[plt-scheme] Slime-like documentation

Hi

I wanted to begin hacking DrScheme/MzScheme and wanted to know if it's  
possible to know the name and parameters of every defined function  
(and special form/macro) in the environment so I could make Dr. Scheme  
do something like slime in emacs:

When you write "(nth ", emacs shows "(nth N LIST)" in the mini-buffer.

Is it possible to get that information? Where should I start looking  
in the Dr Scheme code-base to add that to the interface?

Thanks for the information,

   - Filipe Cabecinhas