RE: prefix arg when mouse clicking on header

["Drew Adams" <drew.adams@oracle.com>]

> I have some difficulties with the command proced-sort-header in
> proced.el. This command is called when the mouse is on the header
> line. The first arg of this command is the mouse event. I'd like to
> give the command an optional prefix arg. But somehow it seems to me
> that clicking on the header line is different from clicking
> elsewhere. What is the proper way to access the prefix arg when
> clicking on the header line?
> 
> I used to have (interactive "e\nP"), but that ignores the prefix arg.
> 
> Instead of "P", I really would like to have something like
> 
> (interactive (list last-input-event (or current-prefix-arg 'no-arg)))
> 
> (The 'no-arg is similar to 'toggle in define-derived-mode.) 
> But again, this ignores the prefix arg. By trial an error I have
> found that
> 
> (interactive (list last-input-event (or last-prefix-arg 'no-arg)))
> 
> seems to work. But is this the right thing? Why last-prefix-arg
> instead of current-prefix-arg? Certainly, this is consistent with
> the code letter P being ignored by interactive.
> 
> Also I was wondering what is the proper replacement for the code
> letter e used by interactive when the list is constructed by hand.
> last-input-event is used in commands like Buffer-menu-sort-by-column.
> Is last-input-event always equivalent to the code letter e?
> If yes, that could go into the elisp manual. If not, what would be
> the proper replacement?

(interactive "e\nP") works for me.

For example, try the version of `mouse-yank-secondary' in `mouse+.el', with
`second-sel.el' also loaded. If `mouse-yank-secondary' is bound to, say,
`M-mouse-2', then `C-u 3 M-mouse-2' yanks the 3rd most recent secondary
selection.

The code for that, as an example, is here:
http://www.emacswiki.org/emacs/mouse%2b.el ; mouse+.el
http://www.emacswiki.org/emacs/second-sel.el