GNU bug report logs - #73886
29.4; Confusing info about void function cells in Emacs Lisp manual

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From: Ulrich Müller <ulm <at> gentoo.org>
To: 73886 <at> debbugs.gnu.org
Subject: bug#73886: 29.4; Confusing info about void function cells in Emacs Lisp manual
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?

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