defcustom - restricted list of symbols

defcustom - restricted list of symbols

[Joe Casadonte]

I'd like to write a defcustom variable definition that:

1. is a symbol (but could be a string, if need be)
2. is one of a list of "acceptable" symbols
3. the complete list of "acceptable" symbols is not know at the time I
   write I write the defcustom itself (but is known at run-time)
4. by the nature of #3, I need to be able to add to the list of valid
   symbols
5. presented to the user as a radio button or check box would be

Here's an example:

Let's say I have a generic dictionary front-end module, and I ship
with the two dictionaries: English and German.  When the user goes to
customize the 'default-dictionary' for this module, I want them to be
able to choose between English, German and any other dictionary they
have installed.  I don't know at the time I write the front-end which
dictionaries are available (as more could be added), and I don't know
which the user will have installed.  I can, however, count on the
proper installation of a dictionary to update some other variable,
which comprises a list of installed dictionaries.

If that is somehow possible, is it then possible to make this variable
just one element in a list of values that comprise a single variable?
To continue the above (completely contrived) example, say I want to
link a given mode and a default dictionary, so that message-mode uses
German as the default, and text-mode uses English.  Normally I would
create a compound defcustom definition, using the 'list type and
choice and what-not.

Now, assuming all of that *is* possible, is there a reason not to use
it?  Care would have to be taken to ensure that the list of installed
dictionaries is known *before* `custom-set-variables' is called.  But
I think that's possible to do given the :set-after and :require
keywords.

Thanks for the help!

--
Regards,


joe
Joe Casadonte
jcasadonte@northbound-train.com

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Re: defcustom - restricted list of symbols

[Magnus Henoch]

"Joe Casadonte" <jcasadonte@northbound-train.com> writes:

> I'd like to write a defcustom variable definition that:
>
> 1. is a symbol (but could be a string, if need be)
> 2. is one of a list of "acceptable" symbols
> 3. the complete list of "acceptable" symbols is not know at the time I
>    write I write the defcustom itself (but is known at run-time)
> 4. by the nature of #3, I need to be able to add to the list of valid
>    symbols
> 5. presented to the user as a radio button or check box would be

This seems to work:

(eval-when-compile (require 'cl))

(defcustom malekzista 'foo
  "An option with restrictions decided at runtime."
  :type '(radio (const foo)))

(defun malekzista-add-option (new-option)
  "Add new option to variable `malekzista'."
  (push (list 'const new-option) (cdr (get 'malekzista 'custom-type))))

Magnus

Re: defcustom - restricted list of symbols

[Joe Casadonte]

On Mon, 16 Oct 2006, Magnus Henoch wrote:

> This seems to work:

Thanks, Magnus -- that's awesome!  By trying to use it, though, I
found my "design" is unwieldy, as it will require me to modify many,
many variables.  Your example, though, led me to this:

   (defvar joe-available-dictionaries
     '(choice :tag "Dictionaries"
              (const :tag "English (US)" english-us)
			  (const :tag "German" german)))

   (defcustom joe-foo nil
	 ""
	 :type `(repeat
			 (list
			  (string :tag "Foo")
			  ,joe-available-dictionaries
			  (string :tag "Bar")))
	 :group 'joe)

which is much closer to what I want (though not at all what I asked
for originally).  Now, I only have one variable to manipulate.

Thanks!

--
Regards,


joe
Joe Casadonte
jcasadonte@northbound-train.com

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