
#cycle:<OBJ> where OBJ is the first N layers of the rest of the cycle,
like (rho 0 2) => (1 2 1 2 . #cycle:(1 2 1 ...))
I'm personally more bothered by the fact that those #NNN use exactly the
same syntax as used with `print-circle` yet they don't have the
same semantics.
Stefan
next prev parent reply other threads:[~2022-05-13 17:20 UTC|newest]
Thread overview: 10+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-05-13 11:32 bug#55395: What does (1 2 3 . #2) mean? Mattias Engdegård
2022-05-13 15:22 ` Lars Ingebrigtsen
2022-05-13 17:20 ` Stefan Monnier via Bug reports for GNU Emacs, the Swiss army knife of text editors [this message]
2022-05-13 19:54 ` Lars Ingebrigtsen
2022-05-13 20:01 ` Mattias Engdegård
2022-05-14 13:45 ` Stefan Monnier via Bug reports for GNU Emacs, the Swiss army knife of text editors
2022-05-18 14:29 ` Mattias Engdegård
2022-05-18 21:16 ` Stefan Monnier via Bug reports for GNU Emacs, the Swiss army knife of text editors
2022-05-23 14:59 ` Mattias Engdegård
2022-05-13 16:08 ` Andreas Schwab
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