[R] Defining class as a member of another class

[R_help Help]

Hi,

When I define a new class (through setClass), members defined in
representation argument doesn't seem to like a class. For example, if
I do the following:

setClass("NotWork",representation=(x="zoo"))

It seems to me that representation members will take in only primitive
type to R. Is there any way to stuff a class as a member in another
class? Thank you.

- adschai