defcustom - restricted list of symbols

["Joe Casadonte" <jcasadonte@northbound-train.com>]

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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