I've learned painfully that application development requires intensive GUI work. But I also believe that part of the beauty of APL is the ability to work very efficiently without a GUI and we hope that part of the beauty we enjoy is the ability to port easily to a new application environment or to use objects in a new way (or a new application).
For these reasons, it is terribly important to focus on APL tools that help us separate basic functionality from the particular GUI appropriate for an application.
The following structure is suggested (suggestions & comments are very welcome). An application using the WRP Google paper published in Vector might be used as an example. (it is possible that all good programmers already work this way and I am just way behind the curve)