Emacs: string interpolation with property lists

interpolate-plist.el

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

(defun interpolate-wrap-key (str sym)
  (get sym (intern (concat ":" str))))

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

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