[R-SIG-Mac] Scoping question

[Simon Urbanek]

Peter,

this is a list for Mac-related issues. Please use R-help for general  
questions for help - or actually just read about the difference  
between lexical and dynamic scoping (R uses the former which means  
that f will be evaluated in the global environment so there will be no  
foobar).

Cheers,
Simon


On Apr 14, 2009, at 12:08 , iuhz7j202 at sneakemail.com wrote:

> 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
>
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