# Soft vs Hard Scopes, Macros, and \`@everywhere\`

**URL:** <https://discourse.julialang.org/t/soft-vs-hard-scopes-macros-and-everywhere/47124>\
**Category:** General Usage\
**Tags:** macros, scope\
**Created:** [September 23, 2020, 9:29am UTC](https://discourse.julialang.org/t/soft-vs-hard-scopes-macros-and-everywhere/47124 "2020-09-23T09:29:50Z")\
**Posts on this page:** 4\
**Page:** 1

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**Author:** ![chisquared](https://avatars.discourse-cdn.com/v4/letter/c/87869e/32.png) [@chisquared](https://discourse.julialang.org/u/chisquared)\
**Post date:** [September 23, 2020, 9:29am UTC](https://discourse.julialang.org/t/soft-vs-hard-scopes-macros-and-everywhere/47124/1 "2020-09-23T09:29:50Z")

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I’m reading the section on the manual regarding the scope of variables:

[https://docs.julialang.org/en/v1.5/manual/variables-and-scoping/](https://docs.julialang.org/en/v1.5/manual/variables-and-scoping/)

It says that macros introduce a hard local scope. There is some ambiguity here which confused me a little since there are two ways in which macros enter your code: the first is when you define them, and the second is when you call them.

I assume this table is referring to the definition of macros. However, I am then confused by the following behaviour, which is why I went to the manual:

```julia
julia> module Foo
       using Distributed
       @everywhere x = 1
       f() = print(x)
       end
Main.Foo

julia> Foo.f()
ERROR: UndefVarError: x not defined
Stacktrace:
 [1] f() at ./REPL[1]:4
 [2] top-level scope at REPL[2]:1

```

On the other hand, if you don’t wrap the code in a `module`:

```julia
julia> using Distributed

julia> @everywhere x = 1

julia> f() = print(x)
f (generic function with 1 method)

julia> f()
1

```

This made me think that _calling_ macros introduced a soft local scope. (Though I may have misunderstood the manual here; I’m not convinced I fully understand the distinction yet.) However, this seems special to the `@everywhere` macro.

```julia
julia> module Bar
       @eval x = 1
       f() = print(x)
       end
Main.Bar

julia> Bar.f()
1

```

I’m not really sure what’s going on, and the documentation for [`@everywhere`](https://docs.julialang.org/en/v1/stdlib/Distributed/#Distributed.@everywhere) and [`@eval`](https://docs.julialang.org/en/v1/base/base/#Base.@eval) don’t reveal too much about this.

The behaviour is exactly the same if you put these commands into a `.jl` file and run them using `include`.

Can anyone help explain what’s happening?

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<div class="post-metadata">

**Author:** ![marius311](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/marius311/32/3953_2.png) [@marius311](https://discourse.julialang.org/u/marius311)\
**Post date:** [September 23, 2020, 11:46am UTC](https://discourse.julialang.org/t/soft-vs-hard-scopes-macros-and-everywhere/47124/2 "2020-09-23T11:46:58Z")

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I don’t think its really related to scope. The docs for `@everywhere` actually do give a hint, they say the expression is evaluated under `Main`, so even when `@everywhere x = 1` is inside `Foo`, it sets a variable `x` in the `Main` module.

Depending where you actually want the variable, you could `@everywhere @eval Foo x = 1` to instead set it inside `Foo` (note you need to define the module on the workers too, so put another `@everywhere` around the module definition), or you could `print(Main.x)` instead.

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<div class="post-metadata">

**Author:** ![chisquared](https://avatars.discourse-cdn.com/v4/letter/c/87869e/32.png) [@chisquared](https://discourse.julialang.org/u/chisquared)\
**Post date:** [September 23, 2020, 12:23pm UTC](https://discourse.julialang.org/t/soft-vs-hard-scopes-macros-and-everywhere/47124/3 "2020-09-23T12:23:15Z")

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Aha. And here I thought I read that part carefully.

In a way, it is related to scope: just not local vs global, but it’s about which global scope.

Thanks for the clarification!

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<div class="post-metadata">

**Author:** ![chisquared](https://avatars.discourse-cdn.com/v4/letter/c/87869e/32.png) [@chisquared](https://discourse.julialang.org/u/chisquared)\
**Post date:** [September 23, 2020, 12:23pm UTC](https://discourse.julialang.org/t/soft-vs-hard-scopes-macros-and-everywhere/47124/4 "2020-09-23T12:23:44Z")

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Aha. And here I thought I read that part carefully.

In a way, it is related to scope: just not local vs global, but it’s about which global scope.

Thanks for the clarification!