how to isolate a function

Question

How can I ensure that when a function is called it is not allowed to grab variables from the global environment?

I would like the following code to give me an error. The reason is because I might have mistyped z (I wanted to type y).

z <- 10
temp <- function(x,y) {
        y <- y + 2
        return(x+z)
}
> temp(2,1)
[1] 12

I'm guessing the answer has to do with environments, but I haven't understood those yet.

Is there a way to make my desired behavior default (e.g. by setting an option)?

Answer 1

> library(codetools)
> checkUsage(temp)
<anonymous>: no visible binding for global variable 'z'

The function doesn't change, so no need to check it each time it's used. findGlobals is more general, and a little more cryptic. Something like

Filter(Negate(is.null), eapply(.GlobalEnv, function(elt) {
    if (is.function(elt))
        findGlobals(elt)
}))

could visit all functions in an environment, but if there are several functions then maybe it's time to think about writing a package (it's not that hard).

Answer 2

environment(temp) = baseenv()

See also http://cran.r-project.org/doc/manuals/R-lang.html#Scope-of-variables and ?environment.

Answer 3

environment(fun) = parent.env(environment(fun))

(I'm using 'fun' in place of your function name 'temp' for clarity)

This will remove the "workspace" environment (.GlobalEnv) from the search path and leave everything else (eg all packages).