There’s a simple way to write the Elixir and Erlang codes under the same umbrella project and you can use them together.

1. Create a new umbrella project

For this example, I’ll create an umbrella project.

$> mix new ping_beam --umbrella
$> cd ping_beam
$> tree
.
├── apps
├── config
│  └── config.exs
├── mix.exs
└── README.md

2. Create an Elixir project in umbrella

I’ll start off by creating an Elixir project inside the apps folder.

$> mix new ping_elixir

Now, I’ll add a ping function inside the PingElixir module whose only purpose is to print out a message.

# apps/ping_elixir/lib/ping_elixir.ex
defmodule PingElixir do
  @moduledoc false

  def ping do
    IO.puts("Ping from Elixir")
  end
end

3. Create an Erlang project in umbrella

I’ll create an Erlang project using rebar3 also inside the apps folder.

$> rebar3 new lib ping_erlang

As for the Elixir project, I’ll also create a module and add a ping function there.

% apps/ping_erlang/src/ping_erlang.erl
-module(ping_erlang).

-export([ping/0]).

ping() -> <<"Ping from Erlang">>.

4. Reference and use the projects above

For this step, I’ll create a new project named ping where I’ll create a ping function and call the modules above.

$> mix new ping

Now, I’ll change the mix.exs adding the PingElixir and ping_erlang modules as umbrella dependencies.

# apps/ping/mix.exs
defmodule Ping.MixProject do
  # project config...

  defp deps do
    [
      {:ping_elixir, in_umbrella: true},
      # As the Erlang project, it's really important to add the manager as rebar3
      {:ping_erlang, in_umbrella: true, manager: :rebar3}
    ]
  end
end

After that, I’ll modify the ping module to call those modules.

# apps/ping/lib/ping.ex
defmodule Ping do
  @moduledoc false

  def ping do
    [
      PingElixir.ping(),
      :ping_erlang.ping()
    ]
  end
end

5. Running

And as for the testing of the code, it’s pretty simple.

$> iex -S mix

iex> PingElixir.ping()
"Ping from Elixir"

iex> :ping_erlang.ping()
"Ping from Erlang"

iex> Ping.ping()
["Ping from Elixir", "Ping from Erlang"]

6. Conclusion

It’s a really simple process! Just put the Elixir and Erlang codes together. And with a few lines of code, you’ll get it done.

Check the repo for more.

Thanks!