Question

Not clear on some fundamental syntax here. define-key accepts a set of inputs, one of which is inside square braces. What is that construct? How can I dynamically generate what goes inside the square braces?

In the simple case, I can display a one-item menu like this:

(flet ((ok (&optional p1 &rest args) t))
  (setq menu-1 (make-sparse-keymap "Title"))
  (define-key menu-1 [menu-1-ok-event]
    `(menu-item "OK"
                ok 
                :keys ""
                :visible t
                :enable t))
  (x-popup-menu t menu-1))

I can insert additional menu items like this:

(flet ((ok (&optional p1 &rest args) t))
  (setq menu-1 (make-sparse-keymap "Title"))
  (define-key menu-1 [menu-1-event-ok]
    `(menu-item "OK"
                ok 
                :keys ""
                :visible t
                :enable t))
  (define-key menu-1 [menu-1-event-1]
    `(menu-item "This is line 1"
                nil
                :keys ""
                :visible t
                :enable t))
  (x-popup-menu t menu-1))

But what if I want to dynamically generate the thing inside square braces? What if I want something like this:

  (while (< n 5)
   (define-key menu-1 [(dynamic-thing n)]
    `(menu-item (format "This is line %d" n)
                nil
                :keys ""
                :visible t
                :enable t)))

I tried

   (define-key menu-1 [(intern (format "menu-1-event-%d" n))]
      ...

..but that did not work. The result is always “intern”. ???

What are the square braces? The syntax is unfamiliar to me.

Answer 1

These are vectors. [foo bar] is syntactic sugar for (quote (vector foo bar)); it’s a literal. To construct a vector where the elements need to be evaluated, use the vector built-in function explicitly; it works like list.

(define-key menu-1 (vector (format "menu-1-event-%d" n)) …

The chapter on menu keymaps may help as well.