[plt-scheme] graphs / shared

Hi,
In another thread, graphs were suggested as replacement for streams.

I tried to play with them (a little) and didn't get very far. They
seem very nice for the simple things (well, for graphs), but there are
some things that I can do with streams that I don't see how I can
achieve with them (or maybe I didn't understand the answers I got
then, and it is really not possible).

I would like to learn how graphs can be used to construct a finite but
long repeated sequence, in a manner which is as efficiant as streams
in terms of memory usage..

Thanks!

Yoav