def eval_input input
    [loop_eval(input), nil]
  rescue SystemExit
    throw(:rib_exit, input)
  rescue Exception => e
    [nil, e]
  ensure
    config[:line] += 1
  end
def eval_input input
    [loop_eval(input), nil]
  rescue SystemExit
    throw(:rib_exit, input)
  rescue Exception => e
    [nil, e]
  ensure
    config[:line] += 1
  end
Evaluate the input using #loop_eval and handle it