Clojureのbindingとletの違い

binding_let.clj

(def ^:dynamic foo 10)
(let [foo 9999] (println foo)) ;;=> 9999
(binding [foo 9999] (println foo)) ;;=> 9999

(defn print-foo [] (println foo))
(let [foo 9999] (print-foo)) ;;=> 10
(binding [foo 9999] (print-foo)) ;;=> 9999


;; ふつうにdefするとdynamic varじゃないので怒られる
(def foo 10)
(binding [foo 9999] (print-foo))
IllegalStateException Can't dynamically bind non-dynamic var: user/foo  clojure.lang.Var.pushThreadBindings (Var.java:353)