custom function getting initialized randomly

custom function getting initialized randomly

[Michael Maurer]

Hello,

I wrote the following function to copy the kill-ring to the scratch
buffer, but it only gets initialized sometimes at the start of emacs,
sometimes not. Why?

(defun copy-to-scratch-on-kill
()
"Copy every kill (delete or yank) to *scratch* buffer."
(let
    ((cur-kill-string
      (current-kill 0 t)))
  (when
      (and
       (not
(equal cur-kill-string ""))
       (not
(equal cur-kill-string prev-kill-string))
       (get-buffer "*scratch*"))
    (with-current-buffer "*scratch*"
      (goto-char
       (point-max))
      (insert cur-kill-string "\n")
      (goto-char
       (point-max))))
  (setq prev-kill-string cur-kill-string)))

(add-hook 'post-command-hook #'copy-to-scratch-on-kill)

Re: custom function getting initialized randomly

[Richard Copley]

On Mon, 27 Mar 2023 at 10:21, Michael Maurer <maurer.michael@gmail.com> wrote:
>
> Hello,
>
> I wrote the following function to copy the kill-ring to the scratch
> buffer, but it only gets initialized sometimes at the start of emacs,
> sometimes not. Why?
>
> (defun copy-to-scratch-on-kill
> ()
> "Copy every kill (delete or yank) to *scratch* buffer."
> (let
>     ((cur-kill-string
>       (current-kill 0 t)))
>   (when
>       (and
>        (not
> (equal cur-kill-string ""))
>        (not
> (equal cur-kill-string prev-kill-string))
>        (get-buffer "*scratch*"))
>     (with-current-buffer "*scratch*"
>       (goto-char
>        (point-max))
>       (insert cur-kill-string "\n")
>       (goto-char
>        (point-max))))
>   (setq prev-kill-string cur-kill-string)))
>
> (add-hook 'post-command-hook #'copy-to-scratch-on-kill)
>

If an error propagates from the hook function (most likely "Kill ring
is empty", signalled by `current-kill`) then Emacs removes the
function from the hook. See the docstring for variable
`post-command-hook`.

Re: custom function getting initialized randomly

[Michael Maurer]

On Mon, 27 Mar 2023 at 15:56, Richard Copley <rcopley@gmail.com> wrote:
>
> On Mon, 27 Mar 2023 at 10:21, Michael Maurer <maurer.michael@gmail.com> wrote:
> >
> > Hello,
> >
> > I wrote the following function to copy the kill-ring to the scratch
> > buffer, but it only gets initialized sometimes at the start of emacs,
> > sometimes not. Why?
> >
> > (defun copy-to-scratch-on-kill
> > ()
> > "Copy every kill (delete or yank) to *scratch* buffer."
> > (let
> >     ((cur-kill-string
> >       (current-kill 0 t)))
> >   (when
> >       (and
> >        (not
> > (equal cur-kill-string ""))
> >        (not
> > (equal cur-kill-string prev-kill-string))
> >        (get-buffer "*scratch*"))
> >     (with-current-buffer "*scratch*"
> >       (goto-char
> >        (point-max))
> >       (insert cur-kill-string "\n")
> >       (goto-char
> >        (point-max))))
> >   (setq prev-kill-string cur-kill-string)))
> >
> > (add-hook 'post-command-hook #'copy-to-scratch-on-kill)
> >
>
> If an error propagates from the hook function (most likely "Kill ring
> is empty", signalled by `current-kill`) then Emacs removes the
> function from the hook. See the docstring for variable
> `post-command-hook`.

Would wrapping the body of the function in (ignore errors ..) be an ok
solution as far as cheap hacks go, or is it too sketchy?

Re: custom function getting initialized randomly

[Richard Copley]

On Mon, 27 Mar 2023 at 15:56, Michael Maurer <maurer.michael@gmail.com> wrote:
> Would wrapping the body of the function in (ignore errors ..) be an ok
> solution as far as cheap hacks go, or is it too sketchy?

Your call, but I would try wrapping it in (when kill-ring ...) before
going that far.

Re: custom function getting initialized randomly

[tomas]

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On Mon, Mar 27, 2023 at 02:56:01PM +0100, Richard Copley wrote:
> On Mon, 27 Mar 2023 at 10:21, Michael Maurer <maurer.michael@gmail.com> wrote:
> >
> > Hello,
> >
> > I wrote the following function to copy the kill-ring to the scratch
> > buffer, but it only gets initialized sometimes at the start of emacs,
> > sometimes not. Why?
> >
> > (defun copy-to-scratch-on-kill
> > ()
> > "Copy every kill (delete or yank) to *scratch* buffer."
> > (let
> >     ((cur-kill-string
> >       (current-kill 0 t)))
> >   (when
> >       (and
> >        (not
> > (equal cur-kill-string ""))
> >        (not
> > (equal cur-kill-string prev-kill-string))
> >        (get-buffer "*scratch*"))
> >     (with-current-buffer "*scratch*"
> >       (goto-char
> >        (point-max))
> >       (insert cur-kill-string "\n")
> >       (goto-char
> >        (point-max))))
> >   (setq prev-kill-string cur-kill-string)))
> >
> > (add-hook 'post-command-hook #'copy-to-scratch-on-kill)
> >
> 
> If an error propagates from the hook function (most likely "Kill ring
> is empty", signalled by `current-kill`) then Emacs removes the
> function from the hook. See the docstring for variable
> `post-command-hook`.

