Alt-v behavior near beginning of buffer

Alt-v behavior near beginning of buffer

[Matthew Flaschen]

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I am trying to figure out how to create a new function that will scroll
up a screen if possible, or go the beginning of the buffer otherwise; I
would then bind this to M-v.  Ultimately, I want to have the corollary
behavior for C-v.

I can't figure out how to test whether it is possible to scroll up/down
an entire screen.  I found (goto-char (point-min/max)) , so that part
should be okay.

Matthew


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Re: Alt-v behavior near beginning of buffer

[Kevin Rodgers]

Matthew Flaschen wrote:
> I am trying to figure out how to create a new function that will scroll
> up a screen if possible, or go the beginning of the buffer otherwise; I
> would then bind this to M-v.  Ultimately, I want to have the corollary
> behavior for C-v.
> 
> I can't figure out how to test whether it is possible to scroll up/down
> an entire screen.  I found (goto-char (point-min/max)) , so that part
> should be okay.

(if (pos-visible-in-window-p (point-min))
     (beginning-of-buffer)
   (scroll-down))

-- 
Kevin Rodgers
Denver, Colorado, USA

Re: Alt-v behavior near beginning of buffer

[Matthew Flaschen]

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Kevin Rodgers wrote:
> Matthew Flaschen wrote:
>> I am trying to figure out how to create a new function that will scroll
>> up a screen if possible, or go the beginning of the buffer otherwise; I
>> would then bind this to M-v.  Ultimately, I want to have the corollary
>> behavior for C-v.
>>
>> I can't figure out how to test whether it is possible to scroll up/down
>> an entire screen.  I found (goto-char (point-min/max)) , so that part
>> should be okay.
> 
> (if (pos-visible-in-window-p (point-min))
>     (beginning-of-buffer)
>   (scroll-down))
> 

Thanks, that was what I needed.  I ended up with:

(defun power-top ()
"Scrolls up a screen if possible, or goes to the top of the buffer"
(interactive)
(if (pos-visible-in-window-p (point-min))
    (goto-char (point-min))
  (scroll-down)))

(defun power-bottom ()
"Scrolls up a screen if possible, or goes to the top of the buffer"
(interactive)
(if (pos-visible-in-window-p (point-max))
    (goto-char (point-max))
  (scroll-up)))

(global-set-key [?\M-v] 'power-top )
(global-set-key [?\C-v] 'power-bottom )


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Re: Alt-v behavior near beginning of buffer

[Matthew Flaschen]

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Matthew Flaschen wrote:
> 
> (defun power-bottom ()
> "Scrolls up a screen if possible, or goes to the top of the buffer"
Doc here should be:

"Scrolls down a screen if possible, or goes to the bottom of the buffer.


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Re: Alt-v behavior near beginning of buffer

[Matthew Flaschen]

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Matthew Flaschen wrote:
> Matthew Flaschen wrote:
>> (defun power-bottom ()
>> "Scrolls up a screen if possible, or goes to the top of the buffer"
> Doc here should be:
> 
> "Scrolls down a screen if possible, or goes to the bottom of the buffer.

I wanted it to go to the beginning of the line either way, so I changed
it to:

(defun power-bottom ()
"Scrolls down a screen if possible, or goes to the bottom of the buffer"
(interactive)
(if (pos-visible-in-window-p (point-max))
    ((lambda()
       (goto-char (point-max))
       (beginning-of-line)))
  (scroll-up)))

That lambda syntax took me a while to grasp.  Is there any easier way to
do this, short of creating a function just for the lambda?

Matthew Flaschen


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Re: Alt-v behavior near beginning of buffer

[Kevin Rodgers]

Matthew Flaschen wrote:
> I wanted it to go to the beginning of the line either way, so I changed
> it to:
> 
> (defun power-bottom ()
> "Scrolls down a screen if possible, or goes to the bottom of the buffer"
> (interactive)
> (if (pos-visible-in-window-p (point-max))
>     ((lambda()
>        (goto-char (point-max))
>        (beginning-of-line)))
>   (scroll-up)))
> 
> That lambda syntax took me a while to grasp.  Is there any easier way to
> do this, short of creating a function just for the lambda?

Of course:

     (progn
       (goto-char (point-max))
       (beginning-of-line))

A good Emacs Lisp exercise would be to allow your new command to accept
a prefix argument just like scroll-up does, and pass it to scroll-up.

-- 
Kevin Rodgers
Denver, Colorado, USA

Re: Alt-v behavior near beginning of buffer

[Matthew Flaschen]

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Kevin Rodgers wrote:
> Matthew Flaschen wrote:
>> I wanted it to go to the beginning of the line either way, so I changed
>> it to:
>>
>> (defun power-bottom ()
>> "Scrolls down a screen if possible, or goes to the bottom of the buffer"
>> (interactive)
>> (if (pos-visible-in-window-p (point-max))
>>     ((lambda()
>>        (goto-char (point-max))
>>        (beginning-of-line)))
>>   (scroll-up)))
>>
>> That lambda syntax took me a while to grasp.  Is there any easier way to
>> do this, short of creating a function just for the lambda?
> 
> Of course:
> 
>     (progn
>       (goto-char (point-max))
>       (beginning-of-line))

Thanks, that's a bit simpler.  I'd seen that command before, but forgot
it (and probably never really understood what it did).

