r - Limiting variable scope

Question

I'm trying to write a function, which limits the scope of R variables. For example,

source("LimitScope.R")
y = 0
f = function(){
   #Raises an error as y is a global variable
   x = y
}

I thought of testing the variable environment, but wasn't really sure of how to do this.

The why

I teach R to undergrads. In their first couple of practicals a few of them always forget about variable scope, so their submitted functions don't work. For example, I always get something like:

n = 10
f = function(x){
  #Raises an error
  #as I just source f and test it for a few test cases.
  return(x*n)
}

I was after a quick function that would 'turn off' scope. As you can imagine it doesn't have to be particularly robust, as it would just be offered for the few practicals.

Answer 1

I'm not sure that you want to do this in general, but the local() function should help, as should the codetools library.

In your example, try

f = local( function() { ... }, baseenv())

It does not do exactly what you want, but it should get you closer.