prefix-region

prefix-region

[Hrvoje Niksic]

I have found this function, originally from XEmacs, immensely useful:

    (prefix-region PREFIX)

    Insert PREFIX at the beginning of each line between mark and point.

It is useful for all kinds of editing jobs, including commenting out
pieces of code and quoting mail.  While some of these things can be
achieved using other Emacs functions, `M-x prefix-region' is often
much more convenient, especially when the more sophisticated
mechanisms are unavailable (such as when editing snippets of code in
mail messages).

This function is not as easy to write as it seems because there are
several corner cases that need to be gotten right (empty region,
whether mark precedes point or vice versa, mark/point at line start or
end positions).  Because of that I propose that you include the
function in Emacs.

I wasn't satisfied with the XEmacs implementation of this function so
I wrote and tested this one:

(defun prefix-region (prefix)
  "Insert PREFIX at the beginning of each line between mark and point."
  (interactive "sPrefix string: ")
  (let ((end (region-end)))
    (save-excursion
      (goto-char (region-beginning))
      (beginning-of-line)
      (save-restriction
	(narrow-to-region (point) end)
	(while (not (eobp))
	  (insert prefix)
	  (forward-line 1))))))

Re: prefix-region

[Andreas Schwab]

Hrvoje Niksic <hniksic@xemacs.org> writes:

> I have found this function, originally from XEmacs, immensely useful:
>
>     (prefix-region PREFIX)
>
>     Insert PREFIX at the beginning of each line between mark and point.

Looks like string-rectangle can do the same, and more.

Andreas.

-- 
Andreas Schwab, SuSE Labs, schwab@suse.de
SuSE Linux Products GmbH, Maxfeldstraße 5, 90409 Nürnberg, Germany
Key fingerprint = 58CA 54C7 6D53 942B 1756  01D3 44D5 214B 8276 4ED5
"And now for something completely different."

Re: prefix-region

[Hrvoje Niksic]

Andreas Schwab <schwab@suse.de> writes:

> Hrvoje Niksic <hniksic@xemacs.org> writes:
>
>> I have found this function, originally from XEmacs, immensely useful:
>>
>>     (prefix-region PREFIX)
>>
>>     Insert PREFIX at the beginning of each line between mark and point.
>
> Looks like string-rectangle can do the same, and more.

That behaves very differently when the endpoints of the region aren't
at line beginnings.  It also prefixes the last line even if it wasn't
really part of the selection.

Re: prefix-region

[Romain Francoise]

Hrvoje Niksic <hniksic@xemacs.org> writes:

>> Looks like string-rectangle can do the same, and more.

> That behaves very differently when the endpoints of the region aren't
> at line beginnings.  It also prefixes the last line even if it wasn't
> really part of the selection.

See also `string-insert-rectangle'.

-- 
Romain Francoise <romain@orebokech.com> | I've become someone else's
it's a miracle -- http://orebokech.com/ | nightmare...

Re: prefix-region

[Hrvoje Niksic]

Romain Francoise <romain@orebokech.com> writes:

> See also `string-insert-rectangle'.

That's still a "rectangle" function, not a "region" function, which is
why it gets the corner cases wrong in exactly the same way that
`string-rectangle' does.

I'm not saying that there is anything wrong with those functions, only
that they are not as useful for this particular purpose as
`prefix-region' is.

Re: prefix-region

[Miles Bader]

2005/10/25, Hrvoje Niksic <hniksic@xemacs.org>:
> I'm not saying that there is anything wrong with those functions, only
> that they are not as useful for this particular purpose as
> `prefix-region' is.

Which purpose though?  I suspect 90% of the time, `comment-dwim' (M-;)
or `indent-rigidly' are really what's wanted, and do the job better
(for instance `comment-dwim' handles mail quoting and commenting-out
of code just about perfectly); adding arbitrary prefixes seems kinda
rare.

-Miles
--
Do not taunt Happy Fun Ball.

Re: prefix-region

[Hrvoje Niksic]

Miles Bader <snogglethorpe@gmail.com> writes:

> 2005/10/25, Hrvoje Niksic <hniksic@xemacs.org>:
>> I'm not saying that there is anything wrong with those functions, only
>> that they are not as useful for this particular purpose as
>> `prefix-region' is.
>
> Which purpose though?

