How to use gnus-summary-universal-argument

[Cecil Westerhof]

I move spam message from different places to a certain folder to be
processed. I like them to be easily marked as read. I can do this with:
    M P A
    M-&
    d
but I am a real programmer and lazy: I do not want to do what I can let
the computer do. ;-]

So I started writing the following function:
    (defun gnus-summary-mark-all-messages-as-read ()
      "If in gnus-summary-mode mark all messages as read"
      (interactive)
      (if (not (equal major-mode 'gnus-summary-mode))
          (message "This function can only be used in gnus-summary-mode")
        (gnus-uu-mark-all)
        (gnus-summary-universal-argument 'gnus-summary-mark-as-read-forward)))

This does not work. The description of gnus-summary-universal-argument
is:
    gnus-summary-universal-argument is an interactive compiled Lisp
    function.

    (gnus-summary-universal-argument ARG)

    Perform any operation on all articles that are process/prefixed.

How do I need to define the argument to let this work?

On a side note: what would be a good key to bind this function to?

-- 
Cecil Westerhof
Senior Software Engineer
LinkedIn: http://www.linkedin.com/in/cecilwesterhof