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Re: Keybinding Default Command and Execution with Argument

From: tomas
Subject: Re: Keybinding Default Command and Execution with Argument
Date: Thu, 5 Nov 2020 16:58:11 +0100
User-agent: Mutt/1.5.21 (2010-09-15)

On Thu, Nov 05, 2020 at 04:41:11PM +0100, Christopher Dimech wrote:
> I made a simple defun to move the current character over n other characters.
> It behaves a differently than transpose-chars, because the cursor point stays
> on the same character, rather than moving to the cursor next to the swapped
> character to the right.
> When using transpose-chars. one can use transpose-chars without any argument,
> taking the default of one.
>   M-x transpose-chars
> Alternatively, one can pass an argument (e.g. 3) as follows
>   C-u 3 M-x transpose-chars
> Currently, I can only use Skip-Over-Chars with argument.  Is there a way to
> use the function Skip-Over-Chars without requiring an argument, but defaulting
> the argument to one as what can be done with transpose-chars?

Ask `transpose-chars' itself :)

I.e. do

  C-h f transpose-chars

You'll get a small help buffer explaining transpose-chars. Basically the
function's docstring, and then something.

Part of this something is the function's location, like so:

    "transpose-chars is an interactive compiled Lisp function in
     in ‘simple.el’.

     It is bound to C-t.

     [more stuff]"

The simple.el is highlighted as a link. It is a link. If your
Emacs installation is sane, you can put point at this link
(alternatively you click on it), and you get to transpose-char's
definition, in simple.el. There you see:

  (defun transpose-chars (arg)
    "Interchange characters around point, moving forward one character.
  With prefix arg ARG, effect is to take character before point
  and drag it forward past ARG other characters (backward if ARG negative).
  If no argument and at end of line, the previous two chars are exchanged."
    (interactive "*P")
    (when (and (null arg) (eolp) (not (bobp))
          ... ) ...) ...)

So they are using (interactive "P") for that. You can look up what that
means in `interactive's documentation. The asterisk is there to ensure
that the buffer is writable.

Emacs teaches you the tricks of the Grandmasters ;-)

 - t

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