# Question on the Design of Macro Hygiene

**URL:** <https://discourse.julialang.org/t/question-on-the-design-of-macro-hygiene/73992>\
**Category:** New to Julia\
**Tags:** macros\
**Created:** [January 3, 2022, 7:01pm UTC](https://discourse.julialang.org/t/question-on-the-design-of-macro-hygiene/73992 "2022-01-03T19:01:31Z")\
**Posts on this page:** 1\
**Showing post:** 5

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**Author:** ![Clement\_Dato](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/clement_dato/32/31364_2.png) [@Clement\_Dato](https://discourse.julialang.org/u/Clement_Dato)\
**Post date:** [January 5, 2022, 8:56pm UTC](https://discourse.julialang.org/t/question-on-the-design-of-macro-hygiene/73992/5 "2022-01-05T20:56:25Z")

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> [@Loop over the variable name inside of function](https://discourse.julialang.org/t/loop-over-the-variable-name-inside-of-function/73868):
>
> Hi, I want to make a simple function with colnames x1, x2, … So I made a below function and realized that “df” should be outside of the function. Why the loop does not work if “df” is inside of the function? I want to make a function including df inside. Could someone help me? Happy new year! \> function ASD(k::Int64) \> df=DataFrame() \> for i in 1:k \> @eval df.$(Symbol("x$i")) = randn(10) \> end \> \> return df \> end a=ASD(2)

This seems like an instance of what I wanted to talk about as problem. The `eval` searches for `df` from the global scope. Admittedly this might not be the best usage of `eval` but intuitively to users who know not that much detail of its impl, it should have worked (at least that’s my understanding of eval in Lispy things (like Python))  
(Edit: i was wrong, in Python `eval` is also defaulted to global scope, but the workaround (that seems general enough) is to actually specify the scope by adding the output of built in function `locals()`)

Your example of `nexprs`, my first thought being, belongs to the case that needs special treatment. They are to me more like C preprocessor style than the all powerful Lisp macro, emphasizing on the textual part of meta programming. And the users who are calling this macro are obviously actively seeking a shortcut to declare variables (as such, what they want is a textual macro), thus there will be much less confusion.

In contrast, when it comes to eval, upon hearing its functionality, we would have expected it to operate on the expression level. Evaluation of expression at here there should be equivalent to directly running that expression here there. The default behavior of such macro seems natural to comply to such intuition. We should not have needed to change `df` to `Thisfunction.df` or the like to refer the exact same thing.

Another thought is that it is easier to inspect outwards than inwards in scope, due to the arborescent nature of code (the out direction is always unique while the in one is not). It seems better to have the innermost scope information preserved by default. Otherwise it would require hard-coding the inner scope as workaround and thus lose generality and reusability.

That said, am I overlooking something about `eval` or is it just not well designed as built-in macro, or there is some merit in this design choice? I would love to see examples that make me learn more about this.

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