# Creating modules in Julia v0.7-alpha

**URL:** <https://discourse.julialang.org/t/creating-modules-in-julia-v0-7-alpha/11475>\
**Category:** General Usage\
**Created:** [June 6, 2018, 2:40pm UTC](https://discourse.julialang.org/t/creating-modules-in-julia-v0-7-alpha/11475 "2018-06-06T14:40:01Z")\
**Posts on this page:** 13\
**Page:** 1

<div class="post-metadata">

**Author:** ![dlfivefifty](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/dlfivefifty/32/1959_2.png) [@dlfivefifty](https://discourse.julialang.org/u/dlfivefifty)\
**Post date:** [June 6, 2018, 2:40pm UTC](https://discourse.julialang.org/t/creating-modules-in-julia-v0-7-alpha/11475/1 "2018-06-06T14:40:01Z")

</div>

I’m very confused on how to create a new module in Julia v0.7. Even the following doesn’t work:

```julia
julia> module Foo
       end
Main.Foo

julia> using Foo
ERROR: ArgumentError: Module Foo not found in current path.
Run `Pkg.add("Foo")` to install the Foo package.
Stacktrace:
 [1] require(::Module, ::Symbol) at ./loading.jl:868

```

Another issue: I have a new package `Foo` I’ve created with file `.julia/dev/Foo/src/Foo.jl` consisting of:

```julia
module Foo
using Base
# using LinearAlgebra
end

```

This works fine. But if I uncomment `using LinearAlgebra` I get the error:

```julia

julia> using Foo
ERROR: LoadError: ArgumentError: Module LinearAlgebra not found in current path.
Run `Pkg.add("LinearAlgebra")` to install the LinearAlgebra package.
Stacktrace:
 [1] require(::Module, ::Symbol) at ./loading.jl:868
 [2] include at ./boot.jl:314 [inlined]
 [3] include_relative(::Module, ::String) at ./loading.jl:1071
 [4] _require(::Base.PkgId) at ./loading.jl:997
 [5] require(::Base.PkgId) at ./loading.jl:878
 [6] require(::Module, ::Symbol) at ./loading.jl:873
in expression starting at /Users/sheehanolver/.julia/dev/Foo/src/Foo.jl:3

```

Even though other packages I have installed also call `using LinearAlgebra`.

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<div class="post-metadata">

**Author:** ![dlfivefifty](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/dlfivefifty/32/1959_2.png) [@dlfivefifty](https://discourse.julialang.org/u/dlfivefifty)\
**Post date:** [June 6, 2018, 2:50pm UTC](https://discourse.julialang.org/t/creating-modules-in-julia-v0-7-alpha/11475/2 "2018-06-06T14:50:46Z")

</div>

An update: I sort of figured out how to solve the second problem:

1. Delete all references to Foo.jl in .julia
2. In a new location, run `generate Foo` in Pkg mode
3. cd into the new Foo directory
4. Call `add LinearAlgebra` in Pkg mode
5. Copy-and-paste the existing src code that called `using LinearAlgebra` inside of Foo
6. ^D out of julia so it forgets I ever ran `using Foo` (how dare I!!)
7. Open a new julia session
8. cd again into the new Foo directory
9. Now call `using Foo` and it works!
10. There is no step 10

I haven’t figured out how to get `using Foo` to work without first cding into its directory… make a link in `.julia/dev` didn’t work.

---

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**Author:** ![Roger-luo](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/roger-luo/32/3399_2.png) [@Roger-luo](https://discourse.julialang.org/u/Roger-luo)\
**Post date:** [June 6, 2018, 2:56pm UTC](https://discourse.julialang.org/t/creating-modules-in-julia-v0-7-alpha/11475/3 "2018-06-06T14:56:05Z")

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It actually not related to the version. When you create a module in current scope, you need to load it as a local module:

```julia
module Foo
end

using .Foo

