Re: mixing argument types

[Stefan Monnier]

> (defun do-a-on-b (a b &optional start stop)
>   (interactive
>     ;; check (use-region-p)
>     (list 
>       ;; ask for a
>       ;; ask for b
>       start
>       stop)
>       ;; ...
>       )

The interactive spec can't use `start` and `stop` like you did, since
it (the interactive spec) is what is used to find the arguments to pass
to the function (i.e. to find `start`, `stop, `a`, and `b`).

So you'd write:

    (defun do-a-on-b (a b &optional start stop)
      (interactive
        (list
          (completing-read "Give me A: " '("foo" "bar"))
          (read-file-name "Give me B:")
          (region-beginning)
          (region-end)))
      ...)


-- Stefan