There's more: where does the variable `prev-kill-string' come from?

 - if nobody has set it previously, this will be the error
   killing your hook (this is my hunch)
 - if somebody has, you are lucky if that somebody was you
   (otherwise you are into an entertaining debugging session

If you are using a global variable like that, it makes sense
to declare, document and perhaps initialize it with `defvar'

Another possibility would be to hide it away in a closure [1]
(you are using lexical binding, aren't you?).  Just ask around
here if the concept is unfamiliar to you.

Cheers
-- 
t

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Re: custom function getting initialized randomly

[Michael Maurer]

On Mon, 27 Mar 2023 at 17:21, <tomas@tuxteam.de> wrote:
>
> On Mon, Mar 27, 2023 at 02:56:01PM +0100, Richard Copley wrote:
> > On Mon, 27 Mar 2023 at 10:21, Michael Maurer <maurer.michael@gmail.com> wrote:
> > >
> > > Hello,
> > >
> > > I wrote the following function to copy the kill-ring to the scratch
> > > buffer, but it only gets initialized sometimes at the start of emacs,
> > > sometimes not. Why?
> > >
> > > (defun copy-to-scratch-on-kill
> > > ()
> > > "Copy every kill (delete or yank) to *scratch* buffer."
> > > (let
> > >     ((cur-kill-string
> > >       (current-kill 0 t)))
> > >   (when
> > >       (and
> > >        (not
> > > (equal cur-kill-string ""))
> > >        (not
> > > (equal cur-kill-string prev-kill-string))
> > >        (get-buffer "*scratch*"))
> > >     (with-current-buffer "*scratch*"
> > >       (goto-char
> > >        (point-max))
> > >       (insert cur-kill-string "\n")
> > >       (goto-char
> > >        (point-max))))
> > >   (setq prev-kill-string cur-kill-string)))
> > >
> > > (add-hook 'post-command-hook #'copy-to-scratch-on-kill)
> > >
> >
> > If an error propagates from the hook function (most likely "Kill ring
> > is empty", signalled by `current-kill`) then Emacs removes the
> > function from the hook. See the docstring for variable
> > `post-command-hook`.
>
> There's more: where does the variable `prev-kill-string' come from?
>
>  - if nobody has set it previously, this will be the error
>    killing your hook (this is my hunch)
>  - if somebody has, you are lucky if that somebody was you
>    (otherwise you are into an entertaining debugging session
>
> If you are using a global variable like that, it makes sense
> to declare, document and perhaps initialize it with `defvar'
>
> Another possibility would be to hide it away in a closure [1]
> (you are using lexical binding, aren't you?).  Just ask around
> here if the concept is unfamiliar to you.
>

You're right, that's something I forgot to paste.
The function is preceded by (defvar prev-kill-string "")
I'll take a look at closures and see how far I get on my own, ty.

Re: custom function getting initialized randomly

[tomas]

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On Mon, Mar 27, 2023 at 05:30:50PM +0200, Michael Maurer wrote:
> On Mon, 27 Mar 2023 at 17:21, <tomas@tuxteam.de> wrote:

[...]

> > There's more: where does the variable `prev-kill-string' come from?

[...]

> You're right, that's something I forgot to paste.
> The function is preceded by (defvar prev-kill-string "")
> I'll take a look at closures and see how far I get on my own, ty.

Ah, OK. I'll shut up, then :-D

Cheers
-- 
t

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custom function getting initialized randomly

[Michael Maurer]

Hello,

I wrote the following function to copy the kill-ring to the scratch
buffer, but it only gets initialized sometimes at the start of emacs,
sometimes not. Why?

(defun copy-to-scratch-on-kill
()
"Copy every kill (delete or yank) to *scratch* buffer."
(let
    ((cur-kill-string
      (current-kill 0 t)))
  (when
      (and
       (not
(equal cur-kill-string ""))
       (not
(equal cur-kill-string prev-kill-string))
       (get-buffer "*scratch*"))
    (with-current-buffer "*scratch*"
      (goto-char
       (point-max))
      (insert cur-kill-string "\n")
      (goto-char
       (point-max))))
  (setq prev-kill-string cur-kill-string)))

(add-hook 'post-command-hook #'copy-to-scratch-on-kill)