* bug#73886: 29.4; Confusing info about void function cells in Emacs Lisp manual
@ 2024-10-19 14:37 Ulrich Müller
2024-10-19 17:45 ` Eli Zaretskii
2024-10-19 19:08 ` Andreas Schwab
0 siblings, 2 replies; 3+ messages in thread
From: Ulrich Müller @ 2024-10-19 14:37 UTC (permalink / raw)
To: 73886
Section 13.9 "Accessing Function Cell Contents" of the GNU Emacs Lisp
Reference Manual emphasizes the distinction between void and nil
in function cells:
| Note that void is not the same as ‘nil’ or the symbol ‘void’.
| The symbols ‘nil’ and ‘void’ are Lisp objects, and can be stored into
| a function cell just as any other object can be (and ‘void’ can be a
| valid function if you define it with ‘defun’). A void function cell
| contains no object whatsoever.
| You can test the voidness of a symbol's function definition with
| ‘fboundp’. After you have given a symbol a function definition, you
| can make it void once more using ‘fmakunbound’.
Also, for "fboundp":
| This function returns ‘t’ if the symbol has an object in its
| function cell, ‘nil’ otherwise. It does not check that the
| object is a legitimate function.
It seems that the actual behavior does not reflect this, i.e. there
is no distinction between nil and void:
(fmakunbound 'foo)
(fboundp 'foo) ⇒ nil
(fset 'foo nil)
;; according to the manual, the following should return t
;; because nil is a Lisp object:
(fboundp 'foo) ⇒ nil
Is the manual wrong, or am I missing something?
^ permalink raw reply [flat|nested] 3+ messages in thread
* bug#73886: 29.4; Confusing info about void function cells in Emacs Lisp manual
2024-10-19 14:37 bug#73886: 29.4; Confusing info about void function cells in Emacs Lisp manual Ulrich Müller
@ 2024-10-19 17:45 ` Eli Zaretskii
2024-10-19 19:08 ` Andreas Schwab
1 sibling, 0 replies; 3+ messages in thread
From: Eli Zaretskii @ 2024-10-19 17:45 UTC (permalink / raw)
To: Ulrich Müller, Stefan Monnier; +Cc: 73886
> From: Ulrich Müller <ulm@gentoo.org>
> Date: Sat, 19 Oct 2024 16:37:33 +0200
>
> Section 13.9 "Accessing Function Cell Contents" of the GNU Emacs Lisp
> Reference Manual emphasizes the distinction between void and nil
> in function cells:
>
> | Note that void is not the same as ‘nil’ or the symbol ‘void’.
> | The symbols ‘nil’ and ‘void’ are Lisp objects, and can be stored into
> | a function cell just as any other object can be (and ‘void’ can be a
> | valid function if you define it with ‘defun’). A void function cell
> | contains no object whatsoever.
>
> | You can test the voidness of a symbol's function definition with
> | ‘fboundp’. After you have given a symbol a function definition, you
> | can make it void once more using ‘fmakunbound’.
>
> Also, for "fboundp":
>
> | This function returns ‘t’ if the symbol has an object in its
> | function cell, ‘nil’ otherwise. It does not check that the
> | object is a legitimate function.
>
> It seems that the actual behavior does not reflect this, i.e. there
> is no distinction between nil and void:
>
> (fmakunbound 'foo)
> (fboundp 'foo) ⇒ nil
>
> (fset 'foo nil)
> ;; according to the manual, the following should return t
> ;; because nil is a Lisp object:
> (fboundp 'foo) ⇒ nil
>
> Is the manual wrong, or am I missing something?
I think the manual is wrong. I think it tries to explain wrt void
functions the same it says about void variables, but we handle void
variables differently from void functions: void variables have a
distinct value in their value cell, whereas void functions have nil in
their function cell.
Stefan, am I right?
^ permalink raw reply [flat|nested] 3+ messages in thread
* bug#73886: 29.4; Confusing info about void function cells in Emacs Lisp manual
2024-10-19 14:37 bug#73886: 29.4; Confusing info about void function cells in Emacs Lisp manual Ulrich Müller
2024-10-19 17:45 ` Eli Zaretskii
@ 2024-10-19 19:08 ` Andreas Schwab
1 sibling, 0 replies; 3+ messages in thread
From: Andreas Schwab @ 2024-10-19 19:08 UTC (permalink / raw)
To: Ulrich Müller; +Cc: 73886
On Okt 19 2024, Ulrich Müller wrote:
> Is the manual wrong, or am I missing something?
That changed in commit eadf1faa3cb, but the manual wasn't updated.
--
Andreas Schwab, schwab@linux-m68k.org
GPG Key fingerprint = 7578 EB47 D4E5 4D69 2510 2552 DF73 E780 A9DA AEC1
"And now for something completely different."
^ permalink raw reply [flat|nested] 3+ messages in thread
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2024-10-19 14:37 bug#73886: 29.4; Confusing info about void function cells in Emacs Lisp manual Ulrich Müller
2024-10-19 17:45 ` Eli Zaretskii
2024-10-19 19:08 ` Andreas Schwab
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