Simple C style enum in R.

enum.R

enum <- function(...) {
  nms <- eval(substitute(alist(...)))
  x <- as.list(setNames(seq_along(nms), nms))
  f <- tempfile()
  attach(x, name = f)
  # Cleanup the enum if when the parent frame exists 
  # unless we are in the global environment.
  if (!identical(parent.frame(),  globalenv())) {
    withr::defer(detach(name = f), parent.frame())
  }
  x
}

year <- enum(Jan, Feb, Mar, Apr, May, Jun, Jul, Aug, Sep, Oct, Nov, Dec)
for (month in year) {
  if (month > Aug) {
    print(month)
  }
}
#> [1] 9
#> [1] 10
#> [1] 11
#> [1] 12