Prefixing a region with an arbitrary string.  It comes up a lot.

> I suspect 90% of the time, `comment-dwim' (M-;)

It won't work when editing snippets of code in mail messages or when
editing a language for which you don't have a major mode handy.

> or `indent-rigidly' are really what's wanted, and do the job better
> (for instance `comment-dwim' handles mail quoting and commenting-out
> of code just about perfectly); adding arbitrary prefixes seems kinda
> rare.

I don't think it's all that rare.  I've used the function a lot over
the years, and I know other XEmacs users who have found it useful.
Writing a replacement one is non-trivial.

Re: prefix-region

[Stefan Monnier]

>> or `indent-rigidly' are really what's wanted, and do the job better
>> (for instance `comment-dwim' handles mail quoting and commenting-out
>> of code just about perfectly); adding arbitrary prefixes seems kinda
>> rare.

> I don't think it's all that rare.

Agreed: I'd guess that about 80% of my uses of string-rectangle would be
covered by prefix-region.  OTOH since I'm used to string-rectangle,
I probably wouldn't bother to use prefix-region.
(I've even found myself using string-rectangle instead of M-;)


        Stefan

Re: prefix-region

[Romain Francoise]

I think it could be useful, even if other functions can do the job in
different ways.  If Richard doesn't want it as a default command, we
could install it in misc.el for people who want it.

-- 
Romain Francoise <romain@orebokech.com> | I like the streets when
it's a miracle -- http://orebokech.com/ | they're empty, I can make the
                                        | rest up.

Re: prefix-region

[Edward O'Connor]

> Agreed: I'd guess that about 80% of my uses of string-rectangle would be
> covered by prefix-region.  OTOH since I'm used to string-rectangle,
> I probably wouldn't bother to use prefix-region.
> (I've even found myself using string-rectangle instead of M-;)

Same here.

-- 
Edward O'Connor
hober0@gmail.com

Ense petit placidam sub libertate quietem.

Re: prefix-region

[Andreas Schwab]

Hrvoje Niksic <hniksic@xemacs.org> writes:

> Miles Bader <snogglethorpe@gmail.com> writes:
>
>> 2005/10/25, Hrvoje Niksic <hniksic@xemacs.org>:
>>> I'm not saying that there is anything wrong with those functions, only
>>> that they are not as useful for this particular purpose as
>>> `prefix-region' is.
>>
>> Which purpose though?
>
> Prefixing a region with an arbitrary string.  It comes up a lot.

I have yet to find a situation where string-rectangle did not suit my
needs.  YMMV, of course.

Andreas.

-- 
Andreas Schwab, SuSE Labs, schwab@suse.de
SuSE Linux Products GmbH, Maxfeldstraße 5, 90409 Nürnberg, Germany
Key fingerprint = 58CA 54C7 6D53 942B 1756  01D3 44D5 214B 8276 4ED5
"And now for something completely different."

Re: prefix-region

[Hrvoje Niksic]

Andreas Schwab <schwab@suse.de> writes:

>> Prefixing a region with an arbitrary string.  It comes up a lot.
>
> I have yet to find a situation where string-rectangle did not suit
> my needs.  YMMV, of course.

No one is claiming that prefix-region can do something that
string-rectangle cannot do if you are careful enough.  I do claim that
prefix-region is much more convenient to use because you don't need to
adjust region endpoints to beginning of line.

prefix-region is also more easily discovered by someone trying to,
well, prefix a region...  Before discovering it I used to do things
like `C-u M-| sed 's/^/PREFIX/'.

Re: prefix-region

[Richard M. Stallman]

It seems possibly useful, and harmless to add.
Could you write patches to the Emacs Manual and etc/NEWS
to document it?  We can't install it without that.

Re: prefix-region

[Hrvoje Niksic]

"Richard M. Stallman" <rms@gnu.org> writes:

> It seems possibly useful, and harmless to add.  Could you write
> patches to the Emacs Manual and etc/NEWS to document it?  We can't
> install it without that.

Fair enough.  I'll do that.