为什么在Clojure中从catch部分重现是非法的

Question

至少有one answered question关于异常的重复。我的问题是为什么Clojure编译器不接受2 2 1

recur

错误“只能从尾部位置重现”。

根据控制流程，此(loop [] (try (catch Exception _ex (recur)))) 位于尾部位置，因为代码在recur形式recur之后不执行任何操作。

Answer 1

如果在询问“为什么会这样？”，您要求提供历史记录，您可以在clojure@googlegroups.com的Clojure邮件列表中找到更好的答案。我怀疑原因是编译器作者从未考虑过这个用例。

您可以轻松地模拟您想要的行为，如此示例所示。它没有像上一个问题中的大多数答案那样使用宏：

    (loop [count 5]
      (newline)
      (println "top of loop; count=" count)
      (let [caught-ex (try
                        (println "in try")
                        (/ 1 0)
                        false
                        (catch Exception ex
                          (println "   in catch; count=" count "   cause:  " (.getMessage ex))
                          true))]
           (when (and caught-ex
                   (pos? count))
             (recur (dec count)))))

结果：

top of loop; count= 5
in try
   in catch; count= 5    cause:   Divide by zero

top of loop; count= 4
in try
   in catch; count= 4    cause:   Divide by zero

top of loop; count= 3
in try
   in catch; count= 3    cause:   Divide by zero

top of loop; count= 2
in try
   in catch; count= 2    cause:   Divide by zero

top of loop; count= 1
in try
   in catch; count= 1    cause:   Divide by zero

top of loop; count= 0
in try
   in catch; count= 0    cause:   Divide by zero