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https://github.com/dwyl/learn-elixir
:droplet: Learn the Elixir programming language to build functional, fast, scalable and maintainable web applications!
https://github.com/dwyl/learn-elixir
Last synced: about 1 month ago
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:droplet: Learn the Elixir programming language to build functional, fast, scalable and maintainable web applications!
- Host: GitHub
- URL: https://github.com/dwyl/learn-elixir
- Owner: dwyl
- Created: 2016-12-01T06:33:44.000Z (almost 8 years ago)
- Default Branch: main
- Last Pushed: 2024-09-14T15:19:23.000Z (2 months ago)
- Last Synced: 2024-10-01T11:22:06.135Z (about 1 month ago)
- Language: Elixir
- Homepage:
- Size: 4.97 MB
- Stars: 1,612
- Watchers: 179
- Forks: 107
- Open Issues: 123
-
Metadata Files:
- Readme: README.md
Awesome Lists containing this project
README
# Learn 
- [Learn ](#learn-)
- [_Why_?](#why)
- [Key Advantages](#key-advantages)
- [_What_?](#what)
- [Video Introductions](#video-introductions)
- [_How_?](#how)
- [Installation:](#installation)
- [Mac:](#mac)
- [Ubuntu:](#ubuntu)
- [Windows:](#windows)
- [Livebook:](#livebook)
- [Learn Elixir](#learn-elixir)
- [Commands](#commands)
- [Basic Types](#basic-types)
- [Numbers](#numbers)
- [Booleans](#booleans)
- [Truthiness: truthy and falsy values](#truthiness-truthy-and-falsy-values)
- [Atoms](#atoms)
- [Strings](#strings)
- [Lists](#lists)
- [Tuples](#tuples)
- [Lists or Tuples?](#lists-or-tuples)
- [Functions and Modules](#functions-and-modules)
- [Anonymous functions](#anonymous-functions)
- [Modules](#modules)
- [Create Your First `Elixir` Project](#create-your-first-elixir-project)
- [Initialise](#initialise)
- [Edit `animals.ex`](#edit-animalsex)
- [Run the Code](#run-the-code)
- [Define Functions](#define-functions)
- [Extend Functions](#extend-functions)
- [Add More Functions!](#add-more-functions)
- [Pattern Matching _Example_](#pattern-matching-example)
- [Save Data to File](#save-data-to-file)
- [Retrieve Data from File](#retrieve-data-from-file)
- [Pipe Operator](#pipe-operator)
- [Documentation](#documentation)
- [Testing](#testing)
- [Formatting](#formatting)
- [Publishing](#publishing)
- [Congratulations!](#congratulations)
- [Want _More_?](#want-more)
- [Data Structures](#data-structures)
- [Maps](#maps)
- [Updating a value inside a map](#updating-a-value-inside-a-map)
- [Processes](#processes)
- [Spawning a process](#spawning-a-process)
- [Sending messages between processes](#sending-messages-between-processes)
- [Concurrency](#concurrency)
- [tl;dr](#tldr)
- [Further resources:](#further-resources)
## _Why_?
### Key Advantages
- **Scalability**
- **Speed**
- **Compiled** and run on the **Erlang VM** ("BEAM"). [(Renowned for efficiency)](http://stackoverflow.com/questions/16779162/what-kind-of-virtual-machine-is-beam-the-erlang-vm)
- Much better ["garbage collection"](http://searchstorage.techtarget.com/definition/garbage-collection) than virtually any other VM
- Many tiny processes (as opposed to "threads"
which are more difficult to manage)
- **Functional** language with [dynamic](https://www.sitepoint.com/typing-versus-dynamic-typing/) typing
- [Immutable data](https://benmccormick.org/2016/06/04/what-are-mutable-and-immutable-data-structures-2/) so ["state"](http://softwareengineering.stackexchange.com/questions/235558/what-is-state-mutable-state-and-immutable-state) is always **predictable**!
- **High reliability, availability and fault tolerance** (_because of Erlang_)
means apps built with **`Elixir`** are run in production for **years**
without any "_downtime_"!
- Real-time web apps are "_easy_"
(_or at least easier than many other languages!_) as **WebSockets & streaming** are baked-in
Things _will_ go wrong with
code, and **`Elixir`** provides supervisors which describe how to restart parts of
your system when things don't go as planned.
## _What_?
[_"Elixir is a dynamic, functional language designed for building scalable and
maintainable applications."_](http://elixir-lang.org/)
### Video Introductions
If you have the time, these videos give a nice contextual introduction into what **`Elixir`** is, what it's used for and how it works:
- Code School's [Try Elixir](https://www.codeschool.com/courses/try-elixir), 3 videos (25mins :movie_camera: plus exercises, totalling 90mins). The 'Try' course is free (there is an extended paid for course).
- Pete Broderick's [Intro to Elixir](https://youtu.be/lly-1UYmnFI) (41 mins :movie_camera:)
- Jessica Kerr's [Elixir Should Take Over the World](https://youtu.be/X25xOhntr6s) (58 mins :movie_camera:)
Not a video learner? Looking for a specific learning? https://elixirschool.com/ is an excellent, free, open-source resource that explains all things **`Elixir`** :book: :heart:.
## _How_?
Before you learn **`Elixir`** as a language you will need to have it installed on your machine.
