When you get an error in MIT scheme it doesn't tell you where the error occurred. For example, it just prints something like this:
;Unbound variable: top-left
;To continue, call RESTART with an option number:
; (RESTART 3) => Specify a value to use instead of top-left.
; (RESTART 2) => Define top-left to a given value.
; (RESTART 1) => Return to read-eval-print level 1.
How do I find where this error occurred in my code?