Re: The convenient method to check/inspect/retrieve the definition/usage of any commands/symbols/operators used in elisp code.

[Omar Polo <op@omarpolo.com>]

(sorry for the delay)

Hongyi Zhao <hongyi.zhao@gmail.com> writes:

> On Sat, Jun 19, 2021 at 11:57 PM Omar Polo <op@omarpolo.com> wrote:
>>
>>
>> Hongyi Zhao <hongyi.zhao@gmail.com> writes:
>>
>> > On Sat, Jun 19, 2021 at 10:48 PM Omar Polo <op@omarpolo.com> wrote:
>> >>
>> >>
>> >> Hongyi Zhao <hongyi.zhao@gmail.com> writes:
>> >>
>> >> > Dear all,
>> >> >
>> >> > Are there any built-in method of Emacs which can let me conveniently
>> >> > check/inspect/retrieve the definition/usage of any
>> >> > commands/symbols/operators used in elisp code at-the-point/in-situ?
>> >> > Say, for the following code snippets:
>> >> >
>> >> > ;;;
>> >> >   (defun fk/company-wordfreq-toggle-language (&optional language)
>> >> >     (interactive)
>> >> >     (setq ispell-local-dictionary (or language
>> >> >                                       (if (string=
>> >> > ispell-local-dictionary "english")
>> >> >                                           "turkish"
>> >> >                                         "english")))
>> >> > [...]
>> >> >   `(progn
>> >> >     ,@(mapcar (lambda (p) `(use-package ,p))
>> >> >               packages)))
>> >> >
>> >> > (use-multiple-packages flycheck
>> >> >                        dash
>> >> >                        )
>> >> >
>> >> > [...]
>> >> > (mapcar #'straight-use-package '(flycheck lsp-mode dash ...))
>> >> >
>> >> > ;or equivalently
>> >> >
>> >> > (defvar my-package-list '(flycheck lsp-mode dash ...))
>> >> > (mapcar #'straight-use-package my-package-list)
>> >> > ;;;
>> >> >
>> >> > I want to find some convenient methods built in Emacs itself with an
>> >> > in-situ manner - by moving the point to the interest position - to
>> >> > check any commands/symbols/operators used in them.
>> >> >
>> >> > Regards
>> >>
>> >> there is M-. (xref-find-definitions) that will jump to the definition of
>> >> the symbol at point (at least in emacs lisp buffers),
>> >
>> > Thank you very much. But still there are some symbols can't find with
>> > this method, say, #'  ,@  ' and so on.
>>
>> #' ' ` , and ,@ aren't symbols, they are reader macros, i.e. special
>> character sequences that the lisp reader expands into some special
>> constructs.  For instance, #'foo is the same as (function 'foo) and 'foo
>> the same as (quote foo).
>>
>> If you M-. with the point over quote (in an elisp buffer) it should jump
>> to eval.c (assuming you have the C source files available).
>>
>> >> and M-, (xref-pop-marker-stack) to jump back.
>> >
>> > I use scratch buffer to test, and it can't jump back there.
>>
>> M-, is meant to be used after one or more M-.
>>
>> For instance:
>>
>> 1. in *scratch* type describe-function
>> 2. press M-. -- it'll jump to help-fns.el.gz
>> 3. move the point over with-help-window (something like ~10 lines below)
>> 4. M-. again -- it'll jump to a different place in the same file
>> 5. go back with M-, -- now you're back in the definition of
>>    describe-function
>> 6. M-, again -- now you're back in the *scratch* buffer
>
> Wonderful explanations. But I still failed to reproduce the M-, , as
> for the other steps you told above except the last two, I can
> reproduce them exactly the same as you described.
>
> See the attachment for the info I saw on the bottom mini-buffer when
> hitting M-, (M- comma).

don't want to sound rude, but could you please refrain from attaching a
whole screenshot just for an error message?  Copying the error, like:

"it says that: buffer is read-only"

it's enough IMHO.  (you'll find a copy of the error message in the
*Messages* buffer if you don't want to type it by hand.)

Now, usually that error is signaled when you try to insert something
into a buffer that read-only.  There can be multiple reasons for that,
but unfortunately I thinks it's something on your end, since I cannot
reproduce with `emacs -Q'.  Make sure that you are hitting M-, and not
the comma alone, or ensure that M-, is bound to xref-pop-marker-stack
and not to something else (C-h k M-,)

As en extreme solution, try to enable the debug-on-error (M-x
toggle-debug-on-error RET) and look at the stacktrace when that error
happens.  (You can use toggle-debug-on-error again to disable it later)

>>
>> >>
>> >> Or you can C-h f or C-h v (describe-function/variable) and then M-n
>> >> (next-history-element) to bring in the symbol at point.
>> >
>> > I meet the following message: M-n is undefined, as shown in the
>> > attached screenshot file.
>>
>> M-n should be defined in some minibuffer maps; with `emacs -Q' I can
>>
>>         C-h v C-h k M-n
>>
>> and it tells me that.
>
> I got the following with your above command sequence:
>
> M-n runs the command next-history-element (found in
> minibuffer-local-must-match-map), which is an interactive compiled
> Lisp function in ‘simple.el’.
>
> It is bound to <XF86Forward>, <next>, M-n, <menu-bar> <minibuf>
> <next>.
>
> (next-history-element N)
>
> Puts next element of the minibuffer history in the minibuffer.
> With argument N, it uses the Nth following element.  The position
> in the history can go beyond the current position and invoke "future
> history."

Yep.  Sorry for giving a long command sequence without any explanation.
`C-h v' is describe-variable, it should enter the minibuffer asking for
a variable to be described.  Then `C-h k' is describe-key, that works in
the minibuffer too.  M-n is bound to next-history-element there too, so
it should work.  When you are over (or at the beginning) of a symbol,
M-n should pull that symbol into the minibuffer.  So with the cursor
over

	toggle-debug-on-error

if I type `C-h f' (describe-function) and then M-n, Emacs automatically
inserts "toggle-debug-on-error" as input in the minibuffer.  Then I can
simply RET to read the documentation of the function :)

> HY
>
>>
>> > M-n runs the command next-history-element (found in
>> > minibuffer-local-must-match-map), which is an interactive compiled
>> > Lisp function in ‘simple.el’.
>>
>> Cheers,
>>
>> > HY
>>