Jean-Claude Dulac worked on this problem while he was at SEP, and wrote an interactive user interface manager called SepView (Dulac, 1988). IPE is more limited in scope than SepView, but I think its simplicity is its strength. It is easier to use or get inside of than SepView. No programming is required to use IPE or add new programs to its repertoire. Still, SepView has many nice features that IPE lacks. After I've explained IPE and how it works, I'll contrast it with SepView more carefully, and see what features of SepView can and should be incorporated into IPE in the future.
I've said that IPE is interactive, but I should qualify that statement a little. In a ``truly'' interactive program, if I change a parameter (for instance, if I modify the value in a text field or move a slider), the display is instantly updated where necessary to reflect the change. IPE is a bit more awkward. After modifying the slider or text field, I have to go and press the DOIT button Then my entire plot, not just the necessary pieces, is erased and redrawn. For this reason I would say that IPE isn't ``truly'' interactive. But it comes very close, for many different programs, at essentially no cost.
I wrote a first version of IPE a couple months ago, using Sunview, an interactive package for Sun workstations that has been around for several years. Early this year, along with a new release of X Windows from MIT came the XView toolkit, written by Sun and in many ways similar to Sunview. I converted IPE to XView, and now we have the advantage of being able to run it on all our machines - Convex, Sun, and DEC - rather than just one. Programmers familiar with Sunview will find the transition to XView relatively painless. Sun provides utilities that will do much (but not all) of the work to convert source code from Sunview to XView.