[plt-scheme] debugging [mini rant]

> Indeed, a command line debugger would make easy to connect the
> debugger from other environments (SLIME?), but it's understand that it
> could be a lot of work if such debugger is currently embedded into the
> graphical environment.

Support for setting breakpoints and inspecting the stack is
implemented by source annotation and continuation marks.  All of this
is independent of any graphical interface, and an interested
programmer with some free time could build a text-based interface atop
the same underlying mechanism.

Greg