degaray

find_unbound <- function(lang) {
  stopifnot(is.language(lang), !is.expression(lang))

  bound <- character()
  unbound <- character()

  rec_fun <- function(lang) {
    if(is.call(lang)) {
      # These are assignment calls; if any symbols are assigned and have
      # not already been found in a leaf, they are defined as bound