bug#4102: 23.1.50; recentf-mode nil but toggles

bug#4102: 23.1.50; recentf-mode nil but toggles

[Xah Lee]

gosh, stung by this bug.

in my elisp code, i have:

 (recentf-mode nil)

this should turn it off, but actually it toggles.

here's a quote of its inline doc:
«
(recentf-mode &optional arg)

Toggle recentf mode.
With prefix argument arg, turn on if positive, otherwise off.
»

this is reproduciable in the following:

GNU Emacs 23.1.1 (i386-mingw-nt6.0.6002) of 2009-07-29 on SOFT-MJASON

GNU Emacs 23.1.50.1 (i386-mingw-nt6.0.6002) of 2009-06-30 on LENNART-69DE564 
(patched)

  Xah
∑ http://xahlee.org/

☄

bug#4102: 23.1.50; recentf-mode nil but toggles

[Stefan Monnier]

> in my elisp code, i have:
> (recentf-mode nil)
> this should turn it off, but actually it toggles.

That's indeed the standard behavior for all minor modes.  Use integers
to avoid such surprises.

> With prefix argument arg, turn on if positive, otherwise off.

It's not clear whether nil is positive or negative.


        Stefan

bug#4102: 23.1.50; recentf-mode nil but toggles

[Xah Lee]

>> With prefix argument arg, turn on if positive, otherwise off.
>
> It's not clear whether nil is positive or negative.

Thanks. That's interesting.

Can the doc adds a warning like:

The argument should be a integer. Do not use t or nil.

?

  Xah
∑ http://xahlee.org/

☄

----- Original Message ----- 
From: "Stefan Monnier" <monnier@iro.umontreal.ca>
To: "Xah Lee" <xah@xahlee.org>
Cc: <4102@emacsbugs.donarmstrong.com>; <bug-gnu-emacs@gnu.org>
Sent: Monday, August 10, 2009 9:40 AM
Subject: Re: bug#4102: 23.1.50; recentf-mode nil but toggles


>> in my elisp code, i have:
>> (recentf-mode nil)
>> this should turn it off, but actually it toggles.
>
> That's indeed the standard behavior for all minor modes.  Use integers
> to avoid such surprises.
>
>> With prefix argument arg, turn on if positive, otherwise off.
>
> It's not clear whether nil is positive or negative.

bug#4102: 23.1.50; recentf-mode nil but toggles

[Kevin Rodgers]

Xah Lee wrote:
>>> With prefix argument arg, turn on if positive, otherwise off.
>>
>> It's not clear whether nil is positive or negative.

It seems clear to me that nil is not positive, so the "otherwise"
condition holds.

> Thanks. That's interesting.
> 
> Can the doc adds a warning like:
> 
> The argument should be a integer. Do not use t or nil.

Do not use `supercalifragilisticexpialidocious' either.

How about: Use nil to toggle the mode on or off.

-- 
Kevin Rodgers
Denver, Colorado, USA

bug#4102: 23.1.50; recentf-mode nil but toggles

[Stefan Monnier]

> Do not use `supercalifragilisticexpialidocious' either.
> How about: Use nil to toggle the mode on or off.

Actually, the docstring already says that nil toggles.  If you remember
that the docstring is written here to describe the command rather than
the function, then you'll immediately conclude that

  With prefix argument arg, turn on if positive, otherwise off.

only applies when there's a prefix argument, so when there isn't, arg is
necessarily nil and the normal behavior (described on the previous line:

   Toggle recentf mode.

) applies.


        Stefan

Re: bug#4102: 23.1.50; recentf-mode nil but toggles

[Xah Lee]

On Aug 11, 9:05 pm, Kevin Rodgers <kevin.d.rodg...@gmail.com> wrote:
> Xah Lee wrote:
> >>> With prefix argument arg, turn on if positive, otherwise off.
>
> >> It's not clear whether nil is positive or negative.
>
> It seems clear to me that nil is not positive, so the "otherwise"
> condition holds.
>
> > Thanks. That's interesting.
>
> > Can the doc adds a warning like:
>
> > The argument should be a integer. Do not use t or nil.
>
> Do not use `supercalifragilisticexpialidocious' either.
>
> How about: Use nil to toggle the mode on or off.

hi Kevin,

i think that's a bit unreasonable.

the use of 1 and 0 for on and off for minor mode function, is not
exactly intuitive, because in elisp, although the lang does not have
boolean datatype, but by convention, t is for true, and nil for false,
and technically, nil is false, everything else is true.

So, minor modes using 1 and 0 is kinda unclean, un-elegant, or counter
intuitive. The reason it does that, is of course due to the fact that
emacs commands thru interactive use by convention takes universal-
argument, and universal-argument only take integer as arguments, not
some string or lisp symbol. So, there's the justification for 1 and 0.