```

or just use its full path

```julia
using Main.Foo

```

---

<div class="post-metadata">

**Author:** ![dlfivefifty](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/dlfivefifty/32/1959_2.png) [@dlfivefifty](https://discourse.julialang.org/u/dlfivefifty)\
**Post date:** [June 6, 2018, 3:02pm UTC](https://discourse.julialang.org/t/creating-modules-in-julia-v0-7-alpha/11475/4 "2018-06-06T15:02:46Z")

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> It actually not related to the version

Not sure what you mean, this is definitely new to Julia v0.7:

```julia
julia> versioninfo()
Julia Version 0.6.2
Commit d386e40c17 (2017-12-13 18:08 UTC)
Platform Info:
  OS: macOS (x86_64-apple-darwin17.3.0)
  CPU: Intel(R) Core(TM) i5-7600K CPU @ 3.80GHz
  WORD_SIZE: 64
  BLAS: libgfortblas
  LAPACK: liblapack
  LIBM: libopenlibm
  LLVM: libLLVM-3.9.1 (ORCJIT, broadwell)

julia> module Foo end
Foo

julia> using Foo 

julia> 

```

---

<div class="post-metadata">

**Author:** ![Roger-luo](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/roger-luo/32/3399_2.png) [@Roger-luo](https://discourse.julialang.org/u/Roger-luo)\
**Post date:** [June 6, 2018, 3:09pm UTC](https://discourse.julialang.org/t/creating-modules-in-julia-v0-7-alpha/11475/5 "2018-06-06T15:09:29Z")

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Oh, sorry, didn’t notice this, I was wrong. I think this is about make things consistent.

in julia, everything is evaluated in module `Main`, and if the module is defined inside it, it should either  
provide a relative path or an absolute path. In v0.6 if you define a module by yourself

```julia
module Foo

module Foo2
end

using Foo2
end

```

this will be wrong. You should use

```julia
module Foo

module Foo2
end

using .Foo2
end

```

and in REPL, what you write is actually inside module `Main`, therefore, it should use relative path or absolute path.

---

<div class="post-metadata">

**Author:** ![dlfivefifty](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/dlfivefifty/32/1959_2.png) [@dlfivefifty](https://discourse.julialang.org/u/dlfivefifty)\
**Post date:** [June 6, 2018, 7:03pm UTC](https://discourse.julialang.org/t/creating-modules-in-julia-v0-7-alpha/11475/6 "2018-06-06T19:03:48Z")

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OK, I think I figured it out:

```julia
(v0.7) pkg> add /path/to/Foo.jl

(v0.7) pkg> develop /path/to/Foo.jl

```

Then I can call `using Foo` without being in the right directory.

---

<div class="post-metadata">

**Author:** ![kristoffer.carlsson](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/kristoffer.carlsson/32/22_2.png) [@kristoffer.carlsson](https://discourse.julialang.org/u/kristoffer.carlsson)\
**Post date:** [June 6, 2018, 10:01pm UTC](https://discourse.julialang.org/t/creating-modules-in-julia-v0-7-alpha/11475/7 "2018-06-06T22:01:15Z")

</div>

Should be no need to `add` first.

---

<div class="post-metadata">

**Author:** ![PetrKryslUCSD](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/petrkryslucsd/32/215825_2.png) [@PetrKryslUCSD](https://discourse.julialang.org/u/PetrKryslUCSD)\
**Post date:** [June 6, 2018, 11:57pm UTC](https://discourse.julialang.org/t/creating-modules-in-julia-v0-7-alpha/11475/8 "2018-06-06T23:57:50Z")

</div>

Why do you think it would be better to do `pkg> develop /path/to/Foo.jl` rather than `pkg> add /path/to/Foo.jl`? (I am just trying to understand the philosophy of the package manager.) Thanks.

