Does the command loop even look at the return values of commands executed?

Does the command loop even look at the return values of commands executed?

[Marcin Borkowski]

Hi all,

I am pretty sure that the command loop discards anything returned by
a command invoked via a keybinding or M-x, but I couldn't find anything
about it in the Elisp reference.  Is that true?  Is it documented
anywhere?  (I don't necessarily think it /needs/ to, but I'm quite
curious; also, I don't want to lie in my book;-).)

TIA,

-- 
Marcin Borkowski
http://mbork.pl

Re: Does the command loop even look at the return values of commands executed?

[Eli Zaretskii]

> From: Marcin Borkowski <mbork@mbork.pl>
> Date: Thu, 26 Aug 2021 07:32:36 +0200
> 
> I am pretty sure that the command loop discards anything returned by
> a command invoked via a keybinding or M-x, but I couldn't find anything
> about it in the Elisp reference.  Is that true?  Is it documented
> anywhere?

Yes, we ignore the value returned by commands.  No, it isn't
documented, AFAICT.

RE: [External] : Re: Does the command loop even look at the return values of commands executed?

[Drew Adams]

> > I am pretty sure that the command loop discards anything returned by
> > a command invoked via a keybinding or M-x, but I couldn't find anything
> > about it in the Elisp reference.  Is that true?  Is it documented
> > anywhere?
> 
> Yes, we ignore the value returned by commands.  No, it isn't
> documented, AFAICT.

Just for info, in case it's somehow relevant to
Marcin: There is global variable `values'.
(elisp) node `Eval' tells us:

___
Variable: values
  The value of this variable is a list of the values returned by all
  the expressions that were read, evaluated, and printed from buffers
  (including the minibuffer) by the standard Emacs commands which do
  this.  (Note that this does _not_ include evaluation in ‘*ielm*’
  buffers, nor evaluation using ‘C-j’, ‘C-x C-e’, and similar
  evaluation commands in ‘lisp-interaction-mode’.)  The elements are
  ordered most recent first.

       (setq x 1)
            ⇒ 1
       (list 'A (1+ 2) auto-save-default)
            ⇒ (A 3 t)
       values
            ⇒ ((A 3 t) 1 ...)

  This variable is useful for referring back to values of forms
  recently evaluated.  It is generally a bad idea to print the value
  of ‘values’ itself, since this may be very long.  Instead, examine
  particular elements, like this:

       ;; Refer to the most recent evaluation result.
       (nth 0 values)
            ⇒ (A 3 t)
       ;; That put a new element on,
       ;;   so all elements move back one.
       (nth 1 values)
            ⇒ (A 3 t)
       ;; This gets the element that was next-to-most-recent
       ;;   before this example.
       (nth 3 values)
            ⇒ 1
___

Although it doesn't apply to `C-x C-e', it does apply
to `M-:'.

Re: [External] : Re: Does the command loop even look at the return values of commands executed?

[Stephen Berman]

On Thu, 26 Aug 2021 16:52:02 +0000 Drew Adams <drew.adams@oracle.com> wrote:

>> > I am pretty sure that the command loop discards anything returned by
>> > a command invoked via a keybinding or M-x, but I couldn't find anything
>> > about it in the Elisp reference.  Is that true?  Is it documented
>> > anywhere?
>>
>> Yes, we ignore the value returned by commands.  No, it isn't
>> documented, AFAICT.
>
> Just for info, in case it's somehow relevant to
> Marcin: There is global variable `values'.
> (elisp) node `Eval' tells us:
>
> ___
> Variable: values
>   The value of this variable is a list of the values returned by all
>   the expressions that were read, evaluated, and printed from buffers
>   (including the minibuffer) by the standard Emacs commands which do
>   this.
[...]

In Emacs 28 the doc string of `values' says "This variable is obsolete
as of Emacs 28.1 and should not be used."  It's also mentioned in Emacs
28 NEWS, but the Emacs 28 Elisp manual hasn't been updated on this yet.

Steve Berman

Re: [External] : Re: Does the command loop even look at the return values of commands executed?

[Emanuel Berg via Users list for the GNU Emacs text editor]

Stephen Berman wrote:

> In Emacs 28 the doc string of `values' says "This variable
> is obsolete as of Emacs 28.1 and should not be used." It's
> also mentioned in Emacs 28 NEWS, but the Emacs 28 Elisp
> manual hasn't been updated on this yet.

