Why no setq, eval in a dir-locals?

Why no setq, eval in a dir-locals?

[Colin Baxter 😺]

Hello,

To backup tex files in the same working directory, I have a .dir-locals
file containing the following lines:

#+begin_src emacs-lisp
((latex-mode . (
(kept-old-versions . 2)
(kept-new-versions . 16)
(delete-old-versions . t)
(make-backup-files . t)
(version-control . t)
)))
#+end_src
It works well.

I am curious though as to why I do not seem to need "setq" and "eval"
terms. These are needed however if I wish to put the backups in a
sub-directory:

#+begin_src emacs-lisp
((latex-mode . (
(eval setq backup-directory-alist '(("." . "sub-directory/")))
(kept-old-versions . 2)
(kept-new-versions . 16)
,,, etc.
#+end_src

This too works well.

Can anyone tell me why the two cases appear to be different.

Thank you.

Best wishes,

Re: Why no setq, eval in a dir-locals?

[irek]

Colin Baxter 😺 <m43cap@yandex.com> writes:
> I am curious though as to why I do not seem to need "setq" and "eval"
> terms. These are needed however if I wish to put the backups in a
> sub-directory:
>
> #+begin_src emacs-lisp
> ((latex-mode . (
> (eval setq backup-directory-alist '(("." . "sub-directory/")))
> (kept-old-versions . 2)
> (kept-new-versions . 16)
> ,,, etc.
> #+end_src
>
> This too works well.
>
> Can anyone tell me why the two cases appear to be different.

.dir-locals is not elisp file that gets evaluated like init.el file that
holds your Emacs configuration.  .dir-locals hold (variable like) value.
It describes in what context (latex-mode in this example), what variable
(for example kept-old-versions) what value should be assigned (in case
of kept-old-versions in latex-mode in your example it's 2).

You can't put regular elisp code inside .dir-locals like `defun',
`setq', `global-set-key' etc.  But if you need then you can use `eval'
keyword.  Code after `eval' is evaluated so you can put any valid elisp
expression after it `eval'.

Not sure why do you assume that `eval setq' is required for
`backup-directory-alist' variable.  It should work the same way as you
did for other variables.  Provide variable name, period and value.

((latex-mode . (
(backup-directory-alist  . (("." . "sub-directory/")))
(kept-old-versions . 2)
(kept-new-versions . 16))))

You can read info page (info "(emacs) Directory Variables") for better
understanding.

Re: Why no setq, eval in a dir-locals?

[Colin Baxter]

Thank you for your reply.

>>>>> irek  <mail@gumen.pl> writes:

    > Not sure why do you assume that `eval setq' is required for
    > `backup-directory-alist' variable.  It should work the same way as
    > you did for other variables.  Provide variable name, period and
    > value.

    > (backup-directory-alist . (("." . "sub-directory/")))

I did originally have that line ... or at least I thought I did! That
line appeared not to work which is why I was puzzled and went on to use
eval setq. I can only assume that I originally inserted a typo
somewhere.

All is now working satisfactorily.

Thank you for your help. Next time I'll double check for typos.

Best wishes,

Colin Baxter.