# Internal representation of \`using Foo\`
**URL:** https://discourse.julialang.org/t/internal-representation-of-using-foo/19771
**Category:** Internals & Design
**Created:** [January 18, 2019, 8:09am UTC](https://discourse.julialang.org/t/internal-representation-of-using-foo/19771 "2019-01-18T08:09:52Z")
**Posts on this page:** 5
**Page:** 1
### Author:  [@hhaensel](https://discourse.julialang.org/u/hhaensel)
#### Post date: [January 18, 2019, 8:09am UTC](https://discourse.julialang.org/t/internal-representation-of-using-foo/19771/1 "2019-01-18T08:09:52Z")
When trying to make Lint.jl working in Juno with Julia 1.0.1, I realised that Lint would stumble across any line with `using [...]`.
Digging into the root cause I found that `dump(:(using Foo))` has different results in different Julia versions:
```julia
julia-0.6.2.2> dump(:(using Foo))
Expr
head: Symbol using
args: Array{Any}((1,))
1: Symbol Foo
typ: Any
```
```julia
julia-1.0.1> dump(:(using Foo))
Expr
head: Symbol using
args: Array{Any}((1,))
1: Expr
head: Symbol .
args: Array{Any}((1,))
1: Symbol Foo
```
Is this by purpose? It seems a bit odd, as
```julia
julia-1.0.1> Expr(:using,:Foo)
:(using Foo)
```
but
```julia
julia-1.0.1> dump(Expr(:using,:Foo))
Expr
head: Symbol using
args: Array{Any}((1,))
1: Symbol Foo
```
Maybe, I have missed something?
---
### Author:  [@Tamas\_Papp](https://discourse.julialang.org/u/Tamas_Papp)
#### Post date: [January 18, 2019, 9:46am UTC](https://discourse.julialang.org/t/internal-representation-of-using-foo/19771/2 "2019-01-18T09:46:28Z")
> [@hhaensel](#):
>
> Is this by purpose?
The AST representation of various things was not stable prior to 1.0.
---
### Author:  [@hhaensel](https://discourse.julialang.org/u/hhaensel)
#### Post date: [January 18, 2019, 10:32am UTC](https://discourse.julialang.org/t/internal-representation-of-using-foo/19771/3 "2019-01-18T10:32:56Z")
My concern is not so much the stability of AST between Julia versions, it is more that the output of `dump(Expr(:using,:Foo))` is not identical to `dump(:(using Foo))` although `Expr(:using,:Foo)` evaluates to `:(using Foo)`.
Funny enough, `dump(Expr(:using,:Foo)) == dump(:(using Foo))` evaluates to `true` …
---
### Author:  [@Tamas\_Papp](https://discourse.julialang.org/u/Tamas_Papp)
#### Post date: [January 18, 2019, 10:53am UTC](https://discourse.julialang.org/t/internal-representation-of-using-foo/19771/4 "2019-01-18T10:53:45Z")
The expression type for using is [undocumented](https://docs.julialang.org/en/v1.2-dev/devdocs/ast/#Expr-types-1), you should consider opening an issue.
---
### Author:  [@jeff.bezanson](https://discourse.julialang.org/u/jeff.bezanson)
#### Post date: [January 21, 2019, 10:36pm UTC](https://discourse.julialang.org/t/internal-representation-of-using-foo/19771/5 "2019-01-21T22:36:26Z")
Yes, this representation is intentional. The idea is that the `Expr` with head `.` is a “path expression”, a dot-delimited list of names giving the components of a module path. In general:
```julia
julia> dump(:(using A.B.C.D))
Expr
head: Symbol using
args: Array{Any}((1,))
1: Expr
head: Symbol .
args: Array{Any}((4,))
1: Symbol A
2: Symbol B
3: Symbol C
4: Symbol D
```
So for `using A` the dot expression has a single argument.
Indeed there are a couple rough edges to fix here:
- The printing for `Expr(:using, :Foo)` should use that input form instead of `using Foo`, since as you note they don’t match.
- This should be added to the AST devdocs.
- There should be an error for evaluating `Expr(:using, :Foo)`, or perhaps we should treat it the same as `using Foo`.
> [@hhaensel](#):
>
> Funny enough, `dump(Expr(:using,:Foo)) == dump(:(using Foo))` evaluates to `true`
That would be because `dump` always returns `nothing`! 🙂