[plt-scheme] Saving to disk.

Hi,

Is there a function available in plt-scheme to write a datastructure or 
a list to disk
and then read it back at a later date?

Or do I have to write the data to the disk in some format and then read 
it back
using a custom route to rebuild the data (could use XML I guess).

Basicly I have a program that builds a tree of lists from users input, 
and I would like
to be able to save this tree to disk, and then read it back when the 
program starts
again.

Thanks,
Jon.