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

[Hongyi Zhao <hongyi.zhao@gmail.com>]

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On Wed, Jun 23, 2021 at 4:56 PM Hongyi Zhao <hongyi.zhao@gmail.com> wrote:
>
> On Wed, Jun 23, 2021 at 3:49 PM Omar Polo <op@omarpolo.com> wrote:
> >
> > (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-,)
>
> Thank you very much. Because of my negligence, the real input sequence
> I've tried before is as follows:
>
> (C-h k M-')

Then I put the cursor on the result buffer which describing M-'  , then I
hit M-' again. Now, the following screenshot will be triggered:


[image: 2021-06-23_16-59.png]
I hope this time I clearly expressed all of my key sequences.

HY
>
> >
> > 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 :)
>
> Wonderful. Got it. Thank you very much again.
>
> HY
>
> >
> > > 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
> > >>
> >
>
>
> --
> Assoc. Prof. Hongyi Zhao <hongyi.zhao@gmail.com>
> Theory and Simulation of Materials
> Hebei Vocational University of Technology and Engineering
> NO. 552 North Gangtie Road, Xingtai, China



-- 
Assoc. Prof. Hongyi Zhao <hongyi.zhao@gmail.com>
Theory and Simulation of Materials
Hebei Vocational University of Technology and Engineering
NO. 552 North Gangtie Road, Xingtai, China

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