Here, which is

  GNU Emacs 28.0.50 (build 3, x86_64-pc-linux-gnu, cairo
  version 1.16.0) of 2021-08-02

the docstring for `values' say

  values is a variable defined in ‘src/lread.c’.
  Its value is nil

    Probably introduced at or before Emacs version 1.1.

  Documentation:
  List of values of all expressions which were read, evaluated and printed.
  Order is reverse chronological.

Maybe an Emacs 28.1 thing ...

-- 
underground experts united
https://dataswamp.org/~incal

Re: [External] : Re: Does the command loop even look at the return values of commands executed?

[Stephen Berman]

On Fri, 27 Aug 2021 10:12:02 +0200 Emanuel Berg via Users list for the GNU Emacs text editor <help-gnu-emacs@gnu.org> wrote:

> Stephen Berman wrote:
>
>> In Emacs 28 the doc string of `values' says "This variable
>> is obsolete as of Emacs 28.1 and should not be used." It's
>> also mentioned in Emacs 28 NEWS, but the Emacs 28 Elisp
>> manual hasn't been updated on this yet.
>
> Here, which is
>
>   GNU Emacs 28.0.50 (build 3, x86_64-pc-linux-gnu, cairo
>   version 1.16.0) of 2021-08-02
>
> the docstring for `values' say
>
>   values is a variable defined in ‘src/lread.c’.
>   Its value is nil
>
>     Probably introduced at or before Emacs version 1.1.
>
>   Documentation:
>   List of values of all expressions which were read, evaluated and printed.
>   Order is reverse chronological.
>
> Maybe an Emacs 28.1 thing ...

It was changed in this commit:

commit 627a02467508140d213a68c9eed6cb78a5e94860
Author:     Lars Ingebrigtsen <larsi@gnus.org>
Commit:     Lars Ingebrigtsen <larsi@gnus.org>
CommitDate: Tue Feb 9 16:28:38 2021 +0100

    Note that the `values' variable is now obsolete
    
    * src/lread.c (syms_of_lread): Note that it's obsolete in the doc
    string (because we can't mark it as obsolete "properly" yet,
    because that leads to compilation warnings when somebody
    (let (values) ... values).


On Fri, 27 Aug 2021 10:13:24 +0200 Emanuel Berg via Users list for the GNU Emacs text editor <help-gnu-emacs@gnu.org> wrote:

> Stephen Berman wrote:
>
>> This is true of Emacs 27 but in Emacs 28 `=' and `+' are
>> buttonized in *Help*.
>
> Not here which is
>
>   GNU Emacs 28.0.50 (build 3, x86_64-pc-linux-gnu, cairo
>   version 1.16.0) of 2021-08-02

It was changed in this commit:

commit 25dadca0d175aa7f9f1654314f90af64cdcb68fd
Author:     Basil L. Contovounesios <contovob@tcd.ie>
Commit:     Basil L. Contovounesios <contovob@tcd.ie>
CommitDate: Sun Jan 10 13:37:38 2021 +0000

    Hyperlink symbol names without word syntax in Help
    
    * lisp/emacs-lisp/lisp-mode.el (lisp-el-font-lock-keywords-2)
    (lisp-cl-font-lock-keywords-2): Allow single-character symbol names.
    * lisp/help-mode.el (help-xref-symbol-regexp): Also match symbol
    names starting with symbol syntax (bug#6601, bug#24309).
    * test/lisp/help-mode-tests.el (help-mode-tests-xref-button): Test
    hyperlink creation for function names without symbol syntax.

> Please use
>
>   C-u M-x emacs-version RET
>
>   GNU Emacs 28.0.50 (build 3, x86_64-pc-linux-gnu, cairo
>   version 1.16.0) of 2021-08-02

GNU Emacs 28.0.50 (build 14, x86_64-pc-linux-gnu, GTK+ Version 3.24.29, cairo version 1.17.4) of 2021-08-26

I think more relevant is the value of `emacs-repository-version':

"ee2ffd9c9eb33a17307f36ff58caec1ba79878d2"


On Fri, 27 Aug 2021 10:51:22 +0200 Emanuel Berg via Users list for the GNU Emacs text editor <help-gnu-emacs@gnu.org> wrote:

