在Clojure中构造一个匿名函数的映射 [英] Constructing a map on anonymous function in Clojure

问题描述

我只是学习语言，我有一个简单的问题。为什么这样工作（构造 {：keyvalue} ）：

I am just learning the language and I've got a simple question. Why does this work (constructs {:key "value"}):

(#(assoc {} :key %) "value")

：

(#({:key %}) "value")
ArityException Wrong number of args (0) passed to: PersistentArrayMap  clojure.lang.AFn.throwArity (AFn.java:429)

后面的语法是完全有效的：

On Python the latter syntax is perfectly valid:

> (lambda v: {'key': v})('value')
{'key': 'value'}

编辑：感谢伟大的答案，显然我需要停止思考＃等同于 lambda 在Python中。

edit: thanks for great answers, it is apparent I need to stop thinking # as equivalent to lambda in Python.

推荐答案

＃（f％）由（fn [％]（f％））扩展。＃（{：key％}）被扩展为（fn [％]（{：key％}），python等价于 lambda v：{' key'：v}（），它与Clojure版本有相同的问题。

#(f %) is expanded by the reader into (fn [%] (f %). Likewise, #({:key %}) is expanded into (fn [%] ({:key %}). The python equivalent of this would be lambda v: {'key': v}(), which has the exact same problem as the Clojure version.

（fn [v] {：key v}）。如果你真的想使用＃（...）符号，你可以使用＃（do {：key％}）。

What you are looking for is something equivalent to (fn [v] {:key v}). If you really want to use #(...) notation, you could use #(do {:key %}).

code>＃（...）。我认为grok更困难（例如这个证据），并且只是比一个等效的 fn 表单，然后还有＃（...）表单不能嵌套的限制。

Incidentally, I personally never use #(...). I think it's more difficult to grok (as examples such as this evidence), and is only very slightly more compact than an equivalent fn form. Then there's also the limitation that #(...) forms can not be nested.

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