portable GUI , Ada backend, best design?

[nma123@super.zippo.com]

Hello,

I am seeking advice on this.

I'd like to do this:

      +-----------+     +--------------------+
      | GUI       |     | analysis           |
      | for data  |<===>| and                |
      | entry     |     | computational part |
      +-----------+     +--------------------+

Where the software must be portable with no code changes when building the
software on UNIX and Windows.

I looking at using  Ada (GNAT) for the analysis and computational part 
of the system, using Ada insures portability for the backend side.
 
The problem is what to use for the GUI part. the GUI part is for entering
user input, the parameters for the analysis part, so it is not very advanced
GUI, but it had to be portable.

I can look at using tcl/tk for the GUI, since tcl/tk is avaliable on both
UNIX and windows. has anyone used tcl/tk and called Ada from it? any problems?
can Ada make a callback into tcl/tk function to be able to update 
the GUI screen? I have not used tcl/tk, although played with some 
tcl/tk GUI scripts.

I can may be use Java for the GUI and use JNI to interface to C code that
calls Ada, the Ada calling C back that calls Java to update the GUI.

offcourse I can use X and Ada but that is not portable.

Any other ideas? how to do portable GUI that interfaces to Ada?

thanks,
n.