Question

此代码来自Clojure的行动清单3.5。当我尝试运行它时，我收到以下错误：

无法动态绑定非动态var：joy.q /两次

自从这本书被印刷以来，我做错了什么还是Clojure改变了约束规则？

(defn twice [x]
  (println "original function")
  (* 2 x))

(defn call-twice [y]
  (twice y))

(defn with-log [function-to-call log-statement]
  (fn [& args]
    (println log-statement)
    (apply function-to-call args)))

(call-twice 10)

(binding [twice (with-log twice "Calling the twice function")]
  (call-twice 20))

Answer 1

来自binding文档：

从Clojure 1.3开始，vars需要明确标记为^：dynamic才能它们是动态可重新绑定的

所以你需要：

(defn ^:dynamic twice [x]
  (println "original function")
  (* 2 x))

尝试重新绑定非动态时出错

1 个答案: