Day 3 - Mix

Hello Again

The past six month's been hectic at work and it's a pity I had little time for Elixir. And now version 1.4 is out, shame on me. This may not be the case anymore since I'm planning on hijacking some of Elixir greatness to my work mix.

And that's what I'm starting off after the hiatus… Mix


Every language comes encapsulated with a system of culture, tools and idioms. The tooling part is quintessential for developer productivity and happiness. It's really cool to see Elixir developers recognizing that part earlier on and building up a build tool which is known as Mix.

There's a lot of grunt work when kicking off with a project. A lot of meta-work is done for it starting right at the preparation phase. What other libraries do I need?, What happens when I compile?, What about tests?, Works on MY MACHINE!, Where do modules live? are few of the decision that needs love. That gave rise to a lot of tools that automate some of these, decide some of these, and lets you make your own (decisions/automation) in a frameworkish fashion. For Clojure, we have the amazing Leiningen (or the equally great Boot), for Elixir, we have Mix. And that's what I've played with (from) today, so that it in return allows me to play with the rest of the ecosystem in future.

Hello Mix

The answer to those questions above is Mix. Mix is a build tool that lets you create, compile, dependancy-manage Elixir projects.

Let's say we want to create a new Elixir project. We already have Elixir installed and Mix comes with it (thankfully). So all we need to do is, fire up the mix command and do something like mix new HelloMix. And it didn't work! This is because of how cool underscores and lower case letters are for folder names (see the cute little error message there?). Correcting ourselves: mix new hello_mix and it should work fine!

Let's inspect the folder and see what Mix gave me-

├── .gitignore
├── config
│   └── config.exs
├── lib
│   └── hello_mix.ex
├── mix.exs
└── test
    ├── hello_mix_test.exs
    └── test_helper.exs

Well, without any preverification I could tell that mix.exs might just be Mix-s project.clj (i.e. :P), test/ would contain the tests, lib/ would house my modules, and with some verifications I got to know that config/ contains all sorts of configuration maps of the modules I'd be using. I absolutely could not find out what .gitignore or does though, might need to upgrade my google-fu.

Next step would be to inspect the mix.exs file. Here is it-

defmodule HelloMix.Mixfile do
  use Mix.Project

  def project do
    [app: :hello_mix,
     version: "0.1.0",
     elixir: "~> 1.4",
     build_embedded: Mix.env == :prod,
     start_permanent: Mix.env == :prod,
     deps: deps()]

  # Configuration for the OTP application
  # Type "mix help" for more information
  def application do
    # Specify extra applications you'll use from Erlang/Elixir
    [extra_applications: [:logger]]

  # Dependencies can be Hex packages:
  #   {:my_dep, "~> 0.3.0"}
  # Or git/path repositories:
  #   {:my_dep, git: "", tag: "0.1.0"}
  # Type "mix help deps" for more examples and options
  defp deps do

First it's the omnipresent defmodule powered by use Mix.Project. It pimps up the module with Mix.Project induced goodness. There are three sections at play here-

  • project - I hold all the meta-information about what you're going to make. I decide how things get build, what Elixir you use, how to run things basically.
  • application - I ensure what libraries need to get compiled before you compile your own?
  • deps - I manage dependancies, and I'm private!

I think other than the version part, I should leave the application segment alone, for now. Let's play with time a little, there's a lib for that: Timex

Common sense tells me to add a dependancy as a map, and it was correct (erm, no it was not, we're not in Clojure anymore, use Tuple), so let's add {:timex, "~> 3.0"} to our dependancy list so that it looks like:

  defp deps do
    [{:timex, "~> 3.0"}]

I learnt more about versioning from here. Well I would blindly copy the recommended line from the libraries for the time being any way. The comment in mix.exs code was kind enough to let me know of other possibilities (i.e. from git?). Thanks guys.

mix deps.get is the npm install of Mix it seems. Just did that and I intend to play with it in the REPL now. iex -S mix did the trick (python shell anyone?).

One thing I have seen is that I did not have to put anything in the application section of my Mix module, and it looked different from other mix.exs-es that I have seen, luckily I stumbled upon this which explained the reason and the application inference is really cool (although I have never lived a life before it).

If I do a single iex, then I cannot get all the deps goodness I mentioned to Mix, the -S mix takes care of that and gives me an environment where Time<TAB> would autocomplete to Timex. So I can play with it straight away. Let's write something in lib/hello_mix.ex:

defmodule HelloMix do
  @moduledoc """
  Documentation for HelloMix.

  @doc """
  Returns the ISO:Extended format of current time.
  def now do
    {_, right_now} = Timex.format, "{ISO:Extended}"

Now if we iex -S mix and type in, we'll see a formatted string of time.

Aliases, Tasks

mix compile, as the name says, compiles your project, but what if I needed mix c? Aliases to the rescue…

defp aliases do
 [c: "compile"]

And then add aliases: aliases() to the project vector.

Aliases can also have functions defined within the module and work as task, so if, we say, have a hello function, it can run it out with mix hello. The function would be defp hello(_), do: IO.puts "Hello". The first parameter is a list of arguments provided, so if we want to know about the arguments, we can go like:

# Note to self, DO UPDATE the `project` with the `aliases`
defp aliases do
  [c: "compile",
   hello: &hello/1,
   concat: &contact/1]

defp concat(args) do
  |> Enum.reduce(&<>/2)
  |> String.reverser
  |> IO.puts

The way of running tasks defined here is more likely to stay private to the app I am using, since the definitions all go into my own mix.exs. We can make usable by other project task by simple creating a module that uses the Mix.Task behaviour. Such as the one below: (I saved it in and as lib/tasks/concat.ex)

defmodule Mix.Tasks.Concat do
  use Mix.Task

  def run(args) do
    |> Enum.reduce(&<>/2)
    |> String.reverse
    |> IO.puts

If we run mix concat hello world now, it would call the defp version of mix.exs, so let's remove it and run it again and we see a helloworld nicely printed out.

In the examples, they used in lieu of IO.puts by the way :)

I'll be back

There is more to (in fact way more to it seems, what I wrote is nothing) Mix than I brushed in here. The excellent documentation here speaks volumes of it. You can play with environments, tests (all it takes is mix test, and OMG Elixir has doctests, next time!), more control in each of the parts of the module. But I guess from what I just practiced thus far should suffice in me trying to act like I can make projects now with Elixir.

There are a few things though which at this point I am too lazy to google for:

  • Is there any mix init that generates a mix project? (I know it's easy to make one)
  • What about mix install --save akin to the one JS folks to? (i.e. gets me latest version of Timex and updates my mix.exs file?)

I guess I could do those too, however, it's pleasant knowing Mix. I will try to be regular for a change and concentrate a lot more on Elixir than I did last year.

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