Clojure:如何在运行时创建函数 [英] Clojure: How to create a function at runtime

问题描述

我想在运行时完全生成一个fn(即名称和arg符号是在运行时确定的，而不是在代码中确定的)实现此目标的最佳方法是什么?

I want to generate a fn totally at runtime (i.e. the name and the arg symbols are decided at runtime, not in code) What's the best way to achieve this ?

例如，如何实现以下功能?

For example how can I implement the following function ?

(defn gen-fn [name arg-symbols body]
...
...

将被这样使用:

(gen-fn "my-func-name" (symbol "x") (symbol "y") (println "this is body. x=" x))

请注意，函数名称，args和主体均未编码，但可以在运行时确定

Note that function name, the args and the body are not coded but can be decided at runtime

推荐答案

(defn gen-fn
  [n as b]
  (let [n        (symbol n)
        as       (vec (map symbol as))
        fn-value (eval `(fn ~n ~as ~b))]
    (intern *ns* n fn-value)))

还有一些用途:

user=> (gen-fn "foo" ["x"] '(do (println x) (println (inc x))))
#'user/foo
user=> (foo 5)
5
6
nil

但是，我不太喜欢这种方法.闻起来真难闻: eval .为什么要在运行时生成全局变量?我看到各种错误的命名空间和其他丑陋的问题不断涌现……

However, I don't really like this approach. It smells really hard: eval. Why do you want to generate globals at runtime? I see various problems with wrong namespaces and other ugly hiccups rising at the horizon...

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