[plt-scheme] Hang in macro stepper when macro expansion does not terminate

Hello,

When trying to use the macro stepper on a program whose macro  
expansion does not terminate, the macro stepper will hang, and  
clicking Stop in the editor window toolbar does not help. Sending a  
SIGINT to the DrScheme process resolves the issue. I'm not expecting  
it to not hang if a form on the right-hand side of a `define-syntax'  
or `let-syntax' recurses infinitely, but when the expansion process  
does not terminate, it would still be nice to be able to use the macro  
stepper to determine what's going on.

Just for clarity, this is an example of the type of program I'm  
talking about:

#lang r5rs

(define-syntax foo
   (syntax-rules ()
     ((_) (foo))))

(foo)
--
Brian Mastenbrook
brian at mastenbrook.net
http://brian.mastenbrook.net/