Subclassing gtk-list-store

Hi,

I'd like to make a tree model where the data was a nodeset obtained
from an xpath query on an sxml tree.  The nicest way seems like it
should be...

(define <item-defs> (<gtk-list-store>)
   nodelist)

(define-method (initialize (obj <odm-item-defs>) initargs)
  (next-method)
  ;; set column types to attributes of each root in nodelist
  (gtk-list-store-set-column-types 2 '(gtype:gint gtype:gchararray)))

...but it seems the `gtk-list-store-set-column-types' is not exported.
 I rooted around in the source code a while and it does seem like
there's a definition for it in the defs module but I can't work out
how to use it.

Please can you point me in the right direction.

Thanks,
Andy