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Elixir Cookbook

Elixir Cookbook

By : Paulo Pereira
4.5 (2)
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Elixir Cookbook

Elixir Cookbook

4.5 (2)
By: Paulo Pereira

Overview of this book

This book is intended for users with some knowledge of the Elixir language syntax and basic data types/structures. Although this is a cookbook and no sequential reading is required, the book’s structure will allow less advanced users who follow it to be gradually exposed to some of Elixir’s features and concepts specific to functional programming. To get the most out of this book, you need to be well versed with Erlang.
Table of Contents (11 chapters)
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Preface
Preface
What this book covers
What you need for this book
Who this book is for
Sections
Conventions
Reader feedback
Customer support
Free Chapter
1
1. Command Line
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1. Command Line
Introduction
Using the terminal to prototype and test ideas
Loading and compiling modules
Getting help and accessing documentation within IEx
Using Erlang from Elixir
Inspecting your system in IEx
Inspecting your system with Observer
Creating a simple application
Managing dependencies
Generating a supervised application
Generating umbrella applications
Managing application configuration
Creating custom Mix tasks
2
2. Data Types and Structures
2. Data Types and Structures
Understanding immutability
Adding and subtracting lists
Combining tuples into a list
Creating and manipulating keyword lists
Using pattern matching
Pattern matching an HTTPoison response
Creating a key/value store with a map
Mapping and reducing enumerables
Generating lazy (even infinite) sequences
Streaming a file as a resource
3
3. Strings and Binaries
3. Strings and Binaries
Introduction
Joining strings
Splitting strings
Replacing string codepoints with patterns
Slicing strings with ranges
Using regular expressions
Combining operations with the |> operator
Creating a word list
Determining the word frequency in a text
Reading and writing metadata from MP3 files
4
4. Modules and Functions
4. Modules and Functions
Introduction
Namespacing modules
Using module attributes as constants
Enforcing behaviors
Documenting modules
Using module directives
Using a module in the scripted mode
Defining functions with default arguments
Using guard clauses and pattern matching in function definitions
5
5. Processes and Nodes
5. Processes and Nodes
Introduction
Sending messages between processes
Making code run on all available CPUs
Using tasks to perform multiple concurrent computations
Creating a stateful server process (messages with counters)
Using agents as an abstraction around states
Using an ETS table to share the state
Creating named nodes
Connecting nodes
Executing code in a different node
6
6. OTP – Open Telecom Platform
6. OTP – Open Telecom Platform
Introduction
Implementing a GenServer
Expanding our server
Creating a supervisor
Using Observer to inspect supervisors and processes
Handling errors and managing exceptions
Packaging and releasing an OTP application
Deploying applications and updating a running system
7
7. Cowboy and Phoenix
7. Cowboy and Phoenix
Introduction
Setting up Cowboy
Serving static files
Implementing a websocket handler
Creating a Phoenix application
Defining routes
Creating a controller
Creating views and templates
Implementing topics
Protecting the Phoenix app with SSL
8
8. Interactions
8. Interactions
Introduction
Using Redis and Postgres
Using OS commands from within Elixir
Getting Twitter data
9
A. Installation and Further Reading
A. Installation and Further Reading
Installing Elixir
Installing PostgreSQL
Installing Redis
Some useful links
10
Index
Index

Managing dependencies

One of the advantages of OTP (more information on OTP may be found in Chapter 6, OTP – Open Telecom Platform) is modularity, and it is very common to have several applications running as dependencies of one application. An application is a way to achieve modularity; in this context, we call an application something that is known in other programming languages as a library. In this recipe, we will integrate an HTTP client with a new application. We will be using the Hex package manager (http://hex.pm).

Getting ready

  1. Generate a new application with mix new manage_deps:
    > mix new manage_deps

    The output is shown in the following screenshot:

    Getting ready
  2. Visit https://hex.pm/packages?search=http.
  3. We will choose HTTPoison (https://hex.pm/packages/httpoison).

How to do it…

To add a dependency to our application, we will follow these steps:

  1. Inside the manage_deps application, open mix.exs and edit the file to include HTTPoison as a dependency:
    defp deps do
    [{:httpoison, "~> 0.4"}]
end
  2. HTTPoison must be started with our system. Add this to the started applications list by including it inside the application function:
    def application do
    [applications: [:logger, :httpoison]]
end
  3. Save mix.exs and run mix deps.get to fetch the declared dependencies, as shown in this screenshot:
    How to do it…
  4. Compile the dependencies by executing mix deps.compile, as shown in the following screenshot:
    How to do it…

    Note

    Sometimes, some of the dependencies are Erlang projects, so you may get a prompt asking you to install rebar (rebar is a tool similar to Mix used in Erlang projects). Once you accept to download it, it will be available in your system and you won't have to worry about it anymore.

  5. Start your application with iex –S mix.
  6. Inside the IEx session, check whether HTTPoison is running:
    iex(1)> :application.which_applications
[{:manage_deps, 'manage_deps', '0.0.1'},
 {:httpoison, '  Yet Another HTTP client for Elixir powered by hackney\n',
  '0.4.2'}, {:hackney, 'simple HTTP client', '0.13.1'}(…)]
  7. Get Google's main page using HTTPoison:
    iex(5)> HTTPoison.get("http://www.google.com")
%HTTPoison.Response{body: "<HTML><HEAD><meta http-equiv=\"content-type\" content=\"text/html;charset=utf-8\">\n<TITLE>302 Moved</TITLE></HEAD><BODY>\n<H1>302 Moved</H1>\nThe document has moved\n<A HREF=\"http://www.google.pt/?gfe_rd=cr&amp;ei=WFAOVLvQFJSs8wfehYJg\">here</A>.\r\n</BODY></HTML>\r\n",
 headers: %{"Alternate-Protocol" => "80:quic", "Cache-Control" => "private",
   "Content-Length" => "256", "Content-Type" => "text/html; charset=UTF-8",
   "Date" => "Tue, 09 Sep 2014 00:56:56 GMT",
   "Location" => "http://www.google.pt/?gfe_rd=cr&ei=WFAOVLvQFJSs8wfehYJg",
   "Server" => "GFE/2.0"}, status_code: 302}

How it works…

Dependencies are preferably added using hex.pm (https://hex.pm/).

Tip

If an application doesn't yet exist in Hex, it is also possible to use a GitHub repository as a source.

To fetch a dependency from GitHub, instead of declaring the dependency with the {:httpoison, "~> 0.4"} format, the following format is used:

{:httpoison, github: " edgurgel/httpoison "}

The local filesystem may also be configured as a source for dependencies, as follows:

 {:httpotion, path: "path/to/httpotion"}

Once the dependencies are declared inside the mix.exs file, there are Mix tasks to get, compile, and clean them. The dependencies are then fetched, and if these dependencies have more dependencies on themselves, Mix is smart enough to fetch them.

When compiling dependencies, Mix is also capable of figuring out whether any dependent application has its own dependencies and whether they need to be compiled.

Starting IEx with the –S Mix loads the Mix environment inside IEx, and the application becomes accessible.

As shown in the Inspecting your system recipe, it is possible to get a list of running applications and check whether our dependency (and its own dependencies) are running. In the particular case of HTTPoison, automatic start is ensured by adding the atom representing the application name to the list under applications ([applications: [:logger, :httpoison]]).

See also

End of Section 10
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