How to verify if arguments were called, the difficult way

arguments.R

myfunction <- function (a, b, c, ...) 
{
  p <- list()
  # use formals to get the arguments from a function.
  # use sys.function() to get the own function. if you return sys.function() you return itself
  formal.args <- formals(sys.function()) 
  
  formal.args[["..."]] <- NULL # this is not needed, but here you can remove the "..." argument
  
  for (arg in names(formal.args)) {
    # this tests if you pass "" to the argument or if you
    # doesn't call it at all, and remove it from the argument list
    if (as.logical(mget(arg) != "")) { 
      p[arg] <- list(get(arg))
    }
  }
  
  dot.args <- list(...) # you thought you had remove it? You had, but from `formal.args`
  names.dot.args <- names(dot.args)
  # here you add any new argument you got from the `...` and add it as a named argument
  if (length(dot.args) > 0) {
    for (i in 1:length(dot.args)) {
      p[[names.dot.args[i]]] <- dot.args[[i]]
    }
  }
  
  return(p) # just returning something, in this case the arguments that were filtered...
}