[plt-scheme] maintaining a cached list of modules

Hi,

I've just written a bit of Scheme code that traverses the collection
directories and creates a list of available modules (so that i can get
module path completion in emacs). Since it's a big list, i cache it; but
now imagine that i require, say, a new PLaneT package in the same
mzscheme session: my cache becomes stale. Is there any way of
'intercepting' calls to REQUIRE, or some other technique allowing me to
keep the module list fresh?

Thanks!
jao
-- 
Lisp has assisted a number of our most gifted fellow humans in
thinking previously impossible thoughts. —Edsger Dijkstra