Re: Using button-label in pcase

[Stephen Berman]

On Mon, 24 Jul 2023 22:40:03 +0000 uzibalqa <uzibalqa@proton.me> wrote:

> ------- Original Message -------
> On Tuesday, July 25th, 2023 at 10:36 AM, Stephen Berman
> <stephen.berman@gmx.net> wrote:
>
>
>> On Mon, 24 Jul 2023 22:24:33 +0000 uzibalqa uzibalqa@proton.me wrote:
>>
>> > ------- Original Message -------
>> > On Tuesday, July 25th, 2023 at 9:51 AM, Stephen Berman
>> > stephen.berman@gmx.net wrote:
>> >
>> > > On Mon, 24 Jul 2023 21:35:44 +0000 uzibalqa uzibalqa@proton.me wrote:
>> > >
>> > > > ------- Original Message -------
>> > > > On Tuesday, July 25th, 2023 at 8:07 AM, Stephen Berman
>> > > > stephen.berman@gmx.net wrote:
>> > > >
>> > > > > On Mon, 24 Jul 2023 19:14:27 +0000 uzibalqa uzibalqa@proton.me wrote:
>> > > > >
>> > > > > > Want to print some text as a result of clicking a button. With the
>> > > > > > code below
>> > > > > > I end up with
>> > > > > >
>> > > > > > (wrong-type-argument integer-or-marker-p nil)
>> > > > > > buffer-substring-no-properties(nil nil)
>> > > > > > button-label(#<overlay in no buffer>)
>> > > > > > (let* ((val (button-label button))) (if (equal val '"[FA]") (let 
>> > > > > > nil
>> > > > > > (insert qrh-c))))
>> > > > > > (closure ((button . #<overlay in no buffer>)) nil (let* ((val
>> > > > > > (button-label button))) (if (equal val '"[FA]") (let nil (insert
>> > > > > > qrh-c)))))()
>> > > > > > help--window-setup("Help" (closure ((button . #<overlay in no 
>> > > > > > buffer>))
>> > > > > > nil (let* ((val (button-label button))) (if (equal val '"[FA]") 
>> > > > > > (let nil
>> > > > > > (insert qrh-c))))))
>> > > > > > qrh-b(#<overlay in no buffer>)
>> > > > > > button-activate(#<overlay in no buffer> t)
>> > > > > > push-button(3 t)
>> > > > > >
>> > > > > > What is going on. Is there a fix?
>> > > > > >
>> > > > > > (defconst qrh-c "[FA] Some Text")
>> > > > > >
>> > > > > > (defun qrh-b (button)
>> > > > > > "Prints information about how to install emacs."
>> > > > > > (with-help-window (help-buffer)
>> > > > > > (pcase (button-label button)
>> > > > > > ("[FA]" (insert qrh-c))) ))
>> > > > > >
>> > > > > > (defun qrh-a ()
>> > > > > > "Prints information about how to install emacs."
>> > > > > > (interactive)
>> > > > > > (with-help-window (help-buffer)
>> > > > > > (insert-button "[FC]"
>> > > > > > 'action 'qrh-b 'follow-link t) ))
>> > > > >
>> > > > > The error is raised because qrh-b calls with-help-window with the 
>> > > > > Help
>> > > > > buffer current, but with-help-window erases the buffer, so when
>> > > > > `(button-label button)' is evaluated, there is no button and this
>> > > > > signals the error.
>> > > >
>> > > > That what was wrong then.
>> > >
>> > > That there was no button. When you execute your command qrh-a and then
>> > > in the resulting Help buffer press the button, it disappears.
>> > >
>> > > > > If you want to use the existing Help buffer, just remove the call to
>> > > > > with-help-window in qrh-b.
>> > > >
>> > > > > However, Help buffers are read-only, so
>> > > > > trying to insert text will raise another error. To avoid this, you 
>> > > > > can
>> > > > > let-bind buffer-read-only in qrh-b.
>> > > >
>> > > > I do not experience the problem you mention. What error are you 
>> > > > referring to,
>> > > > and how can it be triggered ?
>> > >
>> > > Did you remove the call the with-help-window in qrh-b and correct the
>> > > match condtion (or change the string in qrh-a to match the one in
>> > > qrh-b)? If so, then when you press the button in the Help buffer, you
>> > > will get the error "Buffer is read-only: #<buffer Help>".
>> >
>> > > Steve Berman
>> >
>> > I did the changes and have the following
>> >
>> > (pcase (button-label button)
>> > ("[FA]"
>> > (with-help-window (help-buffer) ; Print in help buffer
>> > (insert qrh-c)))
>>
>>
>> Sure, that's a fine way to avoid the problem with the read-only state of
>> the Help buffer.
>>
>> Steve Berman
>
> I replicated the error you mentioned though.  Why does it happen ?  Is that 
> because
> the insert would be within an (with-help-window (help-buffer) ?

I get no error using the last code snippet you provided, because the
button-label is evaluated before with-help-window erases the buffer, and
with-help-window makes the *Help* buffer temporarily writeable.

Steve Berman