However, in lisp code, it is also reasonable to expect that nil would
be equivalent to 0, as by lisp convention. This logic may not look
logical to you, but i think is reasonable alternative expectation.
When a mode gets its arg thru interactive use, the arg is expected to
be integers by the way emacs do things interactively, and thus
positive int is considered true or turn on, negative is considered
false/off. But in lisp code, besides 1 and 0, you can also specify t
and nil as usual by lisp convention. This could easily be considered
as a alternative design decision.

(adding to the mess is that some command will change behavior as kinda
on/off or true/false depending on whether universal-argument is called
regardless of its argument)

all things considered, i think it is reasonable that a average lisp
coder will be confused by this. Thus my recommendation that a warning
or notes be added to the doc. Is there somewhere in elisp manual that
explicitly explains/warns that commands that turn minor mode on/off
stick to 1 and 0 and consider t and nil not acceptable argument?

PS i didn't receive your previous email, i just happened to see your
reply in google group. I'm not much in the emacs dev community so i'm
not regular gnu emacs bug database reader... please cc me too on this.
thanks.

  Xah
∑ http://xahlee.org/

☄

bug#4102: 23.1.50; recentf-mode nil but toggles

[Drew Adams]

> Is there somewhere in elisp manual that
> explicitly explains/warns that commands that turn minor mode on/off
> stick to 1 and 0 and consider t and nil not acceptable argument?

(elisp) Minor Mode Conventions:

   * Define a command whose name is the same as the mode variable.  Its
     job is to enable and disable the mode by setting the variable.

     The command should accept one optional argument.  If the argument
     is `nil', it should toggle the mode (turn it on if it is off, and
     off if it is on).  It should turn the mode on if the argument is a
     positive integer, the symbol `t', or a list whose CAR is one of
     those.  It should turn the mode off if the argument is a negative
     integer or zero, the symbol `-', or a list whose CAR is a negative
     integer or zero.  The meaning of other arguments is not specified.

     Here is an example taken from the definition of
     `transient-mark-mode'.  It shows the use of `transient-mark-mode'
     as a variable that enables or disables the mode's behavior, and
     also shows the proper way to toggle, enable or disable the minor
     mode based on the raw prefix argument value.

          (setq transient-mark-mode
                (if (null arg) (not transient-mark-mode)
                  (> (prefix-numeric-value arg) 0)))

Any positive integer is the same as 1.
Any negative integer is the same as 0.

 t  is the same as 1.
`-' is the same as 0.

 (4) is the same as 1.
(-4) is the same as 0.
 (0) is the same as 0.

(t) is the same as 1.

(nil) and (-): behavior not conventionally defined

nil always toggles. It lets you do just `M-x foo' to toggle (the most common
change).

You can do `C-u M-x foo' or `C-9 M-x foo' to turn it on and `C-- M-x foo' to
turn it off.

etc.

bug#4102: 23.1.50; recentf-mode nil but toggles

[Xah Lee]

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Thanks Drew and all in this thread for the info.
 Xah

On Wed, Aug 12, 2009 at 9:15 PM, Drew Adams <drew.adams@oracle.com> wrote:

> > Is there somewhere in elisp manual that
> > explicitly explains/warns that commands that turn minor mode on/off
> > stick to 1 and 0 and consider t and nil not acceptable argument?
>
> (elisp) Minor Mode Conventions:
>
>   * Define a command whose name is the same as the mode variable.  Its
>     job is to enable and disable the mode by setting the variable.
>
>     The command should accept one optional argument.  If the argument
>     is `nil', it should toggle the mode (turn it on if it is off, and
>     off if it is on).  It should turn the mode on if the argument is a
>     positive integer, the symbol `t', or a list whose CAR is one of
>     those.  It should turn the mode off if the argument is a negative
>     integer or zero, the symbol `-', or a list whose CAR is a negative
>     integer or zero.  The meaning of other arguments is not specified.
>
>     Here is an example taken from the definition of
>     `transient-mark-mode'.  It shows the use of `transient-mark-mode'
>     as a variable that enables or disables the mode's behavior, and
>     also shows the proper way to toggle, enable or disable the minor
>     mode based on the raw prefix argument value.
>
>          (setq transient-mark-mode
>                (if (null arg) (not transient-mark-mode)
>                  (> (prefix-numeric-value arg) 0)))
>
> Any positive integer is the same as 1.
> Any negative integer is the same as 0.
>
>  t  is the same as 1.
> `-' is the same as 0.
>
>  (4) is the same as 1.
> (-4) is the same as 0.
>  (0) is the same as 0.
>
> (t) is the same as 1.
>
> (nil) and (-): behavior not conventionally defined
>
> nil always toggles. It lets you do just `M-x foo' to toggle (the most
> common
> change).
>
> You can do `C-u M-x foo' or `C-9 M-x foo' to turn it on and `C-- M-x foo'
> to
> turn it off.
>
> etc.
>
>


-- 
 Xah
∑ http://xahlee.org/

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