R: Scoping error when calling function from script

I am building a large codebase in R that uses vectorization through many nested user-defined functions. These auxiliary functions are, by in large, written in their own R script for debugging and maintenance purposes. I would like to source some of these scripts within a specific environment, without the functions being called into the Global Environment.

I am trying to make the main.R file as clean and understandable as possible, so that there are scripts that do the dirty work behind the scenes.

In the example below, the global environment becomes populated with f_foobar (which is correct), but also f_foo and f_bar once I call the function f_foobar.

Is there an elegant way to house these auxiliary functions (eg f_foo and f_bar) in a temporary environment?

For example, in file_foo.R:

f_foo <- function() {
  return('a')
}

In file_bar.R:

f_bar <- function() {
  return('b')
}

In file_foobar.R:

f_foobar <- function() {
  source('file_foo.R')
  source('file_bar.R')
  
  value_foo <- f_foo()
  value_bar <- f_bar()
  
  c(value_foo, value_bar) %>% return
}

In main.R:

source('file_foobar.R')

main_result <-f_foobar()