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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

Creating custom Mix tasks

Sometimes, the existing Mix tasks just aren't enough. Fortunately, Mix allows the creation of customized tasks that integrate as if they were shipped with Mix itself. In this recipe, we will create a custom Mix task that will print the Erlang VM memory status.

How to do it…

The steps required to create a custom task are as follows:

  1. Create a new file, meminfo.ex, that defines the Meminfo module inside Mix.Tasks:
    defmodule Mix.Tasks.Meminfo do
  use Mix.Task
end
  2. Add the new task description to be displayed when mix help is invoked:
    @shortdoc "Get Erlang VM memory usage information"
  3. Add the new task module documentation:
    @moduledoc """
  A mix custom task that outputs some information regarding 
  the Erlang VM memory usage
  """
  4. Create a run/1 function:
    def run(_) do
  meminfo = :erlang.memory
  IO.puts """
  Total            #{meminfo[:total]}
  Processes        #{meminfo[:processes]}
  Processes (used) #{meminfo[:processes_used]}
  System           #{meminfo[:system]}
  Atom             #{meminfo[:atom]}
  Atom (used)      #{meminfo[:atom_used]}
  Binary           #{meminfo[:binary]}
  Code             #{meminfo[:code]}
  ETS              #{meminfo[:ets]}
  """
end
  5. Compile the code using the Elixir compiler, elixirc:
    elixirc meminfo.ex

    No message should appear but a file named Elixir.Mix.Tasks.Meminfo.beam is created.

  6. Run mix help to see the new task listed and its short description:
    > mix help
mix               # Run the default task (current: mix run)
mix archive       # List all archives
(…)
mix meminfo     # Get Erlang VM memory usage information
mix new           # Create a new Elixir project
mix run           # Run the given file or expression
mix test          # Run a project's tests
iex -S mix        # Start IEx and run the default task
  7. Execute the custom task:
    > mix meminfo
Total            17692216
Processes        4778984
Processes (used) 4777656
System           12913232
Atom             339441
Atom (used)      321302
Binary           14152
Code             8136817
ETS              452832

How it works…

Mix tasks are just modules that are declared as Mix.Tasks.<MODULENAME> with a run function defined.

In meminfo.ex, we use the Mix.Task module by declaring use Mix.Task. The use directive allows us to use a given module in the current context.

The @shortdoc attribute allows us to define a short description to display when some help on Mix or the mix.task is displayed.

The run/1 function is the place where all of the task's work is done. In this particular case, we use an Erlang function to return a keyword list with several entries, and print them for the user in a formatted way.

End of Chapter 1
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