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问题描述
我想要一个宏my-macro
,它可以扩展为1 2 3
而不是(1 2 3)
,这样
I want a macro my-macro
which can expand to 1 2 3
rather than (1 2 3)
, so that
(list (my-macro) 4 5) -> (1 2 3 4 5)
这可能吗?
推荐答案
否,宏不能扩展为多个值.当您需要将宏扩展为多段代码时,通常要做的就是将返回值包装在progn
中.
No, macros cannot expand to more than one value. The typical thing to do when you need a macro to expand to multiple pieces of code is to wrap the return value in a progn
.
在注释的示例中,看起来好像您不是将宏用作语法抽象,而是将其作为廉价而愉悦的函数优化来使用,通常的响应是请不要这样做,这是错误的"并没有真正做到你想要的".
In your example in the comments, it looks as if you are using macros not as syntactic abstractions, but as cheap-and-cheerful function optimizations, the usual response to that is "please don't do it, it is wrong and doesn't actually do what you want".
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