GNU bug report logs - #49647
27.2; Reference Manual sec. 10.2.4; Incorrect example for indirect-function

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Message #5 received at submit <at> debbugs.gnu.org (full text, mbox):

From: Scott Marks <scott.c.marks <at> gmail.com>
To: bug-gnu-emacs <at> gnu.org
Subject: 27.2; Reference Manual sec. 10.2.4;
 Incorrect example for indirect-function
Date: Mon, 19 Jul 2021 14:38:34 -0400

[Message part 1 (text/plain, inline)]

If one copies the example:


Here is how you could define indirect-function in Lisp:


(defun indirect-function (function)

  (if (symbolp function)

      (indirect-function (symbol-function function))

    function))


this code will throw due to infinite recursion when invoked as


(indirect-function nil)


The fix is obvious: wrap (symbolp function) with (and function ...)


I don't think this would distract from the point of the example.


Hope this helps

Scott


In GNU Emacs 27.2 (build 1, x86_64-apple-darwin18.7.0, NS appkit-1671.60
Version 10.14.6 (Build 18G95))

 of 2021-03-27 built on builder10-14.porkrind.org

Windowing system distributor 'Apple', version 10.3.2022

System Description:  macOS 11.4


Recent messages:

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[Message part 2 (text/html, inline)]

Message #8 received at 49647 <at> debbugs.gnu.org (full text, mbox):

From: Michael Heerdegen <michael_heerdegen <at> web.de>
To: Scott Marks <scott.c.marks <at> gmail.com>
Cc: 49647 <at> debbugs.gnu.org
Subject: Re: bug#49647: 27.2; Reference Manual sec. 10.2.4; Incorrect
 example for indirect-function
Date: Tue, 20 Jul 2021 01:59:06 +0200

Scott Marks <scott.c.marks <at> gmail.com> writes:

> If one copies the example:

You mean from the manual, (info "(elisp) Function Indirection") I think.

>  Here is how you could define indirect-function in Lisp:
>
>  (defun indirect-function (function)
>
>    (if (symbolp function)
>
>        (indirect-function (symbol-function function))
>
>      function))
>
> this code will throw due to infinite recursion when invoked as
>
> (indirect-function nil)
>
> The fix is obvious: wrap (symbolp function) with (and function ...)

In my opinion your analysis is correct and the fix is good.

I leave it to the second reader to make the change.


Michael.

Message #11 received at 49647 <at> debbugs.gnu.org (full text, mbox):

From: Lars Ingebrigtsen <larsi <at> gnus.org>
To: Michael Heerdegen <michael_heerdegen <at> web.de>
Cc: Scott Marks <scott.c.marks <at> gmail.com>, 49647 <at> debbugs.gnu.org
Subject: Re: bug#49647: 27.2; Reference Manual sec. 10.2.4; Incorrect
 example for indirect-function
Date: Tue, 20 Jul 2021 14:06:59 +0200

Michael Heerdegen <michael_heerdegen <at> web.de> writes:

> In my opinion your analysis is correct and the fix is good.
>
> I leave it to the second reader to make the change.

Now done.

-- 
(domestic pets only, the antidote for overdose, milk.)
   bloggy blog: http://lars.ingebrigtsen.no

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