To do so you can go to
http://elixir-lang.org/install.html or follow our guide here:
### Installation:
#### Mac:
Using the [Homebrew](https://brew.sh/) package manager:
`brew install elixir`
> If you have any trouble with `ssl` when running an `Elixir` App on your `Mac`,
> see:
> [`/install-mac.md`](https://github.com/dwyl/learn-elixir/blob/main/install-mac.md)
#### Ubuntu:
- **Add the Erlang Solutions repo**:
```
wget https://packages.erlang-solutions.com/erlang-solutions_2.0_all.deb && sudo dpkg -i erlang-solutions_2.0_all.deb
```
- **Run**: `sudo apt-get update`
- **Install the Erlang/OTP platform and all of its applications**:
`sudo apt-get install esl-erlang`
- **Install Elixir**: `sudo apt-get install elixir`
#### Windows:
- **Web installer**
- [Download the installer](https://repo.hex.pm/elixir-websetup.exe)
- Click next, next, ..., finish
- **Chocolatey** (_Package Manager_)
```
choco install elixir
```
#### Livebook:
- Easy peasy if you have `Elixir` installed. Just click below
👉 [
](https://livebook.dev/)
Once `Livebook` installed on your machine, just click on the button below (or fork and run it):
[](https://livebook.dev/run?url=https%3A%2F%2Fgithub.com%2Fdwyl%2Flearn-elixir%2Fblob%2Fmain%2Flearn-elixir-on-livebook.livemd)
- Alternatively, you can run a `Docker` image, no need to install `Elixir` or `Livebook`. Launch `Docker` and run the `Livebook` image:
```
docker run -p 8080:8080 -p 8081:8081 --pull always -e LIVEBOOK_PASSWORD="securesecret" livebook/livebook
```
and in another terminal you launch the browser (you will need to authneticate with "securesecret") with the command:
```
open http://localhost:8080/import?url=https://github.com/dwyl/learn-elixir/blob/main/learn-elixir-on-livebook.livemd
```
- Finally, if you don't have `Docker` nor `Elixir` and `Livebook` installed, you can run a remote version in the cloud. Follow this!
You (**right**-)click on the grey button **"Run in Livebook"** below.
:heavy_exclamation_mark: You **right-click"** to keep this reminder page open 😉 because you will need to remember to do 2 things:
1. firstly, look at the bottom for the link "see source" as showed below, 🤔, and click.
2. and finally, select the file [dwyl-learn-elixir.livemd]. It should be printed in green, and "join session". 🤗
Happy learning! 🥳
This links to the remote Livebook: 👉
[](https://livebook.dev/run?url=https%3A%2F%2Fdwyl-learn-elixir.fly.dev%2F)
## Learn Elixir
## Commands
- After installing **`Elixir`** you can open the interactive shell by typing `iex`.
This allows you to type in any **`Elixir`** expression and see the result in the terminal.
- Type in `h` followed by the `function` name at any time to see documentation information about any given built-in function and how to use it. E.g If you type `h round` into the (iex) terminal you should see
something like this:
- Typing `i` followed by the value name will give you information about a value in your code:
## Basic Types
This section brings together the key information from Elixir's
[Getting Started](http://elixir-lang.org/getting-started/basic-types.html)
documentation and multiple other sources. It will take you through some examples to practice using and familiarise yourself with Elixir's 7 basic types.
Elixir's 7 basic types:
- `integers`
- `floats`
- `booleans`
- `atoms`
- `strings`
- `lists`
- `tuples`
### Numbers
Type `1 + 2` into the terminal (after opening `iex`):
```elixir
iex> 1 + 2
3
```
More examples:
```elixir
iex> 5 * 5
25
iex> 10 / 2
5.0
# When using the `/` with two integers this gives a `float` (5.0).
# If you want to do integer division or get the division remainder
# you can use the `div` or `rem` functions
iex> div(10, 2)
5
iex> div 10, 2
5
iex> rem 10, 3
1
```
### Booleans
Elixir supports `true` and `false` as booleans.
```elixir
iex> true
true
iex> false
false
iex> is_boolean(true)
true
iex> is_boolean(1)
false
```
### Truthiness: truthy and falsy values
Besides the booleans `true` and `false` **`Elixir`** also has the
concept of a "truthy" or "falsy" value.
- a value is truthy when it is neither `false` nor `nil`
- a value is falsy when it is `false` or `nil`
Elixir has functions, like `and/2`, that _only_ work with
booleans, but also functions that work with these
truthy/falsy values, like `&&/2` and `!/1`.
The syntax `/` is the convention
used in Elixir to identify a function named
`` that takes `` parameters.
The value `` is also referred to as the function
[arity](https://en.wikipedia.org/wiki/Arity).
In Elixir each function is identified univocally both by
its name and its arity. More information can be found [here](https://culttt.com/2016/05/02/understanding-function-arity-elixir/).
We can check the truthiness of a value by using the `!/1`
function twice.
Truthy values:
```elixir
iex> !!true
true
iex> !!5
true
iex> !![1,2]
true
iex> !!"foo"
true
```
Falsy values (of which there are exactly two):
```elixir
iex> !!false
false
iex> !!nil
false
```
### Atoms
Atoms are constants where their name is their own value
(some other languages call these Symbols).
```elixir
iex> :hello
:hello
iex> :hello == :world
false
```
`true` and `false` are actually atoms in Elixir
Names of _modules_ in **`Elixir`** are also atoms. `MyApp.MyModule`
is a valid atom, even if no such module has been declared yet.
```elixir
iex> is_atom(MyApp.MyModule)
true
```
Atoms are also used to reference modules from Erlang libraries,
including built-in ones.
