Currently I am using libglade for building gui. However, I would like to use gtkbuilder. I couldn't find gtkbuilder interface in lablgtk2 (OCaml interface to gtk+). Is it not available in lablgtk2?
According to the comments in this bug report, it seems like gtkbuilder support will come along with the switch to Gtk3:
https://forge.ocamlcore.org/tracker/index.php?func=detail&aid=1058&group_id=220&atid=1032
The issue of migration to Gtk3 in lablgtk was discussed in July 2011:
https://lists.forge.ocamlcore.org/pipermail/lablgtk-list/2011-July/001910.html
In the former bug report comment (from April 2012), there is the insinuation that this switch might happen soon.
Sorry if the answer isn't too useful, but it is nice that the developers share these hints about what's coming up in the future.