checking for nil argument in interactive

[Seb]

Hi,

I don't understand why the following arg symbol doesn't get set to
"string":


(defun funny-function (arg)
  (interactive "sarg: ")
  (if (not arg) (setq arg "string"))
  (message "arg: %s" arg))

To test:

M-x funny-function RET RET

I've also tried (eq "" arg) for the if boolean but get the same result.
Any advice would be appreciated.


Cheers,

-- 
Seb