R Style Guides?

Hi:

I am looking for "style guides" for larger R programs,
and would like suggestions of web pages or documents to look at.

I am particularly interested in guidelines for how to structure programs,
and such issues as managing scope, passing data around, data hiding,
and so forth.
I do have some understanding of how scope works, and how
object-oriented programming does or might work.
But I am not looking for more explanations of the detail mechanisms.

What I want is documented advice on how to use these mechanisms
for laying out larger programs, with rationale, and preferably with 
examples.

Suggestions, please?

Thanks
Robert Biddle