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Elixir Cookbook

By : Paulo Pereira

4.5 (2)

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.

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. Command Line

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. 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. 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. 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. 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. 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. 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. Interactions

8. Interactions

Introduction

Using Redis and Postgres

Using OS commands from within Elixir

Getting Twitter data

A. Installation and Further Reading

A. Installation and Further Reading

Installing Elixir

Installing PostgreSQL

Installing Redis

Some useful links

Index

Index

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Inspecting your system in IEx

Sometimes, we need to take a look at what is going on in a running VM. It is useful to see which applications are open and any information about memory usage.

We will use some Erlang modules to inspect a VM instance.

Getting ready

Start a new IEx session.

How to do it…

We will follow these steps to get information on our running system:

To get the currently running applications, type this:

iex(1)> :application.which_applications
[
  {:logger, 'logger', '0.15.1'},
  {:iex, 'iex', '0.15.1'},
  {:elixir, 'elixir', '0.15.1'}, 
  {:syntax_tools, 'Syntax tools', '1.6.15'},
  {:compiler, 'ERTS  CXC 138 10', '5.0.1'}, 
  {:crypto, 'CRYPTO', '3.4'},
  {:stdlib, 'ERTS  CXC 138 10', '2.1'}, 
  {:kernel, 'ERTS  CXC 138 10', '3.0.1'}
]

The list that is returned contains three-element tuples. The first element is an atom identifying the application, the second element is the application description, and the third is the application version.

We get information on the memory usage by running the following commands:

iex(2)> :erlang.memory
[total: 15474240, processes: 4958016, processes_used: 4957056, system: 10516224,
 atom: 256313, atom_used: 234423, binary: 15352, code: 6071692, ets: 399560]

It is also possible to get memory usage for atoms, ets tables, binaries, and so on:
```
iex(3)> :erlang.memory(:atom)
256313
```

How it works…

As we saw in the previous recipe, Using Erlang from Elixir, it is possible to seamlessly call Erlang code from Elixir. Even though there is no specific Elixir code to perform these inspections, it is easy to get these abilities via Erlang libraries.

See also

When a GUI environment is available, there's a tool called Observer that helps to get information on an Erlang VM. Take a look at the next recipe, Inspecting your system with Observer.

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