`make-variable-frame-local'

[Oliver Scholz]

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In GNU Emacs 21.2.1 (i686-pc-linux-gnu, X toolkit, Xaw3d scroll bars)
 of 2002-04-29 on hermes
configured using `configure  --with-gif --with-png --with-x-toolkit=lucid 
--with-xpm --with-jpeg --with-tiff'
Important settings:
  value of $LC_ALL: nil
  value of $LC_COLLATE: nil
  value of $LC_CTYPE: nil
  value of $LC_MESSAGES: C
  value of $LC_MONETARY: nil
  value of $LC_NUMERIC: nil
  value of $LC_TIME: nil
  value of $LANG: de_DE
  locale-coding-system: iso-latin-1
  default-enable-multibyte-characters: t

Please describe exactly what actions triggered the bug
and the precise symptoms of the bug:

Is it possible that there is a bug in `make-variable-frame-local' or
am I missing something here?

I do the following in a fresh Emacs (v 21.2) started with -q and
-no-site-file:

I eval this in *scratch*:

(defvar sframes-mode nil)
(make-variable-frame-local 'sframes-mode)

(setq sframes-mode 'lirum-larum)

Then I make a new frame with `C-x 5 2'. I eval this in the new frame:

(setq sframes-mode 'schubi-dubi)

Then I go back to frame #1 and do `C-h v sframe-mode RET':

==> sframes-mode's value is schubi-dubi

In other words: `sframes-mode' still behaves so far like a global
variable. :-(

---

Now the docs mention frame-parameters in the context of
`make-variable-frame-local'.

Again in a fresh Emacs with -q --no-site-file:

frame #1:

    (defvar sframes-mode nil)

    (make-variable-frame-local 'sframes-mode)

    (modify-frame-parameters nil '((sframes-mode . lirum-larum)))

    sframes-mode
      => lirum-larum

Then I create frame #2:

    sframes-mode
      => nil

    (setq lirum-larum 'schubi-dubi)

Back to frame #1:
    sframes-mode
      => lirum-larum

So after I touched the frame-parameters once, everything works as
expected.

---

Now, how do I work around this? Do I have to do modify the
frame-parameters once for every frame-local variable? Or is there a
better way? I need it to implement a frame-local minor-mode.

    -- Oliver