为什么在宏中用哈希符号结束变量? [英] Why end variables with hash symbol in macros?
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问题描述
I was looking clojure.core
's macro implementation of and
and I noticed that some of the let
bindings in this source file's macros end their variable name with and octothorpe (#
).
进一步检查时,请使用以下代码...
Upon further inspection with the following code...
(defn foo# [] 42)
(foo#) ; => 42
...我意识到octothorpe只是一个有效的符号(至少在结尾处包含了该符号).
...I realized that octothorpe is just a valid symbol (at least when included on the end).
所以,我的问题是,为什么这些核心宏以哈希字符结尾它们的绑定符号?我在这里缺少某些特定的隐含含义或约定吗?
So, my question is, why do these core macros end their binding symbols with a hash character? Is there some specific implied meaning or convention I am missing here?
推荐答案
The # at the end of a symbol is interpreted specially by the reader as a shortcut for gensym.
(gensym "foo")
;=> foo3
(defmacro hygienic []
`(let [foo# 42] foo#))
(hygienic)
;=> 42
(macroexpand '(hygienic))
;=> (let* [foo__1__auto__ 42] foo__1__auto__)
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