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Subject: |
Documentation bug: Emacs Lisp Manual should say quoting does not cons explicitly in quoting section. related to bug#9469 |
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Date: |
Mon, 12 Sep 2011 23:01:23 +0800 |
Relevant page here:
http://www.gnu.org/s/emacs/manual/html_node/elisp/Quoting.html
I was confused and always assumed that
'(a . b)
is simply short hand for
(cons 'a 'b)
Reading stackexchange, it seems at least some other people are under
this impression as well. This works a majority of the time, but when
it fails it's really surprising.
In fact, the manual already has an example of this pit-fall in the
nconc section:
http://www.gnu.org/software/emacs/elisp/html_node/Rearrangement.html
I think the quoting section should give an explicit warning with a
reference to the nconc example.
--
Le
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--- Begin Message ---
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Subject: |
Re: specific manual text suggestion |
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Date: |
Fri, 16 Sep 2011 10:14:39 -0400 |
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User-agent: |
Gnus/5.13 (Gnus v5.13) Emacs/24.0.50 (gnu/linux) |
> My terminology may be not quite right, but if I read something like
> this, the difference would be much clearer.
Thanks for your sample text. I tweaked it a bit to make it hopefully
even more explicit, see patch below.
Stefan
--- src/eval.c 2011-09-09 01:06:52 +0000
+++ src/eval.c 2011-09-16 14:09:39 +0000
@@ -475,6 +475,14 @@
DEFUN ("quote", Fquote, Squote, 1, UNEVALLED, 0,
doc: /* Return the argument, without evaluating it. `(quote x)' yields
`x'.
+Warning: `quote' does not construct its return value, but just returns
+the value that was pre-constructed by the Lisp reader (see info node
+`(elisp)Printed Representation').
+This means that '(a . b) is not identical to (cons 'a 'b): the former
+does not cons. Quoting should be reserved for constants that will
+never be modified by side-effects, unless you like self-modifying
+code. See the common pitfall in info node `(elisp)Rearrangement' for
+an example of unexpected results when a quoted object is modified.
usage: (quote ARG) */)
(Lisp_Object args)
{
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