> 
> A good Emacs Lisp exercise would be to allow your new command to accept
> a prefix argument just like scroll-up does, and pass it to scroll-up.

I may do that at some point.

Matt Flaschen



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Re: Alt-v behavior near beginning of buffer

[Kevin Rodgers]

Matthew Flaschen wrote:
> Kevin Rodgers wrote:
>>     (progn
>>       (goto-char (point-max))
>>       (beginning-of-line))
> 
> Thanks, that's a bit simpler.  I'd seen that command before, but forgot
> it (and probably never really understood what it did).

<pedantic>
progn is technically not a command, which is a function with an
interactive form at the beginning of its body (optionally preceded by a
doc string).  progn is actually a special form, which is a primitive
function (i.e. implemented in C) whose arguments are not evaluated 
before being passed to the function: instead, the special form is 
responsible for evaluating them as desired.

See the "Function Type", "Primitive Function Type", "Special Forms", and
"Defining Commands" nodes of the Emacs Lisp manual.
</pedantic>

-- 
Kevin Rodgers
Denver, Colorado, USA

Re: Alt-v behavior near beginning of buffer

[Matthew Flaschen]

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Kevin Rodgers wrote:
> Matthew Flaschen wrote:
>> Kevin Rodgers wrote:
>>>     (progn
>>>       (goto-char (point-max))
>>>       (beginning-of-line))
>>
>> Thanks, that's a bit simpler.  I'd seen that command before, but forgot
>> it (and probably never really understood what it did).
> 
> <pedantic>
> progn is technically not a command, which is a function with an
> interactive form at the beginning of its body (optionally preceded by a
> doc string).  progn is actually a special form, which is a primitive
> function (i.e. implemented in C) whose arguments are not evaluated
> before being passed to the function: instead, the special form is
> responsible for evaluating them as desired.
> 
> See the "Function Type", "Primitive Function Type", "Special Forms", and
> "Defining Commands" nodes of the Emacs Lisp manual.
> </pedantic>

Thanks for clarifying.  I'm still trying to get the feel of emacs lisp
(off and on).

Matthew Flaschen


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Re: Alt-v behavior near beginning of buffer

[Kevin Rodgers]

Matthew Flaschen wrote:
> Matthew Flaschen wrote:
>> (defun power-bottom ()
>> "Scrolls up a screen if possible, or goes to the top of the buffer"
> Doc here should be:
> 
> "Scrolls down a screen if possible, or goes to the bottom of the buffer.

Or to use Emacs terminology:

"Scroll text of current window upward, or move point near end of buffer.

The window text is scrolled unless the end of the buffer is visible;
otherwise point is moved to beginning of the last line of the buffer."

-- 
Kevin Rodgers
Denver, Colorado, USA

Re: Alt-v behavior near beginning of buffer

[Matthew Flaschen]

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Kevin Rodgers wrote:
> Matthew Flaschen wrote:
>> Matthew Flaschen wrote:
>>> (defun power-bottom ()
>>> "Scrolls up a screen if possible, or goes to the top of the buffer"
>> Doc here should be:
>>
>> "Scrolls down a screen if possible, or goes to the bottom of the buffer.
> 
> Or to use Emacs terminology:
> 
> "Scroll text of current window upward, or move point near end of buffer.
> 
> The window text is scrolled unless the end of the buffer is visible;
> otherwise point is moved to beginning of the last line of the buffer."
> 

Thanks, I've adapted this for the other function too.

Matt Flaschen


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Re: Alt-v behavior near beginning of buffer

[Eric Eide]

"Matthew" == Matthew Flaschen <matthew.flaschen@gatech.edu> writes:

	Matthew> I am trying to figure out how to create a new function that
	Matthew> will scroll up a screen if possible, or go the beginning of
	Matthew> the buffer otherwise; I would then bind this to M-v.
	Matthew> Ultimately, I want to have the corollary behavior for C-v.

If you want an Emacs add-on that does this (and much more), you might try:

	http://www.cs.utah.edu/~eeide/emacs/scroll-in-place.el.gz

Eric.

-- 
-------------------------------------------------------------------------------
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http://www.cs.utah.edu/~eeide/ . +1 (801) 585-5512 voice, +1 (801) 581-5843 FAX

Re: Alt-v behavior near beginning of buffer

[Matthew Flaschen]

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Eric Eide wrote:
> "Matthew" == Matthew Flaschen <matthew.flaschen@gatech.edu> writes:
> 
> 	Matthew> I am trying to figure out how to create a new function that
> 	Matthew> will scroll up a screen if possible, or go the beginning of
> 	Matthew> the buffer otherwise; I would then bind this to M-v.
> 	Matthew> Ultimately, I want to have the corollary behavior for C-v.
> 
> If you want an Emacs add-on that does this (and much more), you might try:
> 
> 	http://www.cs.utah.edu/~eeide/emacs/scroll-in-place.el.gz
> 
> Eric.
> 

Sometimes I think it's impossible to do anything in emacs without
reinventing the wheel. ;)  However, the package seems a bit hefty, given
that the emacs scrolling behavior (after my adjustment) doesn't really
bother me.  I'll hold off installing it for now, but may do so later.

Thanks,

Matt


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