[racket] generator performance

Four things that might be helpful, in this case, and in general for 
optimizing Racket code:

1. Use statistical profiler to see who is actually eating the time: 
http://doc.racket-lang.org/profile/index.html  Increasing the sampling 
resolution can help.

2. Use DrRacket "Macro Stepper" to see exactly how the code expands.  I 
often just hit the "End" button, rather than stepping through.  
Adjusting "Macro hiding" thing at the bottom of the window can also help.

3. Look at implementation of "generator" in the Racket source code.

4. Sam's disassembler: 
http://lists.racket-lang.org/dev/archive/2011-January/005321.html

Neil V.