The main feature that the interpreter lacks that I wish for is arbitrary precision arithmetic.  Adding arbitrary precision arithmetic to the interpreter is not impossible but it would not be a trivial undertaking at all.  Much of the code would need to be re-written.

I'm  going to continue to study the code to assess the amount of work that will be involved.

Also I worked for nearly 1 week trying to create a GUI version of the program, but now I'm not sure if this is even possible.  The way the code is written all results are simply dumped to the terminal one character at a time from within an evaluation loop. 

If anyone has any interest in helping out please contact me.  The source code is in the form of Visual Studio 2010 Express C++ .