---

<div class="post-metadata">

**Author:** ![kristoffer.carlsson](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/kristoffer.carlsson/32/22_2.png) [@kristoffer.carlsson](https://discourse.julialang.org/u/kristoffer.carlsson)\
**Post date:** [June 7, 2018, 6:57am UTC](https://discourse.julialang.org/t/creating-modules-in-julia-v0-7-alpha/11475/9 "2018-06-07T06:57:31Z")

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The way `add local_repo_path#branch` works is exactly the same as `add external_repo_url#branch`. Track the git repository at the path / url and use `update` to get new commits on the branch you track.  
Note that only using `add` means that your project has an immutable state and will work the same whenever you get back to it.

`dev` is used when you want to point to a path and use the (mutable) state of the files there. There is no longer any guarantee that the project will work the same next time you get back to it, the files are no longer considered immutable and might have been changed since last time you used the project.

---

<div class="post-metadata">

**Author:** ![dlfivefifty](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/dlfivefifty/32/1959_2.png) [@dlfivefifty](https://discourse.julialang.org/u/dlfivefifty)\
**Post date:** [June 7, 2018, 7:01am UTC](https://discourse.julialang.org/t/creating-modules-in-julia-v0-7-alpha/11475/10 "2018-06-07T07:01:15Z")

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How does it choose which version to use? I.e. the one in dev/ vs one in packages/?

---

<div class="post-metadata">

**Author:** ![kristoffer.carlsson](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/kristoffer.carlsson/32/22_2.png) [@kristoffer.carlsson](https://discourse.julialang.org/u/kristoffer.carlsson)\
**Post date:** [June 7, 2018, 7:05am UTC](https://discourse.julialang.org/t/creating-modules-in-julia-v0-7-alpha/11475/11 "2018-06-07T07:05:02Z")

</div>

If the manifest has a `path` entry it uses that path. If the manifest does not have a `path` entry the path is computed based on `git-tree-sha` and is loaded from `packages`. `dev` puts a path entry into the Manifest.

---

<div class="post-metadata">

**Author:** ![dlfivefifty](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/dlfivefifty/32/1959_2.png) [@dlfivefifty](https://discourse.julialang.org/u/dlfivefifty)\
**Post date:** [June 7, 2018, 8:44am UTC](https://discourse.julialang.org/t/creating-modules-in-julia-v0-7-alpha/11475/12 "2018-06-07T08:44:09Z")

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OK, I think I understand. `.julia/environments/v0.7` is the default “project”, but is otherwise treated the same as all other projects. If I was stubborn and wanted to manage the packages available by hand, I would need to edit Manifest.toml by adding

```julia
[[Foo]]
deps = ["LinearAlgebra"]
path = "/path/to/Foo.jl"
uuid = "?????"
version = "0.0.0"

```

Where I would somehow need to figure out the UUID of Foo.jl. What typing

```julia
(v0.7) pkg> develop /path/to/Foo.jl

```

does is adds these lines, with the correct UUID, to Manifest.toml

Ojn the other hand,

```julia
(v0.7) pkg> add BenchmarkTools

```

just adds

```julia
[[BenchmarkTools]]
deps = ["Compat", "JSON"]
git-tree-sha1 = "ea054fbc1f71dd1544b0c4dc5623e059aba288c0"
uuid = "6e4b80f9-dd63-53aa-95a3-0cdb28fa8baf"
version = "0.3.1"

```

that is, it doesn’t specify a path, so instead of loading from the specified path, it loads from `.julia/packages/`, using the UUID and version to choose the right package. If then type

```julia
(v0.7) pkg> develop BenchmarkTools

```

it clones BenchmarkTools.jl to `.julia/dev/BenchmarkTools`, and modifies Manifest.toml by adding `path = ~/.julia/dev/BenchmarkTools`, so `using BenchmarkTools` looks for the package at the specified path.

---

<div class="post-metadata">

**Author:** ![kristoffer.carlsson](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/kristoffer.carlsson/32/22_2.png) [@kristoffer.carlsson](https://discourse.julialang.org/u/kristoffer.carlsson)\
**Post date:** [June 7, 2018, 11:56am UTC](https://discourse.julialang.org/t/creating-modules-in-julia-v0-7-alpha/11475/13 "2018-06-07T11:56:15Z")

</div>

Yes, good summary.