Signaling text-read-only

[Deniz Dogan <deniz.a.m.dogan@gmail.com>]

I have a situation here where I need to tell the user that the part of
the buffer where point is located is read-only. This is what I am
thinking right now:

(unless (rcirc-looking-at-input)
  (error (error-message-string (list 'text-read-only)))

or:

(unless (rcirc-looking-at-input)
  (signal 'text-read-only nil)))

I haven't found any examples of this explicit sort of signaling in the
other Lisp files in Emacs, but I might have missed something.

The reason why I need this is that `rcirc-complete' shouldn't be
called in read-only areas of the buffer.

What is the right way to do this?

-- 
Deniz Dogan