```elixir
iex> :crypto.strong_rand_bytes 3
<<23, 104, 108>>
```
One popular use of atoms in **`Elixir`** is to use them as messages
for [pattern matching](https://en.wikipedia.org/wiki/Pattern_matching).
Let's say you have a function which processes an `http` request.
The outcome of this process is either going to be a success or an error.
You could therefore use atoms to indicate whether
or not this process is successful.
```elixir
def process(file) do
lines = file |> split_lines
case lines do
nil ->
{:error, "failed to process file"}
lines ->
{:ok, lines}
end
end
```
Here we are saying that the method,
`process/1` will return a [tuple](#) response.
If the result of our process is successful, it will return `{:ok, lines}`,
however if it fails (e.g. returns nil) then it will return an error.
This will allows us to _pattern_ match on this result.
```elixir
{:ok, lines} = process('text.txt')
```
Thus, we can be sure that we will always have the lines returned to us
and never a _nil_ value (because it will throw an error).
This becomes extremely useful when piping multiple methods together.
### Strings
Strings are surrounded by double quotes.
```elixir
iex> "Hello World"
"Hello world"
# You can print a string using the `IO` module
iex> IO.puts "Hello world"
"Hello world"
:ok
```
### Lists
Elixir uses square brackets to make a list.
```elixir
iex> myList = [1,2,3]
iex> myList
[1,2,3]
iex> length(myList)
3
# concatenating lists together
iex> [1, 2, 3] ++ [4, 5, 6]
[1, 2, 3, 4, 5, 6]
# removing items from a list
iex> [1, true, 2, false, 3, true] -- [true, false]
[1, 2, 3, true]
```
Lists are [enumerable](https://github.com/dwyl/learn-elixir/issues/39) and can use the [Enum](https://hexdocs.pm/elixir/Enum.html)
module to perform iterative functions such as mapping.
### Tuples
Elixir uses curly brackets to make a tuple.
Tuples are similar to lists but are
[not suited to data sets that need to be updated or added to regularly](#lists-or-tuples).
```elixir
iex> tuple = {:ok, "hello"}
{:ok, "hello"}
# get element at index 1
iex> elem(tuple, 1)
"hello"
# get the size of the tuple
iex> tuple_size(tuple)
2
```
Tuples are [not enumerable](https://github.com/dwyl/learn-elixir/issues/39) and there are far fewer functions available
in the [Tuple](http://elixir-lang.org/docs/v1.0/elixir/Tuple.html) module. You can reference tuple values by index but [you cannot iterate over them](https://github.com/dwyl/learn-elixir/issues/39).
If you must treat your tuple as a list,
then convert it using `Tuple.to_list(your_tuple)`
### Lists or Tuples?
If you need to iterate over the values use a list.
When dealing with **large** lists or tuples:
- `Updating` a `list` (adding or removing elements) is **fast**
- `Updating` a `tuple` is **slow**
- `Reading` a `list` (getting its length or selecting an element) is **slow**
- `Reading` a `tuple` is **fast**
> source: http://stackoverflow.com/questions/31192923/lists-vs-tuples-what-to-use-and-when
## Functions and Modules
### Anonymous functions
Anonymous functions start with `fn` and end with `end`.
```elixir
iex> add = fn a, b -> a + b end
iex> add.(1, 2)
3
```
Note a dot `.` between the variable `add` and parenthesis is required
to invoke an anonymous function.
In Elixir, functions are `first class citizens` meaning that they can
be passed as arguments to other functions the same way integers and strings can.
```elixir
iex> is_function(add)
true
```
This uses the inbuilt function `is_function` which checks to see if
the parameter passed is a function and returns a bool.
Anonymous functions are [closures](https://developer.mozilla.org/en/docs/Web/JavaScript/Closures) (_named_ functions are not)
and as such they can access variables
that are in scope when the function is defined.
You can define a new anonymous function that uses the `add`
anonymous function we have previously defined:
```elixir
iex> double = fn a -> add.(a, a) end
iex> double.(5)
10
```
These functions can be useful but will no longer be available to you.
If you want to make something more permanent then you can create a `module`.
### Modules
With modules you're able to group several functions together.
Most of the time it is convenient to write modules into files
so they can be compiled and reused.
Get started by creating a file named `math.ex`,
open it in your text editor and add the following code
```elixir
defmodule Math do
def sum(a, b) do
a + b
end
end
```
In order to create your own modules in Elixir, use the `defmodule` [macro](https://www.google.co.uk/webhp?sourceid=chrome-instant&ion=1&espv=2&ie=UTF-8#q=what+is+a+macro&*),
then use the `def` macro to define functions in that module.
So in this case the module is `Math` and the function is `sum`.
Once this is saved the file can be compiled by typing `elixirc`
into the terminal followed by the file name.
```
$ elixirc math.ex
```
This will generate a file named `Elixir.Math.beam` containing the bytecode
for the defined module. If we start `iex` again, our module definition
will be available (provided that `iex` is started
in the same directory the bytecode file is in):
```elixir
iex> Math.sum(1, 2)
3
```
## Create Your First `Elixir` Project
To get started
with your first **`Elixir`** project
you need to make use of the
[**`Mix`**](https://hexdocs.pm/mix/Mix.html)
build tool that comes with **`Elixir`**.
