Closure does not capture variable

Question

I wrote the following code, but it does not work:

(progn
  (define-prefix-command 'unicode-shortcut-keymap)
  (dolist (mapping '(("- >" . "→")))
    (let ((keys (car mapping))
          (text (cdr mapping)))
      (message text)
      (define-key unicode-shortcut-keymap (kbd keys)
        (lambda () (interactive) (insert text)))))
  (global-set-key (kbd "C-c u") 'unicode-shortcut-keymap))

When I try to use it, I get the error:

Symbol’s value as variable is void: text

But text is not void, message displays the text.

How to fix this?

Answer 1

You don't have a closure unless your file has set lexical-binding: t as a file-local variable.

Without that, everything is using dynamic binding (in which case in your example your variable is indeed bound while your function is defined but is not still bound later on, when that function is called).

See also C-hig (elisp)Converting to Lexical Binding

Answer 2

This seems to work:

(defmacro lexical (exp &rest exps)
  "Evaluate expressions with lexical scope."
  (declare (indent defun))
  `(eval '((lambda () ,exp ,@exps)) t))

(lexical
  (define-prefix-command 'unicode-shortcut-keymap)
  (dolist (mapping '(("- >" . "→")))
    (let ((keys (kbd (car mapping)))
      (insert-text (lambda () (interactive) (insert (cdr mapping)))))
      (define-key unicode-shortcut-keymap keys insert-text)))
  (global-set-key (kbd "C-c u") 'unicode-shortcut-keymap))