Clojure可以通过宏生成函数吗？ [英] Can Clojure generate function by macro?

问题描述

我想通过宏生成fn。但我遇到一个奇怪的问题。
代码在这里。

I'm trying to generator fn through macro.But I meet a strange issue. Code is Here.

(defmacro test2 [lmk]
   (fn [lmk2] (println lmk lmk2)))
((test2 12) 13) ;;----->Error
(defmacro test3 []
   (fn [lmk] (println lmk)))
((test3) 12) ;;----->OK
(defmacro test4 []
   `(fn [lmk] (println lmk)))
((test4) 12) ;;----->Error

我知道defn可以正常工作。我只是想知道为什么我不能使用defmacro here.And为什么test3工作良好，但test2失败。

I know defn can work well.I just want to know why I can't use defmacro here.And why test3 works well,however test2 fails.

推荐答案

test2，在编译之前，test2宏将被调用（lmk尚未被编译或评估） - 因为没有语法quote，这将实际上评估fn形式并返回一个函数对象（使用lmk closed over）。所以，你的形式（fn-object 13）传递给编译器，我认为这是一个意想不到的路径（不确定是什么）。有趣的是，它的工作原理：

In test2, prior to compilation, the test2 macro will be invoked (lmk has not yet been compiled or evaluated) - because there is no syntax quote, this will actually evaluate the fn form and return a function object (with lmk closed over). So you then have the form (fn-object 13) passed to the compiler, which I think is going down an unexpected path (not sure exactly what that is). Interestingly this works:

(def f (test2 12))
(f 13)

在test4中，语法引用将导致每个lmk符号在命名空间中解析，因此是错误的来源。你真的想要那些自动生成：

In test4, the syntax quote will cause each lmk symbol to be resolved in the namespace so that's the source of that error. You really want autogensyming on those:

(defmacro test4 [] 
  `(fn [lmk#] (println lmk#)))

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