;;; this would go into slime.el
(defun slime-eval-custom-expand (expander exp-str package buffer-name buffer-mode printer)
  (lexical-let ((package package)
                (buffer-name buffer-name)
                (buffer-mode buffer-mode)
                (printer printer))
    (slime-eval-async
     (list 'swank:eval-and-grab-output (format "(%s %s)" expander exp-str))
     (lambda (expansion)
       (with-current-buffer (slime-get-temp-buffer-create buffer-name :mode buffer-mode :reusep t)
         (setq slime-buffer-connection (slime-connection))
         (setq slime-buffer-package package)
         (setq buffer-read-only nil)
         (erase-buffer)
         (insert (funcall printer (second expansion)))
         (setq buffer-read-only t)
         (font-lock-fontify-buffer)))
     package)))

(defun* slime-add-custom-expander (key expander buffer-name &optional (buffer-mode 'slime-mode) (printer #'identity))
  (slime-define-key key (lexical-let ((expander expander)
                                      (buffer-name buffer-name)
                                      (buffer-mode buffer-mode)
                                      (printer printer))
                          (lambda (&rest _)
                            (interactive "P")
                            (slime-eval-custom-expand expander
                                                      (first (slime-sexp-at-point-for-macroexpansion))
                                                      (slime-current-package)
                                                      buffer-name
                                                      buffer-mode
                                                      printer)))
                    :prefixed t :inferior t))

;;; This stuff would go into .emacs
(slime-add-custom-expander "j" 'ps:ps "*ParenScript generated Javascript*" 'js-mode #'read)

(provide 'js-expander)