Comment by fnordsensei

This would be better for illustrating that object is not overweritten, I think:

  =>(let [object "light"]
  =>  (let [object "darkness"]
  =>    (println (str "God said let there be " object)))
  =>  (println (str "God said let there be " object)))
  God said let there be darkness
  God said let there be light
  nil