How to create new buffer with t-m-m active region?

How to create new buffer with t-m-m active region?

[Dan Davison]

How would I generate a new buffer containing an active region such that
the next command issued in the new buffer will act on the region? (And
so that the region is highlighted)

For example, this function doesn't do what it wants to do:

(defun new-buffer-w-active-region ()
  (interactive)
  (let ((transient-mark-mode t))
    (switch-to-buffer (get-buffer-create "region-test"))
    (delete-region (point-min) (point-max))
    (insert "I want these lines\n")
    (insert "to be in an active region with t-m-m on\n")
    (insert "such that comment-region comments them out\n")
    (emacs-lisp-mode)
    (push-mark (point-min) nil 'activate)))


With that function, the following doesn't do what is intended:

M-x new-buffer-w-active-region
M-;

Thanks,

Dan

Re: How to create new buffer with t-m-m active region?

[Stefan Monnier]

> (defun new-buffer-w-active-region ()
>   (interactive)
>   (let ((transient-mark-mode t))
>     (switch-to-buffer (get-buffer-create "region-test"))
>     (delete-region (point-min) (point-max))
>     (insert "I want these lines\n")
>     (insert "to be in an active region with t-m-m on\n")
>     (insert "such that comment-region comments them out\n")
>     (emacs-lisp-mode)
>     (push-mark (point-min) nil 'activate)))

You need to wrap the delete-region and the inserts with (let
((deactivate-mark)) ...) so that they don't cause the mark to be
deactivated as soon as the command ends.


        Stefan

RE: How to create new buffer with t-m-m active region?

[Drew Adams]

> How would I generate a new buffer containing an active region 
> such that the next command issued in the new buffer will act
> on the region? (And so that the region is highlighted)
> 
> For example, this function doesn't do what it wants to do:
> 
> (defun new-buffer-w-active-region ()
>   (interactive)
>   (let ((transient-mark-mode t))
>     (switch-to-buffer (get-buffer-create "region-test"))
>     (delete-region (point-min) (point-max))
>     (insert "I want these lines\n")
>     (insert "to be in an active region with t-m-m on\n")
>     (insert "such that comment-region comments them out\n")
>     (emacs-lisp-mode)
>     (push-mark (point-min) nil 'activate)))
> 
> 
> With that function, the following doesn't do what is intended:
> 
> M-x new-buffer-w-active-region
> M-;

Yes, this is a common gotcha that you just have to learn once if you do this
kind of thing: Add this sexp at the end of your command:

(setq deactivate-mark  nil)

Re: How to create new buffer with t-m-m active region?

[Dan Davison]

"Drew Adams" <drew.adams@oracle.com> writes:

>> How would I generate a new buffer containing an active region 
>> such that the next command issued in the new buffer will act
>> on the region? (And so that the region is highlighted)
>> 
>> For example, this function doesn't do what it wants to do:
>> 
>> (defun new-buffer-w-active-region ()
>>   (interactive)
>>   (let ((transient-mark-mode t))
>>     (switch-to-buffer (get-buffer-create "region-test"))
>>     (delete-region (point-min) (point-max))
>>     (insert "I want these lines\n")
>>     (insert "to be in an active region with t-m-m on\n")
>>     (insert "such that comment-region comments them out\n")
>>     (emacs-lisp-mode)
>>     (push-mark (point-min) nil 'activate)))
>> 
>> 
>> With that function, the following doesn't do what is intended:
>> 
>> M-x new-buffer-w-active-region
>> M-;
>
> Yes, this is a common gotcha that you just have to learn once if you do this
> kind of thing: Add this sexp at the end of your command:
>
> (setq deactivate-mark  nil)

Thanks for that Drew.

Dan