Is an R environment an ancestor of another

ancestor.R

# test if env has parent
has_ancestor <- function(env, ancestor, last = global_env(), n = NULL) {
  # special cases
  if (!typeof(env) == "environment") {
    abort("`env` must be an environment")
  }
  if (is_empty_env(env)) {
    return(FALSE)
  }
  if (!typeof(ancestor) %in% c("environment", "NULL")) {
    abort("`ancestor` must be `NULL` or an environment")
  }  
  if (is_empty_env(ancestor) || is.null(ancestor)) {
    return(TRUE)
  }
  if (is_reference(env, ancestor)) {
    return(TRUE)
  }

  if (!typeof(last) %in% c("environment", "NULL")) {
    abort("`last` must be `NULL` or an environment")
  }
  if (!is.null(n) || is_scalar_integerish(n)) {
    abort("`n` must be a scalar integer or `NULL`")
  }
  n <- n %||% env_depth(env)
  if (n < 0L) {
    abort("`n` must be an integer greater than or equal to zero")
  }
  i <- 0L
  while (TRUE) {
    i <- i + 1L
    # reached maximum depth
    if (i > n) {
      return(FALSE)
    }
    parent <- env_parent(env)    
    # found an ancestor!
    if (is_reference(parent, ancestor)) {
      return(TRUE)
    }
    # reached last environment    
    if (is_reference(parent, last) || is_empty_env(parent)) {
      return(FALSE)
    }
    env <- parent
  }
}
has_ancestor(bottom, top)