[plt-scheme] Speed up check-syntax

Matthias asked:

>>> Could we approximate parallelism with a 'niced' threading model?

and Robby replied:

> I think what you're asking is if the parallelism we get from the disk
> and the cpu is already enough to get some speed up here(?). I'm not
> sure.

Forget about disk vs CPU; can't this be done in the eons between  
keystrokes?  Particularly since nobody is likely to hit "Check  
Syntax" as the first action after starting DrScheme.  There should be  
plenty of time while the user reads the screen, re-orients to the  
problem at hand, finds a spot in the source code, and makes an edit  
or two.

Stephen Bloch
sbloch at adelphi.edu