Mix allows you to do a number of things including:
- Create projects
- Compile projects
- Run tasks
- Testing
- Generate documentation
- Manage dependencies
To generate a new project follow these steps:
### Initialise
Initialise a project by typing the following command in your terminal,
replacing [project_name] with the name of your project:
```sh
mix new [project_name]
```
e.g:
```sh
mix new animals
```
We have chosen to call our project 'animals'
This will create a new folder
with the given name of your project
and should also print something
that looks like this to the command line:
```bash
* creating README.md
* creating .formatter.exs
* creating .gitignore
* creating mix.exs
* creating lib
* creating lib/animals.ex
* creating test
* creating test/test_helper.exs
* creating test/animals_test.exs
Your Mix project was created successfully.
You can use "mix" to compile it, test it, and more:
cd animals
mix test
Run "mix help" for more commands.
```
Navigate to your newly created directory:
```bash
> cd animals
```
Open the directory in your text editor. You will be able to see that **`Elixir`** has
generated a few files for us that are specific to our project:
- `lib/animals.ex`
- `test/animals_test.ex`
### Edit `animals.ex`
Open up the `animals.ex` file
in the lib directory.
You should already see some
`hello-world` boilerplate like this:
```elixir
defmodule Animals do
@moduledoc """
Documentation for Animals.
"""
@doc """
Hello world.
## Examples
iex> Animals.hello()
:world
"""
def hello do
:world
end
end
```
**`Elixir`** has created a module
with the name of your project
along with a function
that prints out a `:world` atom when called.
It's also added boilerplate for
module and function documentation - the first part of the file.
(_we will go into more detail about documentation later_)
### Run the Code
Let's test out the boilerplate code.
In your project directory type the following command:
```sh
> iex -S mix
```
What this means is:
"Start the **`Elixir` REPL**
and compile with the context of my current project".
This allows you to access modules and
functions created within the file tree.
Call the `hello-world` function given to us by **`Elixir`**.
It should print out the
`:world` atom to the command line:
```bash
> Animals.hello
# :world
```
### Define Functions
Let's start to create our own methods in the `Animals` module.
Replace the `hello-world` function with the following:
```elixir
@doc """
create_zoo returns a list of zoo animals
## Examples
iex> Animals.create_zoo
["lion", "tiger", "gorilla", "elephant", "monkey", "giraffe"]
"""
def create_zoo do
["lion", "tiger", "gorilla", "elephant", "monkey", "giraffe"]
end
```
To run our new code we will first have to recompile our `iex`.
This can be done by typing:
```sh
> recompile()
```
Now we will have access to the `create_zoo` method. Try it out in the command line:
```sh
> Animals.create_zoo
# ["lion", "tiger", "gorilla", "elephant", "monkey", "giraffe"]
```
### Extend Functions
Let's _extend_ the `Animals` module.
Imaging you're visiting the zoo
but you can't decide which order to view the animals.
We can create a `randomise` function
before the final `end` that takes a list of animals
and returns a new list with a random order:
```elixir
@doc """
randomise takes a list of zoo animals and returns a new randomised list with
the same elements as the first.
## Examples
iex> zoo = Animals.create_zoo
iex> Animals.randomise(zoo)
["monkey", "tiger", "elephant", "gorilla", "giraffe", "lion"]
"""
def randomise(zoo) do
Enum.shuffle(zoo)
end
```
> **Note**: we are making use
> of a pre-built module called `Enum`
> which has a list of functions
> that you can use on enumerables such as lists.
> Documentation available at:
> [hexdocs.pm/elixir/Enum.html](https://hexdocs.pm/elixir/Enum.html)
### Add More Functions!
Let's add another function
to the `Animals` module.
We want to find out
if our zoo contains an animal:
```elixir
@doc """
contains? takes a list of zoo animals and a single animal and returns a boolean
as to whether or not the list contains the given animal.
## Examples
iex> zoo = Animals.create_zoo
iex> Animals.contains?(zoo, "gorilla")
true
"""
def contains?(zoo, animal) do
Enum.member?(zoo, animal)
end
```
**NOTE:** It's convention when writing a function that returns a boolean to add a question
mark after the name of the method.
### Pattern Matching _Example_
Create a function
that takes a list of animals
and the number of animals
that you'd like to see
and returns a list of animals:
```elixir
@doc """
see_animals takes a list of zoo animals and the number of animals that
you want to see and then returns a list
## Examples
iex> zoo = Animals.create_zoo
iex> Animals.see_animals(zoo, 2)
["monkey", "giraffe"]
"""
def see_animals(zoo, count) do
# Enum.split returns a tuple so we have to pattern match on the result
# to get the value we want out
{_seen, to_see} = Enum.split(zoo, -count)
to_see
end
```
### Save Data to File
Write a function
that will
save our list of animals to a file:
```elixir
@doc """
save takes a list of zoo animals and a filename and saves the list to that file
## Examples
iex> zoo = Animals.create_zoo
iex> Animals.save(zoo, "my_animals")
:ok
"""
def save(zoo, filename) do
# erlang is converting the zoo list to something that can be written to the
# file system
binary = :erlang.term_to_binary(zoo)
File.write(filename, binary)
end
```
In your command line,
run the following after recompiling:
```sh
> zoo = Animals.create_zoo
> Animals.save(zoo, "my_animals")
```
This will create a new file
in your file tree with the name of the file that
you specified in the function.
It will contain some odd characters:
�l\\mlionmtigermgorillamelephantmmonkeymgiraffej
### Retrieve Data from File
Write a function
that will fetch data from the file:
```elixir
@doc """
load takes filename and returns a list of animals if the file exists
## Examples
iex> Animals.load("my_animals")
["lion", "tiger", "gorilla", "elephant", "monkey", "giraffe"]
iex> Animals.load("aglkjhdfg")
"File does not exist"
"""
def load(filename) do
# here we are running a case expression on the result of File.read(filename)
# if we receive an :ok then we want to return the list
# if we receive an error then we want to give the user an error-friendly message
case File.read(filename) do
{:ok, binary} -> :erlang.binary_to_term(binary)
{:error, _reason} -> "File does not exist"
end
end
```
The
[`case` expression](https://elixir-lang.org/getting-started/case-cond-and-if.html)
allows us to pattern match
against various options and react accordingly.
