匿名函数简写 [英] Anonymous function shorthand

问题描述

关于使用短符号 #(..) 的匿名函数，我有些不明白

There's something I don't understand about anonymous functions using the short notation #(..)

以下工作:

REPL>  ((fn [s] s) "Eh")
"Eh"

但这不会:

REPL>  (#(%) "Eh")

这有效:

REPL> (#(str %) "Eh")
"Eh"

我不明白的是为什么 (#(%) "Eh") 不起作用，同时我不需要使用 str 在 ((fn [s] s) "Eh")

What I don't understand is why (#(%) "Eh") doesn't work and at the same time I don't need to use str in ((fn [s] s) "Eh")

它们都是匿名函数，而且它们都采用一个参数.为什么速记符号需要函数而其他符号不需要?

They're both anonymous functions and they both take, here, one parameter. Why does the shorthand notation need a function while the other notation doesn't?

推荐答案

#(...)

是

(fn [arg1 arg2 ...] (...))

(其中 argN 的数量取决于您在体内有多少 %N).所以当你写:

(where the number of argN depends on how many %N you have in the body). So when you write:

#(%)

翻译成:

(fn [arg1] (arg1))

请注意，这与您的第一个匿名函数不同，例如:

Notice that this is different from your first anonymous function, which is like:

(fn [arg1] arg1)

您的版本将 arg1 作为值返回，来自扩展速记的版本尝试将其作为函数调用.由于字符串不是有效函数，您会收到错误消息.

Your version returns arg1 as a value, the version that comes from expanding the shorthand tries to call it as a function. You get an error because a string is not a valid function.

由于简写在正文周围提供了一组括号，因此它只能用于执行单个函数调用或特殊形式.

Since the shorthand supplies a set of parentheses around the body, it can only be used to execute a single function call or special form.

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