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Re: Predicate for true lists

From: Basil L. Contovounesios
Subject: Re: Predicate for true lists
Date: Sat, 07 Jul 2018 20:06:01 +0300
User-agent: Gnus/5.13 (Gnus v5.13) Emacs/27.0.50 (gnu/linux)

Eli Zaretskii <address@hidden> writes:

>> Cc: address@hidden, address@hidden
>> From: Paul Eggert <address@hidden>
>> Date: Sat, 7 Jul 2018 01:41:38 -0700
>> Eli Zaretskii wrote:
>> > the documentation still doesn't say that 'length' signals
>> > an error for anything that is not a sequence, which is what
>> > proper-list-p is relying on.
>> The proposed implementation of proper-list-p does not rely on such a signal, 
> That's not my reading of the implementation:
>    (and (listp object) (ignore-errors (length object)))
>                         ^^^^^^^^^^^^^

Sorry, I completely overlooked Paul's message[1] that you were replying
to.  I now understand what you meant by your reading of the

Given that the two of you suggested both the need for the doc fix and
its wording, I think you should ignore my patch[2] and push the change
yourself.  Here is yet another updated patch, should you disagree:

>From 79c6e0e80ebdcd0066654d72514dd08891155a77 Mon Sep 17 00:00:00 2001
From: "Basil L. Contovounesios" <address@hidden>
Date: Sat, 7 Jul 2018 19:33:08 +0300
Subject: [PATCH] Fix (length NON-SEQUENCE) documentation

Suggested by Eli Zaretskii <address@hidden> and
Paul Eggert <address@hidden> in the following threads:

* doc/lispref/sequences.texi (Sequence Functions): Mention that
'length' signals a 'wrong-type-argument' also when given a
non-sequencep argument.
 doc/lispref/sequences.texi | 12 +++++++-----
 1 file changed, 7 insertions(+), 5 deletions(-)

diff --git a/doc/lispref/sequences.texi b/doc/lispref/sequences.texi
index 59faf2b4f1..188a345114 100644
--- a/doc/lispref/sequences.texi
+++ b/doc/lispref/sequences.texi
@@ -71,13 +71,15 @@ Sequence Functions
 @cindex list length
 @cindex vector length
 @cindex sequence length
address@hidden bool-vector length
 @cindex char-table length
 @anchor{Definition of length}
-This function returns the number of elements in @var{sequence}.  If
address@hidden is a dotted list, a @code{wrong-type-argument} error is
-signaled; if it is a circular list, a @code{circular-list} error is
-signaled.  For a char-table, the value returned is always one more
-than the maximum Emacs character code.
+This function returns the number of elements in @var{sequence}.  The
+function signals the @code{wrong-type-argument} error if the argument
+is not a sequence or is a dotted list; it signals the
address@hidden error if the argument is a circular list.  For a
+char-table, the value returned is always one more than the maximum
+Emacs character code.
 @xref{Definition of safe-length}, for the related function @code{safe-length}.

[1]: https://lists.gnu.org/archive/html/emacs-devel/2018-07/msg00177.html
[2]: https://lists.gnu.org/archive/html/emacs-devel/2018-07/msg00207.html



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