#### Pipe Operator
What if we wanted to call some of our functions in succession to another? Let's create a function that creates a zoo, randomises it and then returns a selected number of animals to go and see:
```elixir
@doc """
selection takes a number, creates a zoo, randomises it and then returns a list
of animals of length selected
## Examples
iex> Animals.selection(2)
["gorilla", "giraffe"]
"""
def selection(number_of_animals) do
# We are using the pipe operator here. It takes the value returned from
# the expression and passes it down as the first argument in the expression
# below. see_animals takes two arguments but only one needs to be specified
# as the first is provided by the pipe operator
Animals.create_zoo()
|> Animals.randomise()
|> Animals.see_animals(number_of_animals)
end
```
Now that we have the functionality for our module,
let's take a look at the documentation
that we have written
and how we can maximise its use.
## Documentation
When we created a new project with mix, it created a file for us called `mix.exs`
which is referred to as the 'MixFile'. This file holds information about our
project and its dependencies.
At the bottom of the file it gives us a function called `deps` which manages all
of the dependencies in our project. To install a third party package we need to
manually write it in the deps function (_accepts a tuple of the package name and
the version_) and then install it in the command line. Let's install `ex_doc` as
an example:
Add the following to the deps function in your `mix.exs` file:
```elixir
defp deps do
[
{:ex_doc, "~> 0.21"}
]
end
```
Then in the command line quit your `iex` shell and enter the following to install
the `ex_docs` dependency:
```sh
> mix deps.get
```
You might receive an error saying:
```sh
Could not find Hex, which is needed to build dependency :ex_doc
Shall I install Hex? (if running non-interactively,
use: "mix local.hex --force") [Yn]
```
If you do then just enter `y`
and then press enter.
This will install the
dependencies that you need.
Once `ex_docs` has been installed,
run the following command to generate
documentation (_make sure you're not in `iex`_):
```sh
> mix docs
```
This will generate documentation
that can be viewed
if you copy the file path
of the `index.html` file
within the newly created `doc` folder
and then paste it in your browser.
If you have added documentation
to your module and functions
as per the examples above,
you should see something like the following:
It looks exactly like the format
of the official **`Elixir`** docs
because they used the same tool to create theirs.
Here is what the method documentation
should look like if you click on `Animals`:
This is an incredibly powerful tool
that comes 'baked in' with elixir.
It means that other developers
who are joining the project
can be brought up to speed incredibly quickly!
## Testing
When you generate a project with **`Elixir`** it automatically gives you a number of
files and directories. One of these directories is called `test` and it holds two
files that should have names like:
- `[project_name]_test.exs`
- `test_helper.exs`
Our first file was called `animals_test.exs` and it contained some boilerplate that
looks like:
```elixir
defmodule AnimalsTest do
use ExUnit.Case
doctest Animals
test "greets the world" do
assert Animals.hello() == :world
end
end
```
**NOTE:** It automatically includes a line called `doctest Animals`. What this means
is that it can run tests from the examples in the documentation that you write for
your functions
To run the tests enter the following in your terminal:
`mix test`
It should print out whether the tests pass or fail.
Let's add some tests of our own. Firstly let's write a test for the `Animals.randomise`
function. The reason why we wouldn't want to write a doctest for this is because
the output value changes everytime you call it. Here's how we would write a test
for that type of function:
In the `animals_test.exs` file, remove the boilerplate "greets the world" test and then
add this to test that the order of the animals in `zoo` changes (is randomised):
```elixir
test "randomise" do
zoo = Animals.create_zoo
assert zoo != Animals.randomise(zoo)
end
```
**NOTE: You do not need to install and require any external testing frameworks**.
It all comes with the **`Elixir`** package. Simply write `test` followed by a string
representing what you are trying to test and then write your assertion.
The test above isn't completely air-tight. **`Elixir`** provides you with assertions that
can help deal with things like this. The test could be re-written like so:
```elixir
test "randomise" do
zoo = Animals.create_zoo
refute zoo == Animals.randomise(zoo)
end
```
This is basically saying "prove to be false that zoo is equal to Animals.randomise(zoo)"
If you want to learn about code coverage then check out the following
tutorial,
https://github.com/dwyl/learn-elixir/tree/master/codecov_example
## Formatting
In **`Elixir`** version 1.6 the `mix format` task was introduced.
see: https://github.com/elixir-lang/elixir/issues/6643
`mix format` is a _built-in_ way to format your **`Elixir`** code
according to the community-agreed consistent style.
This means _all_ code will look consistent across projects
(_personal, "work" & hex.pm packages_)
which makes learning faster and maintainability easier!
At present, using the formatter is _optional_,
however _most_ **`Elixir`** projects have adopted it.
To _use_ the mix task in your project,
you can either check files _individually_, e.g:
```sh
mix format path/to/file.ex
```
Or you can define a _pattern_ for types of files
you want to check the format of:
```sh
mix format "lib/**/*.{ex,exs}"
```
will check all the `.ex` and `.exs` files in the `lib/` directory.
Having to type this pattern each time
you want to check the files is _tedious_.
Thankfully, **`Elixir`** has you covered.
