[R] Warning when trying to access a variable out of scope?

[Duncan Murdoch]

On 03/07/2009 3:28 PM, Greg Snow wrote:
> Does this do what you want?
> 
>> b.test <- 3
>>
>> f <- function(a,b) {
> + a+b.test
> + }
>> f(10,20)
> [1] 13
>> environment(f) <- baseenv()
>>
>> f(10,20)
> Error in f(10, 20) : object 'b.test' not found

Probably not:  it messes up cases where f needs to call functions in the 
global environment, or in stats, or some other package.  It might be 
better to say

environment(f) <- parent.env(globalenv())

but that has problems too.

The question really isn't solvable in R.  Since functions and variables 
aren't very different, and since any non-trivial function needs to make 
use of functions outside itself, just about every function makes use of 
globals.  Usually that's fine, they're globals like "mean". Sometimes 
it's not fine, they're globals like "b.test", which aren't meant to be 
seen.

codetools does a pretty good job of detecting these sorts of errors, but 
there really isn't a foolproof test.

Duncan Murdoch