Modifying a variable from describe-variable

Modifying a variable from describe-variable

[Tom]

The other day I checked a variable with describe-variable (C-h v)
and I wanted to do a minor change (like changing a character) in
the value. It was a complicated variable with lots of
sublists (e.g. font-lock-keywords), so it would have been natural
and easy to change it on the spot in the *Help* buffer.

E.g. the user presses e (for edit) in the *Help* buffer which
either becomes writable or a new buffer pops up with the variable
value. The user modifies the value, presses C-c C-c and the
modifications are applied to the variable.

It does not seem hard to implement and it would be quite
convenient for quick experimenting with the value of some variable.

I checked the bindings (surely someone has thought of this
before), but I didn't find an existing function to do that.

Re: Modifying a variable from describe-variable

[Stefan Monnier]

> E.g. the user presses e (for edit) in the *Help* buffer which
> either becomes writable or a new buffer pops up with the variable
> value.  The user modifies the value, presses C-c C-c and the
> modifications are applied to the variable.

Good idea!


        Stefan

Re: Modifying a variable from describe-variable

[Ivan Andrus]

On Jan 10, 2014, at 1:16 PM, Tom <adatgyujto@gmail.com> wrote:

> The other day I checked a variable with describe-variable (C-h v)
> and I wanted to do a minor change (like changing a character) in
> the value. It was a complicated variable with lots of
> sublists (e.g. font-lock-keywords), so it would have been natural
> and easy to change it on the spot in the *Help* buffer.
> 
> E.g. the user presses e (for edit) in the *Help* buffer which
> either becomes writable or a new buffer pops up with the variable
> value. The user modifies the value, presses C-c C-c and the
> modifications are applied to the variable.
> 
> It does not seem hard to implement and it would be quite
> convenient for quick experimenting with the value of some variable.
> 
> I checked the bindings (surely someone has thought of this
> before), but I didn't find an existing function to do that.


Even simpler (to implement) would be a binding to customize-variable.  Of course, it might not always work, but might be preferable to some people in the cases when it does work.

I think the hardest part would be getting it to DTRT WRT buffer local-ness and such.

-Ivan

Re: Modifying a variable from describe-variable

[Daniel Colascione]

On 01/10/2014 08:14 PM, Ivan Andrus wrote:
> On Jan 10, 2014, at 1:16 PM, Tom <adatgyujto@gmail.com> wrote:
>
>> The other day I checked a variable with describe-variable (C-h v)
>> and I wanted to do a minor change (like changing a character) in
>> the value. It was a complicated variable with lots of
>> sublists (e.g. font-lock-keywords), so it would have been natural
>> and easy to change it on the spot in the *Help* buffer.
>>
>> E.g. the user presses e (for edit) in the *Help* buffer which
>> either becomes writable or a new buffer pops up with the variable
>> value. The user modifies the value, presses C-c C-c and the
>> modifications are applied to the variable.
>>
>> It does not seem hard to implement and it would be quite
>> convenient for quick experimenting with the value of some variable.
>>
>> I checked the bindings (surely someone has thought of this
>> before), but I didn't find an existing function to do that.
>
>
> Even simpler (to implement) would be a binding to customize-variable

XEmacs uses "c" for this purpose. We might as well too.

Re: Modifying a variable from describe-variable

[Stefan Monnier]

> Even simpler (to implement) would be a binding to customize-variable.

There should already be a button for that.


        Stefan

Re: Modifying a variable from describe-variable

[Tom]

Ivan Andrus <darthandrus <at> gmail.com> writes:
> 
> Even simpler (to implement) would be a binding to customize-variable.  Of 
course, it might not always work,
> but might be preferable to some people in the cases when it does work.

Both could be provided. c - customize and  e - edit (for advanced users).

I'd prefer editing the lisp value directly, since I never use customize
and as you also mention it does not work for all variables.

