'(emacs)Init Syntax' customizable minor mode variables

'(emacs)Init Syntax' customizable minor mode variables

[YE]

Hello,

Could someone provide an example(s) for the "customizable minor mode
variables" that "do special things to enable the mode"?

The full sentence from the `(info "(emacs)Init Syntax")' node:

>    Some customizable minor mode variables do special things to enable
> the mode when you set them with Customize, but ordinary ‘setq’ won’t do
> that; to enable the mode in your init file, call the minor mode command.

RE: [External] : '(emacs)Init Syntax' customizable minor mode variables

[Drew Adams]

> Could someone provide an example(s) for the "customizable minor mode
> variables" that "do special things to enable the mode"?
> 
> The full sentence from the `(info "(emacs)Init Syntax")' node:
> 
> >    Some customizable minor mode variables do special things to enable
> > the mode when you set them with Customize, but ordinary ‘setq’ won’t
> > do that; to enable the mode in your init file, call the minor mode
> > command.

Good question.

This was more true before `define-minor-mode', IMO.
Before that, just `defun' was used to define a mode
command, and a `defcustom' defined its mode variable.

But the real point behind that, IMO, goes beyond minor
modes.  When a user option gets set, it's sometimes
important, or convenient, to carry out some associated
actions.

A minor-mode command is, among other things, a way
(the recommended way) to set its value, which records
whether the mode is on or off.  Since the command sets
the variable it is also the natural place to carry out
any actions associated with setting it.

If a user isn't aware that the command does more than
change the option value, just using `setq' to change
the value won't perform the associated actions.  That
might be disastrous, or it might just fail to do some
things that are desirable but not very important.
You might see that the mode was turned on/off OK when
you used setq, but you might not notice (e.g. right
away) that other things didn't happen as they should.  

For a user option more generally (not a mode variable),
there isn't necessarily a command to set the option.
And even if there is, some users might not be aware
that that's the way to set it (so that the associated
actions take place).

Simple example: When this option is set, function
`echo-bell-update' takes place, to do some other
things that take into account the changed value.

(defcustom echo-bell-background "Aquamarine"
  "Background color for `echo-bell-string'."
  :type  'color
  :set   (lambda (sym defs)
           (custom-set-default sym defs)
           (echo-bell-update))
  :group 'user)

The :set function takes care of this, as long as
you use Customize (or one of its functions, such as
`customize-set-variable) to set the value.

The `custom-set-default' part sets the option value,
and the `echo-bell-update' part carries out the
necessary actions associated with the value having
changed.

`setq' knows nothing about any actions that might
logically be associated with change a variable's
value.

In sum, if setting a variable is associated with
some actions then `setq' isn't the way to go.

Re: [External] : '(emacs)Init Syntax' customizable minor mode variables

[YE]

Thank you, Drew.

Re: '(emacs)Init Syntax' customizable minor mode variables

[Michael Heerdegen]

YE <yet@ego.team> writes:

> Could someone provide an example(s) for the "customizable minor mode
> variables" that "do special things to enable the mode"?

Enabling a mode has a lot of side effects - it's no surprise that most
modes can't be enabled by just setting the mode's variable.  Just as
adding "MODE" to the mode-line won't enable the mode.

There are some special examples where setting the mode variable does
suffice to turn the mode, but that's due to the kind of implementation
(you can, for example, set up the mode so that it is on, more or less,
all the time, but permanently watches the variable and does nothing and
stays silent when the variable is nil).

Michael.

Re: '(emacs)Init Syntax' customizable minor mode variables

[YE]

Michael Heerdegen <michael_heerdegen@web.de> writes:

> YE <yet@ego.team> writes:
>
>> Could someone provide an example(s) for the "customizable minor mode
>> variables" that "do special things to enable the mode"?
>
> Enabling a mode has a lot of side effects - it's no surprise that most
> modes can't be enabled by just setting the mode's variable.  Just as
> adding "MODE" to the mode-line won't enable the mode.

That's right. It's hard to comprehend that sentence also because one
normally doesn't expect variables to perform an action, especially "to
enable the mode". Typically, one expects functions to do the action and
variables to store values.

(I suppose it's rightful to say "normally" and "typically" here, looking
from the point of view of an average modern programmer.)

As Drew had already mentioned, part of this confusion comes from the
fact 'defcustom' can not only store values but also do things (':set').
And which frustrates not aware users from time to time (when they try to
change a user option value with an ubiquitous 'setq' but that doesn't
work).

> There are some special examples where setting the mode variable does
> suffice to turn the mode, but that's due to the kind of implementation
> (you can, for example, set up the mode so that it is on, more or less,
> all the time, but permanently watches the variable and does nothing and
> stays silent when the variable is nil).

I find this example helpful, thank you.

Does it mean the word "enable" in that paragraph should be read not as
"turn on the minor mode" but rather "store a state marker for the turned
on minor mode"? If it is so, than the source of my confusion regarding
that sentence is found.

The discussed sentence:
>    Some customizable minor mode variables do special things to enable
> the mode when you set them with Customize, but ordinary ‘setq’ won’t do
> that; to enable the mode in your init file, call the minor mode command.

Re: '(emacs)Init Syntax' customizable minor mode variables

[Michael Heerdegen]

YE <yet@ego.team> writes:

> That's right. It's hard to comprehend that sentence also because one
> normally doesn't expect variables to perform an action, especially "to
> enable the mode". Typically, one expects functions to do the action and
> variables to store values.

In that case they are more than plain Elisp variables, in some sense.

It's good that we have a different name: "(user) options".

> Does it mean the word "enable" in that paragraph should be read not as
> "turn on the minor mode" but rather "store a state marker for the turned
> on minor mode"? If it is so, than the source of my confusion regarding
> that sentence is found.
>
> The discussed sentence:
> >    Some customizable minor mode variables do special things to enable
> > the mode when you set them with Customize, but ordinary ‘setq’ won’t do
> > that; to enable the mode in your init file, call the minor mode
> command.

Note that what I mentioned was only describing one possibility (of a
minority of minor modes).  I think in the majority of cases the setter
just calls the mode function (`custom-set-minor-mode').  Doing "special
things" is probably an exception.

So what you should keep in mind that (setq MODE-VARIABLE VALUE) doesn't
turn the mode in a lot of cases, but Customize is more user friendly (as
a graphical interface), so it takes care of all cases and setting the
mode variable from Customize should always work.  In most cases setting
the mode variable from Customize will just call the mode function.

Michael.

Re: '(emacs)Init Syntax' customizable minor mode variables

[YE]

Thanks, Michael.

This discussion answered the questions I had on the topic at this stage.