Emacs: string interpolation of bound variables

interpolate-bound.el

(defvar interpolate-capture "%{\\([^}]+\\)}")

(defun interpolate- (str pl)
  (if (string-match interpolate-capture str 0)
      (let* ((key (match-string 1 str))
	     (new-str (replace-match "%" t nil str))
	     (new-key (eval (intern key))))
	(interpolate- new-str (cons new-key pl)))
    (cons str (reverse pl))))

(defun interpolate (str)
  (let* ((result (interpolate- str ())))
    (apply 'format result)))