In the root of your **`Elixir`** project, you will find a `.formatter.exs`
config file with the following code:
```elixir
# Used by "mix format"
[
inputs: ["{mix,.formatter}.exs", "{config,lib,test}/**/*.{ex,exs}"]
]
```
This means that if you run `mix format` it will check the `mix.exs` file
and _all_ `.ex` and `.exs` files in the `config`, `lib/` and `test` directories.
This is the most common pattern for running mix format.
Unless you have a _reason_ to "deviate" from it, it's a good practice to keep it as it is.
Simply run:
```sh
mix format
```
And your code will now follow Elixir's formatting guidelines.
We recommend installing a plugin in your Text Editor to auto-format:
- **Atom** Text Editor Auto-formatter:
https://atom.io/packages/atom-elixir-formatter
- Vim **`Elixir`** Formatter: https://github.com/mhinz/vim-mix-format
- VSCode:
https://marketplace.visualstudio.com/items?itemName=sammkj.vscode-elixir-formatter
- Read the `mix/tasks/format.ex` source to _understand_ how it works:
https://github.com/elixir-lang/elixir/blob/master/lib/mix/lib/mix/tasks/format.ex
- https://hashrocket.com/blog/posts/format-your-elixir-code-now
- https://devonestes.herokuapp.com/everything-you-need-to-know-about-elixirs-new-formatter
## Publishing
To publish your **`Elixir`** package to [Hex.pm](https://hex.pm/):
- Check the version in `mix.exs` is up to date and that it follows the
[semantic versioning format](https://semver.org/):
> MAJOR.MINOR.PATCH where
MAJOR version when you make incompatible API changes
MINOR version when you add functionality in a backwards-compatible manner
PATCH version when you make backwards-compatible bug fixes
- Check that the main properties of the project are defined in `mix.exs`
- name: The name of the package
- description: A short description of the package
- licenses: The names of the licenses of the package
- NB. dwyl's `cid` repo contains an [example of a more advanced
`mix.exs` file](https://github.com/dwyl/cid/blob/master/mix.exs) where
you can see this in action
- Create a [Hex.pm](https://hex.pm/) account
if you do not have one already.
- Make sure that [ex_doc](https://hex.pm/packages/ex_doc)
is added as a dependency in you project
```elixir
defp deps do
[
{:ex_doc, "~> 0.21", only: :dev}
]
end
```
When publishing a package, the documentation will be automatically generated.
So if the dependency `ex_doc` is not declared, the package won't be able to be published
- Run `mix hex.publish`
and if all the information are correct reply `Y`
If you have not logged into your Hex.pm account
in your command line before running the above command,
you will be met with the following...
```sh
No authenticated user found. Do you want to authenticate now? [Yn]
```
You will need to reply `Y`
and follow the on-screen instructions
to enter your Hex.pm username and password.
After you have been authenticated,
Hex will ask you for a local password that
applies only to the machine you are using for security purposes.
Create a password for this
and follow the onscreen instructions to enter it.
- Now that your package is published you can create a new git tag with the name of the version:
- `git tag -a 0.1.0 -m "0.1.0 release"`
- `git push --tags`
### Congratulations!
That's it, you've generated, formatted
and published your first **`Elixir`** project :tada:
### Want _More_?
If you want a more detailed example
of publishing a real-world package
and re-using it in a real-world project,
see:
[**`code-reuse-hexpm.md`**](https://github.com/dwyl/learn-elixir/blob/main/code-reuse-hexpm.md)
## Data Structures
### Maps
Maps are very similar to `Object` literals in `JavaScript`.
They have almost the same
syntax except for a `%` symbol.
They look like this:
```elixir
animal = %{
name: "Rex",
type: "dog",
legs: 4
}
```
Values can be accessed in a couple of ways.
The first is by dot notation just
like `JavaScript`:
```elixir
name = animal.name
# Rex
```
The second way values
can be accessed is by pattern matching.
Let's say we wanted
to assign values to variables
for each of the key-value pairs in the map.
We would write something that looks like this:
```elixir
iex> %{
name: name,
type: type,
legs: legs
} = animal
# we now have access to the values by typing the variable names
iex> name
# "Rex"
iex> type
# "dog"
iex> legs
# 4
```
#### Updating a value inside a map
Due to the immutability of **`Elixir`**,
you cannot update a map
using dot notation
for example:
```elixir
iex> animal = %{
name: "Rex",
type: "dog",
legs: 4
}
iex> animal.name = "Max" # this cannot be done!
```
In **`Elixir`** we can only create new data structures as opposed to manipulating existing
ones. So when we _update_ a map, we are creating a new map with our new values.
This can be done in a couple of ways:
- Function
- Syntax
1. Using a function
We can update a map using `Map.put(map, key, value)`.
This takes the map you want to update
followed by the key we want to reassign
and lastly the value that we want
to reassign to the key:
```elixir
iex> updatedAnimal = Map.put(animal, :name, "Max")
iex> updatedAnimal
# %{legs: 4, name: "Max", type: "dog"}
```
2. Using syntax
We can use a special syntax for updating a map in Elixir.
It looks like this:
```elixir
iex> %{animals | name: "Max"}
# %{legs: 4, name: "Max", type: "dog"}
```
> **NOTE:** Unlike the function method above,
> this syntax can only be used to UPDATE
> a current key-value pair inside the map,
> it cannot add a new key value pair.
## Processes
When looking into **`Elixir`** you may have heard about its
[processes](https://elixir-lang.org/getting-started/processes.html)
and its support for concurrency.
