Obviously you have source code. To do what you want:

Remove your set command from the code so that it is original.

Run a bat program in the SBT root directory called makeproc.bat. This will concatenate and compile a few million (exageration) general routines that ship with SBT.

Start Visual FoxPro 5.0, and launch the debugger.

Open the program sbt.prg inside the debugger, and run it. SBT will start (a little slow), and go right on through the debugger. (Set up the an environment variable in you autoexec.bat SBTDUTIL=ON. This will let you Shift F9 to suspend the running SBT and poke around the debugger.)

Set up breakpoints and watches at will in the debugger.

Also, if you click on the developer's workbench icon in SBT, it will suspend, and they have their own dump of global variables, etc.