Make a defcustom dependent on another variable

Make a defcustom dependent on another variable

[Joost Kremers]

Hi all,

Defining a custom variable that can have one of (e.g.,) two values is
easy:

(defcustom some-option 'value1
  "Doc string"
  :group 'some-group
  :type '(choice (const value1)
                 (const value2)))

However, what if the possible values `some-option' can take are defined
in another variable? Is it ok to do something like the following:

(defcustom some-option 'value1
  "Doc string"
  :group 'some-group
  :type '(choice ,@(mapcar #'(lambda (x) `(const ,x))
                           some-option-list)))

where `some-option-list' is a variable holding a list of possible values
for `some-option'.

The code seems to work (the resulting customisation option works), but I
was wondering a) if there are any hidden problems I'm not aware of; and
b) if there is a more canonical way of doing this.

TIA

Joost



-- 
Joost Kremers                                   joostkremers@fastmail.fm
Selbst in die Unterwelt dringt durch Spalten Licht
EN:SiS(9)

Re: Make a defcustom dependent on another variable

[Thien-Thi Nguyen]

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() Joost Kremers <joost.m.kremers@gmail.com>
() 19 Mar 2014 23:05:21 GMT

   The code seems to work (the resulting customisation option works),
   but I was wondering a) if there are any hidden problems I'm not
   aware of; and b) if there is a more canonical way of doing this.

If you have the GNU Emacs source, you can grep for "choice.*mapcar"
and see how others do it.  I see 9 hits.  I choose one that is from a
fundamental library -- minibuffer.el var ‘completion--styles-type’ --
and find it in the lisp/ChangeLog.16 entry dated 2011-10-03 authored
by Stefan Monnier.  I feel comfortable using this technique now.

If you do not have the GNU Emacs source, then you can question your
sanity / situation / style / subjugation, until you do...  :-D

-- 
Thien-Thi Nguyen
   GPG key: 4C807502
   (if you're human and you know it)
      read my lisp: (responsep (questions 'technical)
                               (not (via 'mailing-list)))
                     => nil

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Re: Make a defcustom dependent on another variable

[Stefan]

> fundamental library -- minibuffer.el var ‘completion--styles-type’ --
> and find it in the lisp/ChangeLog.16 entry dated 2011-10-03 authored
> by Stefan Monnier.  I feel comfortable using this technique now.

FWIW, I'm not happy with this technique (I'd like the list of choices
to be recomputed dynamically), but it's the best I could come up with.
If someone more knowledgeable with Custom can show me how to make it
dynamic (while still making it a popup menu rather than a text field with
completion), I'd appreciate it.


        Stefan