[plt-scheme] Fraction printing and plots in repl

Hi all,

I'd like to know, how DrScheme achieves the fraction pretty printing in
the repl. Can I use the same method to pretty print, any other object,
in a textbox, or canvas?
Can I make a plot show up in a canvas?

Cheers,
-- 

Paulo J. Matos : pocm [_at_] mega . ist . utl . pt
Instituto Superior Tecnico - Lisbon
Computer and Software Eng. - A.I.
 - > http://mega.ist.utl.pt/~pocm
---
        -> God had a deadline...
                So, he wrote it all in Lisp!