Julia:如何创建一个返回其参数的宏? [英] Julia: How do I create a macro that returns its argument?

问题描述

我的问题与 this 非常相似一个，但有区别.我想创建一个以这种方式运行的宏(或其他):

My question is quite similar to this one, but with a difference. I want to create a macro (or whatever) that behaves this way:

julia> @my-macro x + 2
:(x + 2)

(请注意，x + 2 不是括在引号中).朱莉娅有类似的东西吗?如果没有，我该怎么做?(请详细解释它的工作原理.)

(note that x + 2 is not enclosed in quotes). Is there something like that in Julia? And if there is not, how do I do it? (Please, give a detailed explanation about why it works.)

推荐答案

宏的输入表达式需要被引用，因为宏返回一个表达式，它会被计算，而你想获取表达式本身，因此你需要额外的报价.可以这样引用:

The input expression to the macro needs to be quoted because a macro returns an expression, which are evaluated, while you would like to get the expression itself, hence you need an extra quoting. The quoting can be done as:

macro mymacro(ex)
    Expr(:quote,ex) # this creates an expression that looks like :(:(x + 2))
end
e=@mymacro x + 2 #returns :(x + 2)

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