Re: Using the :set to make an alist

On Wednesday, August 19th, 2026 at 11:52 AM, 
[email protected] <[email protected]> wrote:

> Heime <[email protected]> writes:
> 
> > I want a customisable variable that is an alist with elements (key . directory-path).
> >
> > Have made the :set function to set the list by appending sub-directories using orellana-fpln base directories. Because usually one uses (set-default symbol value) to set the value, I do not understand how this can be applied to a list.
> >
> >  (defcustom galaxiakos-fpln nil
> >   "Association List (alist) specifying a flight plan, where each element is
> > a cons cell (WAYPT . DIRECTORY-PATH) linking a waypoint code to its
> > associated directory path for different Galaxiakos components."
> >   :group 'galaxiakos
> >   :type  '(alist :key-type (symbol :tag "Code")
> >                  :value-type (string :tag "Path"))
> >   :set  (lambda (symbol value)
> >           (set-default symbol value)
> >           (let ( (glxks-waypt  (assoc-default 'GLXKS orellana-fpln) )
> >             (when glxks-waypt
> >               (setq galaxiakos-fpln
> >                      `((GLXKS . ,glxks-waypt)
> >                        (OMNIX . ,(concat glxks-waypt "/omniskon"))
> >                        (PROTL . ,(concat glxks-waypt "/protilus"))
> >                        (GRGRS . ,(concat glxks-waypt "/gregers"))) )) )) )
> >
> >
> 
> 1. Using ‘setopt’, the value of ‘galaxiakos-fpln’ can be set to
> the alist '((PROTL . "path1") (OMNIX . "path2")) as follows:
> 
>   (setopt galaxiakos-fpln '((PROTL . "path1") (OMNIX . "path2")))
> 
>   C-h v galaxiakos-fpln RET
> 
>   galaxiakos-fpln’s value is ((PROTL . "path1") (OMNIX . "path2"))
> 
> 2. If ‘orellana-fpln’ is set to an association list with an
> entry for ‘GLXKS’, then the value of ‘galaxiakos-fpln’ will
> be set according the value that corresponds to the ‘GLXKS’ entry.
> 
> So, if the entry is, say, (GLXKS . "my-path"), then
> 
>    (setopt galaxiakos-fpln '((PROTL . "path1") (OMNIX . "path2")))

Where should I call setopt exactly?
 
> will *NOT* add these values to ‘galaxiakos-fpln’.  Instead,
> its value will be:
> 
>    ((GLXKS . "my-path")
>     (OMNIX . "my-path/omniskon")
>     (PROTL . "my-path/protilus")
>     (GRGRS . "my-path/gregers"))
> 
> 3. Your question does not describe what you want the :set
> function to do.  If you want it to add/change/delete a set
> of key/value pairs, then you will need to change your
> function to update the association list.  See:

I want users to change the paths should they prefer.
 
>    M-x shortdoc alist
> 
> and
> 
>    (info "(elisp) Association Lists")
> 
> 4. You might want to write the :set function as a separate
> function outside of the (defcustom ...) form to define what
> you want it to do, and then add the function definition to
> (defcustom ...)  after you have worked out the details.
 
Have made the separate function

(defun galaxiakos-fpln-update (symbol value)
  "Custom setter for `galaxiakos-fpln'.
Updates the variable's value and refreshes internal path associations."
  (set-default symbol value)
  (let ((glxks-waypt (assoc-default 'GLXKS orellana-fpln)))
    (when glxks-waypt
      (set symbol
            `((GLXKS . ,glxks-waypt)
              (OMNIX . ,(concat glxks-waypt "/omniskon"))
              (PROTL . ,(concat glxks-waypt "/protilus"))
              (GRGRS . ,(concat glxks-waypt "/gregers")))))))

(defcustom galaxiakos-fpln nil
  "Association List (alist) specifying a flight plan, where each element is
a cons cell (WAYPT . DIRECTORY-PATH) linking a waypoint code to its
associated directory path for different Galaxiakos components."
  :group 'galaxiakos
  :type  '(alist :key-type (symbol :tag "Code")
                 :value-type (string :tag "Path"))
  :set #'galaxiakos-fpln-update)

> The lyf so short, the craft so long to lerne.
> - Geoffrey Chaucer, The Parliament of Birds.
> 
>