Hello Chris,
I've been following the discussions about the GTK wrapper, and while I'm not using it myself (since I work on the Emacs integration) I realise that there are plenty of (potential) overlaps between our projects.
In particular, I want to let you know about the Emacs mode backchannel protocol that the mode uses for directly communicating with the GNU APL interpreter. When started, if gives you a simple text-based protocol through which you can do things such as defining functions or creating listeners that send you a message whenever a variable is changed (this is used by the realtime variable watcher).
It would be neat if you were to consider implementing some of the feature I added to the Emacs mode, and if you do it would be useful if you used the same protocol as I am using.
Please let me know if you have any questions.
Regards,
Elias