Re: Modifying a variable from describe-variable

[João Távora]

Tom <adatgyujto@gmail.com> writes:

> Ivan Andrus <darthandrus <at> gmail.com> writes:
>> 
>> Even simpler (to implement) would be a binding to customize-variable.  Of 
> course, it might not always work,
>> but might be preferable to some people in the cases when it does work.
> Both could be provided. c - customize and  e - edit (for advanced users).
> I'd prefer editing the lisp value directly, since I never use customize
> and as you also mention it does not work for all variables.

This is so good I've already hacked it for me. No idea if I'm doing it
correctly though...

Thanks a lot for the idea.

=== modified file 'lisp/help-fns.el'
--- lisp/help-fns.el	2013-12-07 17:05:38 +0000
+++ lisp/help-fns.el	2014-01-11 10:10:18 +0000
@@ -711,6 +711,15 @@
 			    version package))))))
     output))
 
+(defvar describe-described-variable nil
+  "Symbol naming the variable described by `describe-variable'")
+
+(defun describe-edit-variable ()
+  (interactive)
+  (set describe-described-variable
+       (call-interactively 'eval-expression))
+  (revert-buffer t t t))
+
 ;;;###autoload
 (defun describe-variable (variable &optional buffer frame)
   "Display the full documentation of VARIABLE (a symbol).
@@ -753,6 +762,11 @@
 	  (help-setup-xref (list #'describe-variable variable buffer)
 			   (called-interactively-p 'interactive))
 	  (with-help-window (help-buffer)
+            (setq-local describe-described-variable variable)
+            (let ((map (make-sparse-keymap)))
+              (set-keymap-parent map help-mode-map)
+              (define-key map (kbd "e") 'describe-edit-variable)
+              (use-local-map map))
 	    (with-current-buffer buffer
 	      (prin1 variable)
 	      (setq file-name (find-lisp-object-file-name variable 'defvar))

Re: Modifying a variable from describe-variable

[martin rudalics]

 > I'd prefer editing the lisp value directly, since I never use customize
 > and as you also mention it does not work for all variables.

Interesting idea.  How do you intend to ship around complications wrt
the printed representation of objects?  For example, how are you going
to handle quotes?

martin

Re: Modifying a variable from describe-variable

[David Kastrup]

martin rudalics <rudalics@gmx.at> writes:

>> I'd prefer editing the lisp value directly, since I never use customize
>> and as you also mention it does not work for all variables.
>
> Interesting idea.  How do you intend to ship around complications wrt
> the printed representation of objects?  For example, how are you going
> to handle quotes?

As long as you only read and not evaluate the expression, this should be
straightforward.

-- 
David Kastrup

Re: Modifying a variable from describe-variable

[martin rudalics]

> As long as you only read and not evaluate the expression, this should be
> straightforward.

Isn't editing and evaluating what the OP wants to do?

martin

Re: Modifying a variable from describe-variable

[David Kastrup]

martin rudalics <rudalics@gmx.at> writes:

>> As long as you only read and not evaluate the expression, this should be
>> straightforward.
>
> Isn't editing and evaluating what the OP wants to do?

My impression was that editing and _setting_ the variable was what he
wanted to do.  Evaluation would only get in the way for that.

-- 
David Kastrup

Re: Modifying a variable from describe-variable

[Tom]

João Távora <joaotavora <at> gmail.com> writes:
r all variables.
> 
> This is so good I've already hacked it for me. No idea if I'm doing it
> correctly though...
> 
> Thanks a lot for the idea.

If I understand correctly your solution does not provide the current
value of the variable by default, though this is the point.

E.g. if I have a value like


(("\\.org$" . org-mode)
 ("\\.php$" . html-mumamo-mode)
 ("\\.gpg\\(~\\|\\.~[0-9]+~\\)?\\'" nil epa-file)
 ("\\.dz\\'" nil jka-compr)
 ("\\.xz\\'" nil jka-compr)
 ("\\.lzma\\'" nil jka-compr)
 ("\\.lz\\'" nil jka-compr)
 ("\\.g?z\\'" nil jka-compr)
 ("\\.bz2\\'" nil jka-compr)
 ("\\.Z\\'" nil jka-compr)))


and I want to change a some minor thing it then I don't want to 
type whe whole thing. I'd like to have the current value displayed 
in a buffer, modify it then simply apply it.

