Re: align mysteries

[Eli Zaretskii]

> From: Lars Ingebrigtsen <larsi@gnus.org>
> Date: Thu, 14 Oct 2021 23:41:44 +0200
> Cc: dick <dick.r.chiang@gmail.com>, emacs-devel@gnu.org
> 
> Lars Ingebrigtsen <larsi@gnus.org> writes:
> 
> > But...  why?  Why only have `M-x align' do something in text modes if
> > you give it a prefix?
> 
> It's to be able to have different predefined alignments depending on the
> prefix, I guess:
> 
>     ;; With a numeric prefix argument, or C-u, space delimited text
>     ;; tables will be aligned.
>     (text-column
>      (regexp   . "\\(^\\|\\S-\\)\\([ \t]+\\)\\(\\S-\\|$\\)")
>      (group    . 2)
>      (modes    . align-text-modes)
>      (repeat   . t)
>      (run-if   . ,(lambda ()
>                     (and current-prefix-arg
>                          (not (eq '- current-prefix-arg))))))
> 
>     ;; With a negative prefix argument, lists of dollar figures will
>     ;; be aligned.
>     (text-dollar-figure
>      (regexp   . "\\$?\\(\\s-+[0-9]+\\)\\.")
>      (modes    . align-text-modes)
>      (justify  . t)
>      (run-if   . ,(lambda ()
>                     (eq '- current-prefix-arg))))
> 
> It still doesn't explain why the first one doesn't just test that it's
> not minus.

It really doesn't make sense to have this discussion without involving
John Wiegley, the author (CC'ed).

> The `align' doc string should mention that the prefix can influence
> which rule is used, at the very least.

The doc string needs a lot of work, but it cannot be improved before
we understand well enough what the function is doing in the various
use cases.