From: Marcin Borkowski <mbork@mbork.pl>
To: help-gnu-emacs@gnu.org
Subject: Re: Are two symbols `equal' iff they are `eq'?
Date: Sun, 09 Aug 2015 21:41:24 +0200 [thread overview]
Message-ID: <87io8os10b.fsf@mbork.pl> (raw)
In-Reply-To: <83si7spbna.fsf@gnu.org>
On 2015-08-09, at 20:19, Eli Zaretskii <eliz@gnu.org> wrote:
>> From: Marcin Borkowski <mbork@mbork.pl>
>> Date: Sun, 09 Aug 2015 17:45:31 +0200
>>
>> >> >From the capitalization I would guess that QUIT is a C macro. From its
>> >> name I would guess that anything after it is irrelevant;-). Well,
>> >> joking aside, I found its definition in the source; do I get it right
>> >> that it quits if something like C-g happens?
>> >
>> > Yes.
>> >
>> >> If yes, I'd be curious why it is here.
>> >
>> > To allow the user to interrupt a (potentially) long operation.
>>
>> That's obvious, I just wondered why at this point.
>
> Because that point is traversed every recursion, so we check for C-g
> on each "iteration", so to say.
Ah, I see. That does make sense. Thanks!
>> >> Apart from that, it seems that I was right: `equal' for
>> >> symbols just calls `eq' (C EQ, not Lisp eq, to be more precise).
>> >
>> > What else could it possibly do?
>>
>> It could e.g. compare the string representation, so two symbols with the
>> same name but in different obarrays, or one interned and the other not,
>> could be equal but not eq.
>
> I'm sure you understand how all of those would make no sense as
> "equality" of any kind.
Frankly, I don't. I don't really have enough experience with the very
ideas of a "symbol", of "interning" and of an "obarray" (in particular,
having many of them) to see this. I guess when I learn more Lisp (maybe
Common Lisp?), I'll see this. But I believe you, and this is enough for
me now - I'll just try to keep that issue in my mind during my further
studies, and maybe I'll get it some day. I'm not in a hurry, you
know;-).
>> (I'm not sure whether this would be useful, though - just a
>> thought.)
>
> If it won't be useful, why would someone do it?
If not, then not. I agree.
Best,
--
Marcin Borkowski
http://octd.wmi.amu.edu.pl/en/Marcin_Borkowski
Faculty of Mathematics and Computer Science
Adam Mickiewicz University
next prev parent reply other threads:[~2015-08-09 19:41 UTC|newest]
Thread overview: 24+ messages / expand[flat|nested] mbox.gz Atom feed top
[not found] <mailman.7993.1439079676.904.help-gnu-emacs@gnu.org>
2015-08-09 0:31 ` Are two symbols `equal' iff they are `eq'? Joost Kremers
2015-08-09 5:16 ` Ian Zimmerman
2015-08-09 7:30 ` Marcin Borkowski
2015-08-09 14:05 ` Michael Heerdegen
2015-08-09 15:10 ` Marcin Borkowski
2015-08-09 15:19 ` Eli Zaretskii
2015-08-09 15:45 ` Marcin Borkowski
2015-08-09 18:19 ` Eli Zaretskii
2015-08-09 19:41 ` Marcin Borkowski [this message]
2015-08-10 15:26 ` Nicolas Richard
[not found] ` <mailman.8007.1439097407.904.help-gnu-emacs@gnu.org>
2015-08-09 5:21 ` Rusi
2015-08-09 5:33 ` Ian Zimmerman
2015-08-09 7:42 ` Marcin Borkowski
2015-08-09 14:03 ` Michael Heerdegen
2015-08-09 14:42 ` Marcin Borkowski
2015-08-09 14:47 ` Michael Heerdegen
[not found] ` <mailman.8011.1439106166.904.help-gnu-emacs@gnu.org>
2015-08-09 15:38 ` Joost Kremers
2015-08-09 0:20 Marcin Borkowski
2015-08-09 1:52 ` Emanuel Berg
2015-08-09 7:44 ` Marcin Borkowski
2015-08-09 15:28 ` Drew Adams
2015-08-09 15:46 ` Marcin Borkowski
2015-08-09 16:38 ` Drew Adams
[not found] ` <mailman.8032.1439135226.904.help-gnu-emacs@gnu.org>
2015-08-09 15:59 ` Stefan Monnier
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