Elixir comes with a bunch of libraries preinstalled. Some are written in Elixir, and others in Erlang.
The first port of call is http://elixir-lang.org/docs.html, the Elixir documentation. Often you’ll find a built-in library that does what you want.
Next, see if any standard Erlang libraries do what you need. This isn’t a simple task. Visit http://erlang.org/doc/ and look in the left sidebar for Application Groups. There you’ll find libraries sorted by top-level category.
If you find what you’re looking for in either of these places, you’re all set, as all these libraries are already available to your application. But if the built-in libraries don’t contain what you need, you’ll have to add an external dependency.
Package managers: Ruby has RubyGems, Python has pip, Node.js has npm.
And Elixir has hex.
Visit https://hex.pm and search its list of packages that integrate nicely with a mix-based project.
If all else fails, Google and GitHub are your friends. Search for terms such as elixir http client or erlang distributed logger, and you’re likely to turn up the libraries you need.
In our case, we need an HTTP client. We find that Elixir has nothing built in, but hex.pm has a number of HTTP client libraries.
To me, HTTPoison looks like a good option. So how do we include it in our project?
Mix takes the view that all external libraries should be copied into the project’s directory structure. The good news is that it handles all this for us—we just need to list the dependencies, and it does the rest. Remember the mix.exs file at the top level of our project? Here is that original version.
| | defmodule Issues.MixProject do |
| | use Mix.Project |
| | |
| | def project do |
| | [ |
| | app: :issues, |
| | version: "0.1.0", |
| | elixir: "~> 1.6-dev", |
| | start_permanent: Mix.env() == :prod, |
| | deps: deps() |
| | ] |
| | end |
| | |
| | # Run "mix help compile.app" to learn about applications. |
| | def application do |
| | [ |
| | extra_applications: [:logger] |
| | ] |
| | end |
| | |
| | # Run "mix help deps" to learn about dependencies. |
| | defp deps do |
| | [ |
| | # {:dep_from_hexpm, "~> 0.3.0"}, |
| | # {:dep_from_git, git: "https://github.com/elixir-lang/my_dep.git", tag: "0.1.0"}, |
| | ] |
| | end |
| | end |
We add new dependencies to the deps function. As the HTTPoison package is in hex.pm, that’s very simple. We just give the name and the version we want.
| | defp deps do |
| | [ |
| | { :httpoison, "~> 1.0.0" } |
| | ] |
| | end |
In this case, we give the version as "~> 1.0.0". This matches any version of HTTPoison with a major version of 1 and a minor version of 0 or greater. In IEx, type h Version for more details.
Once your mix.exs file is updated, you’re ready to have mix manage your dependencies.
Use mix deps to list the dependencies and their status:
| | $ mix deps |
| | * httpoison (package) |
| | the dependency is not available, run `mix deps.get` |
Download the dependencies with mix deps.get:
| | Resolving Hex dependencies... |
| | Dependency resolution completed: |
| | certifi 2.0.0 |
| | hackney 1.10.1 |
| | httpoison 0.13.0 |
| | idna 5.1.0 |
| | metrics 1.0.1 |
| | mimerl 1.0.2 |
| | ssl_verify_fun 1.1.1 |
| | unicode_util_compat 0.3.1 |
| | * Getting httpoison (Hex package) |
| | Checking package (https://repo.hex.pm/tarballs/httpoison-0.13.0.tar) |
| | Using locally cached package |
| | . . . |
Run mix deps again:
| | * mimerl (Hex package) (rebar3) |
| | locked at 1.0.2 (mimerl) 993f9b0e |
| | the dependency build is outdated, please run "mix deps.compile" |
| | * metrics (Hex package) (rebar3) |
| | locked at 1.0.1 (metrics) 25f094de |
| | the dependency build is outdated, please run "mix deps.compile" |
| | * unicode_util_compat (Hex package) (rebar3) |
| | locked at 0.3.1 (unicode_util_compat) a1f612a7 |
| | the dependency build is outdated, please run "mix deps.compile" |
| | . . . |
| | * httpoison (Hex package) (mix) |
| | locked at 0.9.0 (httpoison) 68187a2d |
| | the dependency build is outdated, please run "mix deps.compile" |
This shows that the HTTPoison library is installed but that it hasn’t yet been compiled. Mix also remembers the exact version of each library it installs in the file mix.lock. This means that at any point in the future you can get the same version of the library you use now.
Don’t worry that the library isn’t compiled—mix will automatically compile it the first time we need it.
If you look at your project tree, you’ll find a new directory called deps containing your dependencies. Note that these dependencies are themselves just projects, so you can browse their source and read their documentation.