Customising Guile's prompt

Hi! I've read the HTML manual and I have created a 'nice'
prompt for my machines as follows:

(use-modules ... (system repl common))
...
(repl-default-option-set! 'prompt
  (string-append
    (getlogin) "@" (gethostname) " > "))

What bothers me is that I have been unable to replicate
the default prompt's feature of printing the current
debug (level/frame? don't even know how to call it!)

I've searched in my /usr/local/share/guile (I am on BSD)
to no avail. Could you point me in the right direction here?
BR, Ray.-