Scoping question

Hi,

I'm struggling with a bit of scoping using the with() function. I  
think it's best explained with an example:
 x <- list(foobar=2)
 f <- function(){foobar*2}
 with(x,f())
This throws an error that 'foobar' does not exist. However if I  
define foobar in the global environment, f will find it whether I  
call it from the global environment or from within x. I have also  
tried using get("foobar",parent.frame()) within f, along with other  
variations, with no success.

I could always just add foobar as an argument to f, but in my actual  
work case foobar is a potentially very large object that is not  
worth making a copy of. (I don't know how much of an effect this  
will actually have on performance). I also just don't like all the  
bookkeeping of having to know which objects in x I am going to need  
in f and passing them all as arguments.

I would appreciate any insight about why the scoping is not working  
as I thought it would, and if there is any way to get around it  
without directly passing arguments to f.

Thank you,
Peter