In fact we even mention processes
as one of the key advantages.
If you're anything like us,
you're probably wondering
what this actually means for you and your code.
This section aims to help you
understand what they are
and how they can help improve
your **`Elixir`** projects.
**`Elixir-lang`** describes processes as:
> In **`Elixir`**, all code runs inside processes.
> Processes are isolated from each other,
> run concurrent to one another
> and communicate via message passing.
> Processes are not only the basis
> for concurrency in **`Elixir`**,
> but they also provide the means
> for building distributed and fault-tolerant programs.
Now that we have a definition,
let's start by spawning our first process.
### Spawning a process
Create a file called `math.exs`
and insert the following code:
```elixir
defmodule Math do
def add(a, b) do
a + b
|> IO.inspect()
end
end
```
Now head over to your terminal
and enter the following, `iex math.exs`.
This will load your `Math` module
into your `iex` session.
Now in `iex` type:
```elixir
spawn(Math, :add, [1,2])
```
You will see something similar to:
```elixir
3
#PID<0.118.0>
```
This is your log
followed by a `process identifier`, PID for short.
A PID is a unique id for a process.
It could be unique among all processes in the world,
but here it's just unique for your application.
So what just happened here.
We called the
[`spawn/`3](https://hexdocs.pm/elixir/Kernel.html#spawn/3)
function
and passed it 3 arguments.
The module name,
the function name (as an atom),
and a list of the arguments
that we want to give to our function.
This one line of code spawned
a process for us 🎉 🥳
Normally we would not see the result
of the function (3 in this case).
The only reason we have
is because of the `IO.inspect` in the add function.
If we removed this the only log we would have is the PID itself.
This might make you wonder,
what good is spawning a process if I can't get
access to the data it returns.
This is where messages come in.
### Sending messages between processes
Let's start by exiting `iex`
and removing the the `IO.inspect` line
from our code.
Now that that is done
let's get our add function
to send its result in a message.
Update your file to the following:
```elixir
defmodule Math do
def add(a, b) do
receive do
senders_pid ->
send(senders_pid, a + b)
end
end
def double(n) do
spawn(Math, :add, [n,n])
|> send(self())
receive do
doubled ->
doubled
end
end
end
```
Let's go through all the new code.
We have added a new function called double. This function spawns the `Math.add/2`
function (as we did in the `iex` shell in the previous example). Remember the
spawn function returned a PID. We use this PID on the next line with
`|> send(self())`. [send/2](https://hexdocs.pm/elixir/Kernel.html#send/2) takes
two arguments, a destination and a message. For us the destination is the PID
created by the `spawn` function on the line above. The message is
[`self/0`](https://hexdocs.pm/elixir/Kernel.html#self/0)
which returns the PID
of the calling process (the PID of double).
We then call
[`receive/1`](https://hexdocs.pm/elixir/Kernel.SpecialForms.html#receive/1)
which checks if there is a message matching the clauses in the current process.
It works very similarly to a `case` statement.
Our `message` is simple and just
returns whatever the message was.
We have also updated our `add/2` function
so that it also contains a `receive` and a `send`.
This `receive`, receives the PID of the sender.
Once it has that message
it calls the send function
to send a message back to the sender.
The message it sends is `a+b`.
This will trigger the receive block in our double function. As mentioned
above, it simply returns the message it receives which is the answer from add.
Let's test this code in `iex`. Change to your terminal and type
`iex math.exs` again. In `iex` type `Math.double(5)`.
You should see
```elixir
10
```
VERY COOL.
We just spawned a process
which did a task for us
and returned the data.
### Concurrency
Now that we can create processes that can send messages to each other, let's see
if we can use them for something a little more intensive than doubling an
integer.
In this example we will aim to see exactly how concurrency can be used to
speed up a function (and in turn, hopefully a project).
We are going to do this by solving factorials using two different approaches.
One will solve them on a single process and the other will solve them using
multiple processes.
(A factorial is the product of an integer and all the integers below it;
e.g. `factorial(4) (4!)` is equal to `1 * 2 * 3 * 4` or `24`.)
Create a new file called `factorial.exs` with the following code:
```elixir
defmodule Factorial do
def spawn(n) do
1..n
|> Enum.chunk_every(4)
|> Enum.map(fn(list) ->
spawn(Factorial, :_spawn_function, [list])
|> send(self())
receive do
n -> n
end
end)
|> calc_product()
end
def _spawn_function(list) do
receive do
sender ->
product = calc_product(list)
send(sender, product)
end
end
# used on the single process
def calc_product(n) when is_integer(n) do
Enum.reduce(1..n, 1, &(&1 * &2))
end
# used with multiple processes
def calc_product(list) do
Enum.reduce(list, 1, &(&1 * &2))
end
end
```
The `&` symbol is called the
[capture operator](https://hexdocs.pm/elixir/Function.html#module-the-capture-operator),
which can be used to quickly generate anonymous functions that expect at least one argument.
The arguments can be accessed inside the _capture operator_ `&()` with `&X`, where
`X` refers to the input number of the argument.
There is no difference between
```elixir
add_capture = &(&1 + &2)
add_fn = fn a, b -> a + b end
```
Before we go any further let's take a quick look at the `calc_product` function.
You will see that there are 2 definitions for this function. One which takes a
list and another which takes an integer and turns it into a range. Other than
this, the functions work in exactly the same way. They both call reduce on an
enumerable and multiply the current value with the accumulator.
