could anyone point me to any documentation (code, book, article, ...) that would teach me how to go about writing a step debugger for arc? mostly doing it for my own amusement, but i don't know where to start. thanks.
Before getting into modifying the Arc compiler you may want to try an easier step first: write an Arc interpreter in Arc, which you can then easily make step through the program to be debugged.
ac.scm is the scheme code that compiles arc into scheme. This would be an appropriate place to plug in a debugger, by adding hooks in, for example, ar-funcall0 and ar-apply. Otherwise, there are debuggers for scheme, but using one of those wouldn't be as much fun as writing one ...
you might find inspiration in the debuggers that come with rainbow or jarc.