    /*
     * Document-method: on_progress
     *
     * call-seq: on_progress = Proc.new {|str| ...}
     *
     * This callback setter allows you to pass a Proc/lambda or any other object that responds to #call.
     *
     * It will pass the caller a chunk of the encode buffer after it's reached it's internal max buffer size (defaults to 8kb).
     * For example, encoding a large object that would normally result in 24288 bytes of data will result in 3 calls to this callback (assuming the 8kb default encode buffer).
     */
    static VALUE rb_yajl_encoder_set_progress_cb(VALUE self, VALUE callback) {