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Re: invisible
From: |
martin rudalics |
Subject: |
Re: invisible |
Date: |
Wed, 28 Nov 2007 23:41:23 +0100 |
User-agent: |
Mozilla Thunderbird 1.0 (Windows/20041206) |
> But how are lines and columns counted? Does an invisible newline cause
> the intended column numbersto fall back to 0? Does an invisible "a"
> cause the intended column numnber to stay put or to be incremented by 1?
We are talking about the default `line-move-ignore-invisible' t case, I
presume. `col' is the column to move to (presumably the `goal-column'
but I didn't check this). This code starts with
(move-to-column col)
and the first question is whether we can find a case where this fails to
DTRT. Apparently it might fail in the case
(when (and (not (bolp)) (invisible-p (1- (point))))
which raises the question whether `move-to-column' would move to a
position following invisible text. As I know now it does so iff that
text has a rear-nonsticky property (but I don't know about overlays).
Next our code goes into a loop
(while (and (not (eobp)) (invisible-p (point)))
(goto-char (next-char-property-change (point))))
which just skips invisible text and we can conclude that lines are _not_
counted. Moreover, it's strange that `move-to-column' didn't skip that
invisible text as well, but maybe it's a newline. The following piece
of code is contrived and I leave it as an exercise to anyone interested
to find out what it's intended to do:
(if (> (current-column) normal-column)
;; We have made some progress towards the desired column.
;; See if we can make any further progress.
(line-move-to-column (+ (current-column) (- col normal-column)))
This must have been the motivation to splice out `line-move-to-column'
back in 2001 - make it callable recursively. I don't understand the ">"
here (`normal-column' is the column `move-to-column' moved to before).
And I completely fail to understand the argument calculation: Suppose
the desired `col' is 17 and `move-to-column' moved to column 14 on that
line because everything after 14 was invisible. Also suppose the
invisible text ends at the end of some line hence `current-column' would
report 0 - or can you imagine `current-column' to report anything but
zero in this case? Now should we move to column 3 here - or what am I
missing?
The else part goes as
(goto-char normal-location)
(let ((line-beg (line-beginning-position)))
(while (and (not (bolp)) (invisible-p (1- (point))))
(goto-char
(previous-char-property-change (point) line-beg))))))))
which simply moves to the first visible position on the line where
`move-to-column' stopped. IIUC `move-to-column' never stops at a
position following invisible text unless it's rear-nonsticky, hence this
loop would be needed only to handle that special case.
All this got you is more questions asked than answered :-(
- Re: invisible, (continued)
- Re: invisible, Stefan Monnier, 2007/11/25
- Re: invisible, martin rudalics, 2007/11/26
- Re: invisible, Stefan Monnier, 2007/11/26
- Re: invisible, martin rudalics, 2007/11/26
- Re: invisible, Stefan Monnier, 2007/11/26
- Re: invisible, martin rudalics, 2007/11/27
- Re: invisible, martin rudalics, 2007/11/27
- Re: invisible, Stefan Monnier, 2007/11/27
- Re: invisible, martin rudalics, 2007/11/28
- Re: invisible, Stefan Monnier, 2007/11/28
- Re: invisible,
martin rudalics <=
- Re: invisible, Stephen Berman, 2007/11/28
- Re: invisible, martin rudalics, 2007/11/29
- Re: invisible, Stefan Monnier, 2007/11/29
- Re: invisible, Richard Stallman, 2007/11/28
- Re: invisible, martin rudalics, 2007/11/29
- Re: invisible, Stefan Monnier, 2007/11/29
- Re: invisible, martin rudalics, 2007/11/29
- Re: invisible, Stefan Monnier, 2007/11/29
- Re: invisible, martin rudalics, 2007/11/29
- Re: invisible, martin rudalics, 2007/11/30