Set an empty string for function argument with list

Question

I have a function argument and want to set an empty string for name and mode. What can I do?

(defun bench (&optional name mode prefix)
  "DOCSTRING"

  (interactive
   (cond

    ((equal current-prefix-arg nil)
     (list

      current-prefix-arg)))))

Answer 1

I don’t really know what you want, but based on your comment you want the name and mode variables to be strings if the caller passes in nil or omits them. While cl-defun is an option, I wouldn’t do anything fancy at all.

Instead, when you go to use name or mode in the body of your function, just write (or name "") and (or mode "") instead. The or function looks at each argument in turn and gives you the first one that is non–nil. Like this:

(defun bench (&optional name mode prefix)
  "DOCSTRING"
  (message "name=%s mode=%s" (or name "") (or mode ""))

If you find yourself in a situation where you need to type these expressions out more than once, just use let to rebind them:

(defun bench (&optional name mode prefix)
  "DOCSTRING"
  (let ((name (or name ""))
        (mode (or mode "")))
    …))

I wouldn’t try to do anything tricky with the interactive declaration. Keep it as simple as possible.