Elisp: How do you combine interactive "r" with interactive "p"?

Question

I have an existing command (increment-numbers-in-region) which is declared using interactive "r" to get region start and end points as arguments. I would now like to extend this command to take a prefix argument as well. Is there a way to combine interactive "r" with interactive "p" or should I go about it in some other way?

I guess I could write a command which uses interactive "p" only, and then read point and mark from the command body, but it feels like that might not be the most idiomatic way.

Any ideas?

Answer 1

C-hf interactive RET

"To get several arguments, concatenate the individual strings, separating them by newline characters."

(defun increment-numbers-in-region (start end arg)
  (interactive "r\np")
  ...)