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Re: bug#3688: Also need (auto-fill-mode nil) to trigger this bug
From: |
Alan Mackenzie |
Subject: |
Re: bug#3688: Also need (auto-fill-mode nil) to trigger this bug |
Date: |
Mon, 29 Jun 2009 21:37:11 +0000 |
User-agent: |
Mutt/1.5.9i |
Hi, Kees!
On Mon, Jun 29, 2009 at 11:18:10AM +0200, Kees Bakker wrote:
> On Monday 29 June 2009, Stefan Monnier wrote:
> > > (auto-fill-mode nil)
> > All minor modes are turned on with a positive arg and turned off with
> > a negative arg. A nil argument may toggle it, but that might change
> > in the future. A `toggle' argument toggles most (but not all) minor
> > modes.
> OK. I didn't know that (and I'm using emacs for almost two decades
> now). Still I want to express my dislike about the way a "nil" arg is
> handled.
OK, but look on the bright side - your confusion led directly to a bug
being fixed. Your discomfort for everybody's gain. Think of yourself as
a hero, not a victim. ;-)
> First, is 0 a positive arg? Some people might think so (I do).
I don't think so, and I'm a graduate mathematician. But I still remember
long unresolved discussions amongst maths people about whether zero is
positive, and sometimes terms like "strictly positive" and "non-negative"
were used. Trouble is, "strictly positive" is a bit of a mouthful, and
"non-negative" is a bit, well, negative - do we really want to describe
something by what it isn't rather than what it is?
> It is a bit confusing. (auto-fill-mode 0) will turn the mode off, so
> in that sense a zero is not a positive arg. To summarize
> (auto-fill-mode) ;;; toggles
> (auto-fill-mode 0) ;;; turn off
> (auto-fill-mode nil) ;;; toggles
> (auto-fill-mode -1) ;;; turn off
> (auto-fill-mode 1) ;;; turn on
> (auto-fill-mode t) ;;; turn on
(auto-fill-mode 0) shouldn't be troublesome to a C hacker. :-)
> Toggling for a "nil" argument does not make sense to me.
`auto-fill-mode' is also an interactive command, and as such it has an
&optional argument. The Right Thing to do with "M-x auto-fill-mode" is
to toggle. The omitted argument becomes nil, hence the the above is
(auto-fill-mode nil) in lisp. It does make sense, sort of. But I admit,
I sometimes find it confusing too.
Actually, looking at the doc string for this command:
Toggle Auto Fill mode.
With ARG, turn Auto Fill mode on if and only if ARG is positive.
In Auto Fill mode, inserting a space at a column beyond
`current-fill-column' automatically breaks the line at a previous
space.
, it is incomplete in that it doesn't specify what happens when ARG isn't
positive. Maybe this would be better:
Turn AutoFill mode on if ARG is positive, turn it off if ARG is zero
or negative, toggle it if ARG is nil (or absent).
> Kees
--
Alan Mackenzie (Nuremberg, Germany).