Re: A way for interactive to modify a let-bound variable?

[Kaushal Modi]

This is the actual function I want to optimize (Reference:
http://thread.gmane.org/gmane.emacs.help/109025/focus=109137 ).

(defun modi/advice-region-or-whole (orig-fun &rest args)
  (interactive (if (use-region-p)
                   (list (region-beginning) (region-end))
                 (list (point-min) (point-max))))
  (prog1
      (apply orig-fun args) ; this defun NEEDS to return this form's value
    (when (and (called-interactively-p 'interactive) ; duplication of
condition
               (not (use-region-p)))                           ;
      (message "Executed %s on the whole buffer."
               (propertize (symbol-name this-command)
                           'face 'font-lock-function-name-face)))))

This is an :around advice function and it needs to return the (apply
orig-fun args) value.

> You can of course use `let' _inside_ `interactive'

If I move the let form inside interactive, the let form needs to return the
list required for interactive. Then how would I return the (apply ..) value?

Eventually I want something like below that actually works:

(defun modi/advice-region-or-whole (orig-fun &rest args)
  (let (msg)
    (interactive (if (use-region-p)
                     (list (region-beginning) (region-end))
                   (setq msg (format "Executed %s on the whole buffer."
                                     (propertize (symbol-name this-command)
                                                 'face
'font-lock-function-name-face)))
                   (list (point-min) (point-max))))
    (prog1
        (apply orig-fun args)
      (when msg
        (message msg)))))