[plt-scheme] trying to understand PLAI route-producer code...

 > I'm quite desperately trying to understand the route-producer code
 > from PLAI (the mutating version) for some time now,  but somehow I
 > don't get it ...

> Perhaps someone has time for a littel hint what to do to understand  
> the code...

Do a full trace by hand using the lambda^ notation to represent 
continuations. In fact, do this for the buggy code that precedes it, and 
make sure you thoroughly understand what goes wrong there first.

The reason my name is in the PLAI acknowledgements is because I did this 
and sent some comments to Shriram. Along the way, trying also to tweak 
the code and execute it to see what happened, I discovered a small bug 
in the way the then-current version of DrScheme handled the interaction 
between continuations and the REPL. (Cue Matthew: "the top level is 
hopeless".) --PR