Token cache closure

token.R

tokens_pool <- function(tokens){
  current_count <- 1
  list(get_next_token = function(){
    current_count <<- current_count +1
    if(current_count>length(tokens)){
      current_count <<- 1
    }
    return(tokens[[current_count]])
  },
  get_current_token = function(){
    return(tokens[[current_count]])
  }
  )
}