local({
  previous_options <- options(warn = 2, digits = 8, stringsAsFactors = FALSE)
  on.exit(options(previous_options), add = TRUE)
  make_counter <- function() {
    value <- 0L
    function() {
      value <<- value + 1L
      value
    }
  }
  a <- make_counter()
  b <- make_counter()
  cat("A:", a(), a(), "B:", b(), "\n")
  invisible(NULL)
})