Clojure得到本地让 [英] Clojure get local lets

问题描述

如何获取使用let定义的局部变量的映射？

How can you get a map of the local variables defined using let?

(let [foo 1] (println (get (get-thread-bindings) "foo")))
; prints nil

还有另外一个功能吗？还是有一种方法从get-thread-bindings映射中提取变量？任何解决方案都应该使用嵌套的let语句。

Is there another function that does this? Or is there a way to extract the variables from the get-thread-bindings map? Any solution should work with nested let statements as well.

推荐答案

正如评论中的链接所指出的， code>& env 变量 defmacro 。根据文档：

As pointed out in the link in the comments, there's a special &env variable available inside defmacro. Per the documentation:

在defmacro中有两个特殊变量，用于更高级的
用法：

Two special variables are available inside defmacro for more advanced usages:

• & form - 数据）


• & env - 宏扩展点的本地绑定映射。 env映射
  是从符号到包含关于
  绑定的编译器信息的对象。

您可以使用此宏来编写一个宏，该宏将扩展为在扩展点处为您提供本地绑定的映射：

You can use this to write a macro that will expand to give you a mapping of local bindings at the point where the macro is expanded:

(defmacro get-env
  []
  (into {} (for [k (keys &env)]
             [(name k) k])))

这扩展为符号名称（name k）到符号 k 用于所有本地绑定（keys& env）

This expands as a map of symbol name (name k) to symbol k for all local bindings (keys &env) which, when evaluated, will give a map of symbol name to current binding for the symbol.

 user> (get-env) ; => {}
 user> (let [a 1] (get-env)) ; => {"a" 1}
 user> (let [a 1 b 2]
         (let [b 3 c 4] (get-env))) ; => {"c" 4, "b" 3, "a" 1}

参数：

 user> (defn foo [x] (let [y 1] (get-env)))
 user> (foo 2) ; => {"y" 1, "x" 2}

这篇关于Clojure得到本地让的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！