GNU logs - #21915, boring messages

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Subject: bug#21915: write inconsistent about #nil
Resent-From: Zefram <zefram@HIDDEN>
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Date: Sat, 14 Nov 2015 01:46:56 +0000
From: Zefram <zefram@HIDDEN>
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The write function is inconsistent about whether it distinguishes between
#nil and ():

scheme@(guile-user)> '(#nil . a)
$1 = (#nil . a)
scheme@(guile-user)> '(a . #nil)
$2 = (a)

Thee latter behaviour, emitting #nil as if it were (), breaks the usual
write/read round-tripping, and the traditional correspondence between
equal? and matching of written representation.  Admittedly those standards
are not absolute, nor is the extent to which they're expected to hold
documented, but #nil is clearly sufficiently atomic to be the kind of
value to which one would expect them to apply.  For these reasons,
if a consistent behaviour is to be chosen, I think it should be to
consistently distinguish the values.

I think the behaviour should be consistent.  The values should be
distinguished or not without regard to the context in which they arise
within an s-expression.

Whatever is done, even if it's to endorse the inconsistency, the behaviour
should be documented, with rationale.

-zefram

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From: help-debbugs@HIDDEN (GNU bug Tracking System)
To: Zefram <zefram@HIDDEN>
Subject: bug#21915: Acknowledgement (write inconsistent about #nil)
Message-ID: <handler.21915.B.144746562619636.ack <at> debbugs.gnu.org>
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Date: Sat, 14 Nov 2015 01:48:02 +0000

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Subject: bug#21915: write inconsistent about #nil
References: <20151114014656.GT13455@HIDDEN>
In-Reply-To: <20151114014656.GT13455@HIDDEN>
Resent-From: Taylan Kammer <taylan.kammer@HIDDEN>
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Resent-Date: Fri, 14 May 2021 13:36:01 +0000
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To: 21915 <at> debbugs.gnu.org, Zefram <zefram@HIDDEN>
From: Taylan Kammer <taylan.kammer@HIDDEN>
Message-ID: <b69985c6-3bfa-c853-023f-f7ac60236bca@HIDDEN>
Date: Fri, 14 May 2021 15:34:56 +0200
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Hi Zefram,

this is an interesting issue.  Here's a related one:

  https://bugs.gnu.org/48318

I think first of all #nil and '() should actually be equal?
to each other.  After all, both represent the empty list,
and checking structural equality between lists is one of the
common uses of equal?.

It might also be good, in addition, to make the Scheme writer
write (foo . #nil) as (foo . #nil).  The positive is that it
would make bugs in Elisp compatibility easier to see by not
masking the fact that one has #nil instead of () at the end
of a list.  The only negative I can think of is that it would
be mildly annoying to see (foo bar . #nil) where you expected
to see (foo bar), but I don't think that's ever really harmful.

Thoughts?

- Taylan

Message sent to bug-guile@HIDDEN:

Subject: bug#21915: write inconsistent about #nil
Resent-From: Taylan Kammer <taylan.kammer@HIDDEN>
Original-Sender: "Debbugs-submit" <debbugs-submit-bounces <at> debbugs.gnu.org>
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Resent-Date: Fri, 14 May 2021 21:32:02 +0000
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To: 21915 <at> debbugs.gnu.org
From: Taylan Kammer <taylan.kammer@HIDDEN>
References: <20151114014656.GT13455@HIDDEN>
 <b69985c6-3bfa-c853-023f-f7ac60236bca@HIDDEN>
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Date: Fri, 14 May 2021 23:31:30 +0200
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On 14.05.2021 15:34, Taylan Kammer wrote:
> 
> It might also be good, in addition, to make the Scheme writer
> write (foo . #nil) as (foo . #nil).  The positive is that it
> would make bugs in Elisp compatibility easier to see by not
> masking the fact that one has #nil instead of () at the end
> of a list.  The only negative I can think of is that it would
> be mildly annoying to see (foo bar . #nil) where you expected
> to see (foo bar), but I don't think that's ever really harmful.
> 

FWIW here's a tiny patch that realizes this change.

- Taylan

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tags 48315 + patch
tags 21915 + patch
tags 39221 + patch
tags 39601 + patch
tags 40584 + patch

Last modified: Sat, 15 May 2021 18:00:02 UTC

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