> Yeah ... where/how did you get 28.1?
>
> I did what I usually do and got same old 28.0.50.
>
> From https://git.savannah.gnu.org/git/emacs.git
>
> #! /bin/zsh
> #
> # this file:
> #   http://user.it.uu.se/~embe8573/conf/.zsh/install-emacs
> #   https://dataswamp.org/~incal/conf/.zsh/install-emacs
>
> local EMACS_SRC=https://git.savannah.gnu.org/git/emacs.git
> local EMACS_DIR=~/src
>
> emacs-install-prepare () {
>     sudo apt-get -qq update
>     sudo apt-get install build-essential
>     sudo apt-get build-dep emacs
> }
>
> emacs-src-reset () {
>     cd $EMACS_DIR
>     git reset --hard
>     git clean -xdf
>     git pull $EMACS_SRC
> }
> alias emacs-reset-src=emacs-src-reset
>
> emacs-src-get () {
>     cd $EMACS_DIR
>     git clone $EMACS_SRC
> }
> alias emacs-get-src=emacs-src-get
>
> # autogen.sh
> # configure --with-x-toolkit=no
> # make
> # sudo make install

I don't know why you're failing to get the current sources.  I also use
`git pull'.  I have an account so the URL I use
srb@git.sv.gnu.org:/srv/git/emacs.git but I don't think that should make
a difference.  Maybe your emacs-install-prepare function is interfering.

Steve Berman

Re: [External] : Re: Does the command loop even look at the return values of commands executed?

[Emanuel Berg via Users list for the GNU Emacs text editor]

Stephen Berman wrote:

> I think more relevant is the value of `emacs-repository-version':
>
> "ee2ffd9c9eb33a17307f36ff58caec1ba79878d2"

OK, I have

  558065531beaaae78810508f267415c6953e8e47

so that explains it. Err

-- 
underground experts united
https://dataswamp.org/~incal

Re: [External] : Re: Does the command loop even look at the return values of commands executed?

[Eli Zaretskii]

> Date: Fri, 27 Aug 2021 10:12:02 +0200
> From:  Emanuel Berg via Users list for the GNU Emacs text editor <help-gnu-emacs@gnu.org>
> 
> Stephen Berman wrote:
> 
> > In Emacs 28 the doc string of `values' says "This variable
> > is obsolete as of Emacs 28.1 and should not be used." It's
> > also mentioned in Emacs 28 NEWS, but the Emacs 28 Elisp
> > manual hasn't been updated on this yet.
> 
> Here, which is
> 
>   GNU Emacs 28.0.50 (build 3, x86_64-pc-linux-gnu, cairo
>   version 1.16.0) of 2021-08-02
> 
> the docstring for `values' say
> 
>   values is a variable defined in ‘src/lread.c’.
>   Its value is nil
> 
>     Probably introduced at or before Emacs version 1.1.
> 
>   Documentation:
>   List of values of all expressions which were read, evaluated and printed.
>   Order is reverse chronological.

Your build is old; update from Git soon is recommended.

RE: [External] : Re: Does the command loop even look at the return values of commands executed?

[Drew Adams]

> > Just for info, in case it's somehow relevant to
> > Marcin: There is global variable `values'.
> > (elisp) node `Eval' tells us: ...
> 
> In Emacs 28 the doc string of `values' says "This variable is obsolete
> as of Emacs 28.1 and should not be used."  It's also mentioned in Emacs
> 28 NEWS, but the Emacs 28 Elisp manual hasn't been updated on this yet.

Yes, I know - but it's good to spread the word.
[Oh, and there is no Emacs 28 release (yet).]

Variable `values' has existed since ~Day One.
It's in Emacs 20, and I believe I recall it
from The Beginning.  R.I.P.

Re: Does the command loop even look at the return values of commands executed?

[Marcin Borkowski]

On 2021-08-26, at 14:51, Eli Zaretskii <eliz@gnu.org> wrote:

>> From: Marcin Borkowski <mbork@mbork.pl>
>> Date: Thu, 26 Aug 2021 07:32:36 +0200
>> 
>> I am pretty sure that the command loop discards anything returned by
>> a command invoked via a keybinding or M-x, but I couldn't find anything
>> about it in the Elisp reference.  Is that true?  Is it documented
>> anywhere?
>
> Yes, we ignore the value returned by commands.  No, it isn't
> documented, AFAICT.

Thanks!

-- 
Marcin Borkowski
http://mbork.pl