doParallel does not recognize functions in global environments with multiple sourcings

Question

I have a quick question with respect to the doParallel package in R. I have an optimize.R file where it contains roughly 18 functions A1, A2, A3, A4, ..., A18 within it, and A18 would basically contain all the functions A1, A2, A3,..., A17. I have another result.R file, where I used import every functions within optimize.R into the Global Environment of RStudio (located on the upper-right corner of RStudio). In addition, within result.R file, I have a function F that calls function E under the loop foreach(..., .export = c(".GlobalEnv")) %dopar% {do something}. Now, in the final.R file (which is the main file), I use source(/C:/Users/[Name]/Desktop/result.R, echo = F). Within final.R, I have a function res that calls function F.

However, when I execute this final.R file, I got the error message: task 1: cannot find variable C , which is weird because C is a function, not a variable. Also, it seems to me the .export = c(".GlobalEnv") fails to work, as function C is already in the Global Environment. Can anyone suggest some ways to overcome this kind of issue? I tried to export

Flow of the 3 files.

final.R file

source(/C:/Users/[Name]/Desktop/result.R, echo = F)
library(doParallel)
registerDoParallel(4)
res <- function(var_x, var_y) {
      best.rev <- foreach(i=1:5, .export = c(".GlobalEnv")) %dopar% {
       F(var_x, var_y)
       do something else
      }
      output <- best.rev  
}

result.R file

source(/C:/Users/[Name]/Desktop/optimize.R, echo = F)

F <- function(var1, var2) {
       E(var1, var2)
       do something else
}

optimize.R file

A1 <- function(x1, x2) {....}
A2 <- function(x1, x3, x4) {...}
A3 <- function(x1, x2, x3) {...}
....
A18 <- function(x1,x2,x3,x4,...,x8) {
      a1 <- A1(x1, x2)
      a2 <- A2(a1, x3, x4)
      a3 <- A3(a1, a2, x3)

      return(list(a1, a2, a3))
}