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Re: About the `:variable' keyword in `define-minor-mode'
From: |
Michael Heerdegen |
Subject: |
Re: About the `:variable' keyword in `define-minor-mode' |
Date: |
Thu, 14 Feb 2013 16:53:13 +0100 |
User-agent: |
Gnus/5.13 (Gnus v5.13) Emacs/24.3.50 (gnu/linux) |
Stefan Monnier <monnier@iro.umontreal.ca> writes:
> > In the docstring of `define-minor-mode':
> > [...]
> > :variable PLACE [...]
> > PLACE can also be of the form (GET . SET), where GET is
> > an expression that returns the current state, and SET
> > is a function that takes one argument, the new state,
> > and sets it.
>
> > I don't understand the meaning of GET. The docstring says it returns
> > the current state, but where will it return?
>
> It will return it to the context?
I think he wanted to know where and how it is referenced/used (in the code).
Xue, please have a look at the definition of the macro
`define-minor-mode'. The GET part is used in the defun of the modefun,
after these lines:
;; The actual function.
(defun ,modefun (&optional arg ,@extra-args)
There, the variable `mode' is bound to the GET expression. It is mainly
used to check if the mode is on or off, but it is also `setf'ed if SET
is nil.
So, if e.g. GET is `(car foo)', the car of the value of the variable
`foo' will be looked at to decide whether the mode is turned on or off.
Does this help?
Regards,
Michael.