Question

In my Emacs config I have such a string:

(setq ibuffer-saved-filter-groups
  (quote (("default"
           ("dired"
            (mode . dired-mode))
           ("System"
            (or (name . "\*scratch\*")
                (name . "\*Messages\*")))
           ("SVN"
            (name . "^\\*vc-.*\\*$"))))))

The variables name and mode are undefined but the code is evaluated correctly. When I try to make a such on my own:

(some-var . "some-value")

I receive an error about the undefined variable some-var.

Answer 1

When a datum is quoted, nothing within is evaluated. For example:

foo

evaluates to the value bound to the identifier foo, whereas

'foo

or

(quote foo)

evaluates to the symbol foo.

Likewise,

(+ 1 2 3)

evaluates to 6, whereas

'(+ 1 2 3)

or

(quote (+ 1 2 3))

evaluate to a list with four elements: the symbol +, and the numbers 1, 2, and 3. In particular, the + is not evaluated.

Similarly, your name and mode, both being within the quoted datum, are not treated as identifiers, but as symbols. They are not evaluated.