For kicks I would like to write a minimalistic GUI interface to the 
debugger.

I prefer C++ or C# for GUI applications (this is not to debate here).

What is the best way to establish communication between my GUI and the 
default ruby debugger?

As a starting point, I would just like the gui to show the file being 
debugged and the current line of execution.  The debug commands will be 
set in a command window.

A point in the right direction would be helpful.

~S