Your solution can be useful for primitive types, but handling 
more complex values in the echo area would not be really convenient.

Re: Modifying a variable from describe-variable

[Tom]

David Kastrup <dak <at> gnu.org> writes:
> 
> My impression was that editing and _setting_ the variable was what he
> wanted to do.  Evaluation would only get in the way for that.
> 

Yes, editing and setting is preferable, so the user just sees the
lisp value in a buffer, modifies it and then presses some key to set
the variable to it.

Re: Modifying a variable from describe-variable

[João Távora]

Tom <adatgyujto@gmail.com> writes:
>> This is so good I've already hacked it for me. No idea if I'm doing it
>> correctly though...
>>
>> Thanks a lot for the idea.
>
> If I understand correctly your solution does not provide the current
> value of the variable by default, though this is the point.
> and I want to change a some minor thing it then I don't want to
> type whe whole thing. I'd like to have the current value displayed
> in a buffer, modify it then simply apply it.

I see, I see. Then I think you want "c" keybinding that someone
suggested that takes you to a customize buffer. I think that would be
the solution most integrated with emacs's solution. I didn't implement
that.

> Your solution can be useful for primitive types, but handling
> more complex values in the echo area would not be really convenient.

On the other hand, the minibuffer can do multi-line-editing, I don't
find that inconvenient.

Re: Modifying a variable from describe-variable

[Tom]

João Távora <joaotavora <at> gmail.com> writes:
> 
> I see, I see. Then I think you want "c" keybinding that someone
> suggested that takes you to a customize buffer. I think that would be
> the solution most integrated with emacs's solution. 

That's not a complete solution, because not all variables are
customizable. This feature should not be limited to only customizable
variables.

BTW, it does not seem hard to implement. One only needs to (prin1 ...)
the value to a buffer where the user can modify it and then it can
be read back with (read).

> I didn't implement that.

Another thing: buffer local variables should be handled somehow.
For example, it could be recorded from which buffer C-h v was 
called and the code should switch to that buffer temporarily and
set the variable there, so if the variable has a buffer local binding
then the local variable value is modified, not the global one.

Re: Modifying a variable from describe-variable

[Josh]

On Sat, Jan 11, 2014 at 6:34 PM, João Távora <joaotavora@gmail.com> wrote:
>> Your solution can be useful for primitive types, but handling
>> more complex values in the echo area would not be really convenient.
>
> On the other hand, the minibuffer can do multi-line-editing, I don't
> find that inconvenient.

Deepak Goel's miniedit library[0] makes such editing quite pleasant.

[0] http://www.emacswiki.org/emacs/MiniEdit

Re: Modifying a variable from describe-variable

[Stefan Monnier]

> This feature should not be limited to only customizable variables.

Agreed.

> BTW, it does not seem hard to implement.  One only needs to (prin1 ...)
> the value to a buffer where the user can modify it and then it can
> be read back with (read).

Indeed.  Tho you'll also want to pretty print it.
Maybe even better would be to make the *Help* buffer writable, mark all
the non-value text as read-only and bind C-c C-c to a new command
`help-set-variable'.

> Another thing: buffer local variables should be handled somehow.

Yes, that's very important, but not hard either.


        Stefan

Re: Modifying a variable from describe-variable

[Tom]

Stefan Monnier <monnier <at> iro.umontreal.ca> writes:
> 
> Indeed.  Tho you'll also want to pretty print it.
> Maybe even better would be to make the *Help* buffer writable, mark all
> the non-value text as read-only and bind C-c C-c to a new command
> `help-set-variable'.
> 

Using the Help buffer has the additional advantage that the user can see
the documentation of the variable while tinkering with its value.