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Fixing rectangle operations

From: Herbert Euler
Subject: Fixing rectangle operations
Date: Thu, 15 Dec 2005 12:41:53 +0800

Hello everyone,

Both Emacs and Vim support operate on a rectangle
region in buffer, but I think Vim handles it better. The
following example comes from Vim Main Help File.
Assume the content one want to insert 'very ' before

   This is a -!-long line
   Any other long line

The point is before 'long' in the first line. Vim documents
that if one want to insert 'very ' before these two 'long's,
it will ignore the short line. Hence the result is:

   This is a very long line
   Any other very long line

I tested this in Emacs. I set a mark at where the point
is in the orignal text, and move the point to the third
line, before 'long'. But M-x string-insert-rectangle yields:

   This is a very long line
   short     very
   Any other very long line

This is not good.

Still, I don't think this is what I mean in most conditions,
and prefer leaving short lines as what they were.
I modified 'rect.el' so that rectangle operations will
not operate on short lines. The only function needs to
be changed is 'apply-on-rectangle'. I just add the
verification of whether the rectangle covers short

   ;; The replacement for `operate-on-rectangle' -- dv
   (defun apply-on-rectangle (function start end &rest args)
     "Call FUNCTION for each line of rectangle with corners at START, END.
   FUNCTION is called with two arguments: the start and end columns of the
rectangle, plus ARGS extra arguments. Point is at the beginning of line when
   the function is called."
     (let (startcol startpt endcol endpt)
         (goto-char start)
         (setq startcol (current-column))
         (setq startpt (point))
         (goto-char end)
         (setq endcol (current-column))
         (forward-line 1)
         (setq endpt (point-marker))
         ;; ensure the start column is the left one.
         (if (< endcol startcol)
              (let ((col startcol))
                (setq startcol endcol endcol col)))
         ;; start looping over lines
         (goto-char startpt)
         (while (< (point) endpt)
(end-of-line) ; first go to end of each line (if (>= (current-column) start) ; this simple test will avoid operating on short lines
                (apply function startcol endcol args))
            (forward-line 1)))

I think this is better than what Emacs does now.

Guanpeng Xu

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