可以安全地忽略宏和内置函数之间的区别吗？ [英] Can one safely ignore the difference between a macro and a built-in?

问题描述

我从Clojure开始，这也是我的第一个lisp。显然有很多东西需要接受，为了减轻认知负荷，我尝试找到我可以放心忽略的部分（现在）。

I'm starting out with Clojure, which is also my first lisp. There's obviously a lot to take in, and in an attempt to lessen the cognitive load, I try to find the parts which I can safely ignore (for now).

一个安全地处理具有宏的表单和内置的表单相同，或有陷阱会后来弹出？

Can one safely treat forms with macros and forms with built-ins the same, or are there pitfalls that will spring up later?

换句话说，我会遇到一个情况，我需要知道（defn f1 []）扩展为

In other words, will I ever run into a situation where I need to know that (defn f1 []) expands to

(def f1 (.withMeta (clojure.core/fn f1 ([])) (.meta (var f1))))

推荐答案

宏在一般情况下是非常不同的。宏不是头等公民：你不能将它们传递给 map 等，你不能将它们存储在变量中，你不能将应用到参数列表。最初，你不需要担心这些，因为他们会显然不工作：一个微妙的，难以察觉的错误将是一个更麻烦。如果尝试运行

Macros in general compose very differently. Macros are not "first class citizens": you can't pass them to map etc., you can't store them in variables and you can't apply them to a list of arguments. Initially you don't need to worry about these because they will obviously not work: a subtle, hard-to-detect error would be a lot more troubling. If you try to run

(map if [true false true false] [1 2 3 4] [-1 -2 -3 -4])

这是事实，如果不是函数变得非常明显。只要记住，宏不是函数，你应该很好：）

the fact that if is not a function will become very apparent. Just keep in mind that macros are not functions and you should be just fine :)

PS：宏是（fn（fn D）：^ P）：O）

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