Calling an R function in a different environment

Question

I fell like it should be fairly straightforward to do this, but I can't for the life of me find a solution... I want to evaluate an R function in an environment different from the one where it is.

What I'd like:

# A simple function
f <- function() {
  x + 1
}

# Create an env and assign x <- 3
env <- new.env()
assign("x", 3, envir = env)

# Call f on env
call_on_env(f, env)
#> 4

The closest I got to "call_on_env()" was:

# Quote call and evaluate
quo <- quote(f())
eval(quo, envir = env)

Unfortunately the code above returns an error: Error in f() : object 'x' not found. So then... Is there a way for me to evaluate f() on env?

Edit: I'm able to send f() to env and then call it, but this leaves f() permanently there. For context [see below], I want to call the function in parallel with some pre-loaded packages.

Context: I'm calling a function in parallel with parallel::clusterMap() and I'd like for the packages loaded in my global environment to also be loaded on the clusters. As far as I can tell, parallel::clusterExport() can only export a list of variables, so it doesn't work for me...

Answer 1

Move f into env

environment(f) <- env
f()
# [1] 4

Note: Evaluation of objects across different environments is not desirable, as you have encountered here. It's best to keep all objects that you plan to interact with one another in the same environment.

If you don't want to change the environment of f, you could put all the above into a new function.

fx <- function(f, env) {
    environment(f) <- env
    f()
}
fx(f, env)
# [1] 4