(The reason both work the same way is so that we could see the effect multiple
processes running concurrently have on how long it takes for us to get the
results of our factorial. I didn't want differences in a functions approach
to be the reason for changes in time. Also these factorial functions are not
perfect and do not need to be. That is not what we are testing here.)
Now we can test if our `calc_product` function works as expected. In your `iex`
shell load the `Factorial` module with `c("factorial.exs")`. Now type
`Factorial.calc_product(5)`. If you get an output of `120` then everything is
working as expected and you just solved a factorial on a single process.
This works well on a smaller scale but what if we need/want to work out
`factorial(100_000)`. If we use this approach it will take quite some time
before it we get the answer returned (something we will log a little later).
The reason for this is because this massive sum is being run on a single
process.
This is where spawning multiple processes comes in. By spawning multiple
processes, instead of giving all of the work to a single process, we can share
the load between any number of processes. This way each process is only handling
a portion of the work and we should be able to get our solution faster.
This sounds good in theory but let's see if we can put it into practice.
First, let's look through the `spawn` function and try to work out what it is
doing exactly.
The function starts by converting an integer into a range which it then
'[chunks](https://hexdocs.pm/elixir/Enum.html#chunk_every/4)' into a list of
lists with 4 elements.
The number 4 itself is not important, it could have been 5, 10, or 1000. What is
important about it, is that it influences the number of processes we will be spawning.
The larger the size of the 'chunks' the fewer processes are spawned.
Next, we map over the 'chunked' range and call the spawn function. This
spawns a new process for each chunked list running the `_spawn_function/1`.
Afterwards, the process running the `spawn/1` function sends the newly
created process a message and waits for a response message.
The `_spawn_function` function is pretty simple. It uses the exact same pattern
we used in our `add` function earlier. It receives a message with the senders
PID and then sends a message back to them. The message it sends back is the
result of the `calc_product` function.
Once each process in the map function has received a result, we then call the
`calc_product` once more to turn the list of results from map into a single integer,
the factorial.
In total the `spawn/1` function will end up calling
`calc_product` for a list with `n` elements:
`n % 4 + 1` if `n % 4 == 0` else `n % 4 + 2` times.
Remember, we split the original list into lists of 4 elements.
The only exception is the last chunk, which may contain fewer elements:
`[1, 2, 3, 4, 5] -> [[1, 2, 3, 4], [5]]`
For each chunked list we call `calc_product` and to calculate the final result,
the factorial, once.
Now that we have been through the code the only things left are to run the code
and to time the code.
To time the execution of our code,
add the following to your `factorial.exs` file:
```elixir
# just a helper function used to time the other functions
def run(f_name, args) do
:timer.tc(Factorial, f_name, args)
|> elem(0) # only displays the time as I didn't want to log numbers that could have thousands of digits
|> IO.inspect(label: "----->")
end
```
You can feel free to comment out the `|> elem(0)` line. I left it in because we
are about to have a MASSIVE number log in our terminal and we don't really need
to see it.
Now we have all the code we will need. All that's left is to call the code.
Let's go back to our `iex` shell and retype the `c("factorial.exs")` command.
Now type the following `Factorial.run(:calc_product, [10_000])`. You should get
a log of the number of milliseconds it took to run the function.
Next type `Factorial.run(:spawn, [10_000])`. Compare to two logs. You should
have something that looks like this...
.
Feel free to try this test again with even larger numbers (if you don't mind the
wait of course).
## tl;dr
> **_Note_**: this is _definitely **not**_ a "_reason_" to switch programming
> languages, but _one_ of our (_totally unscientific_) reasons for deciding
> to _investigate_ other options for programming languages was the fact
> that JavaScript (_with the introduction of ES2015_) now has
> **_Six Ways to Declare a Function_**:
> https://rainsoft.io/6-ways-to-declare-javascript-functions/
> which means that there is _ambiguity_ and "_debate_" as to which is
> "_best practice_", Go, **`Elixir`** and Rust don't suffer from this problem.
> Sure there are "_anonymous_" functions in Elixir
> (_required for functional programming_!) but there are still only **_Two Ways_**
> to define a `function` (_and both have specific use-cases_),
> which is _way_ easier to explain to a _beginner_ than the JS approach.
> see:
> http://stackoverflow.com/questions/18011784/why-are-there-two-kinds-of-functions-in-elixir
## Further resources:
- [Crash Course in Elixir](http://elixir-lang.org/crash-course.html)
- [Elixir School](https://elixirschool.com/),
which is available translated at least partially in over **20 languages**
and functions as a great succinct guide to core concepts.
- [30 Days of Elixir](https://github.com/seven1m/30-days-of-elixir)
is a walk through the **`Elixir`** language in 30 exercises.
- [Learn **`Elixir`** - List of Curated Resources](https://hackr.io/tutorials/learn-elixir)
- [Explanation video of **Pattern Matching** in Elixir](http://worldwide.chat/)
- Sign up to: https://elixirweekly.net/ for regular (_relevant_) updates!
- List of more [useful resources and sample apps](https://github.com/h4cc/awesome-elixir)
- If you want to know what's _next_ it's worth check out
[What's Ahead for Elixir?](https://youtu.be/A60nxws_iVs) (53 mins)
by **José Valim** (the creator of Elixir)
- _Interview_ with **José Valim** (the creator of Elixir) on _why_ he made it!
https://www.sitepoint.com/an-interview-with-elixir-creator-jose-valim/
- What was "_wrong_" with just writing directly in Erlang? read:
http://www.unlimitednovelty.com/2011/07/trouble-with-erlang-or-erlang-is-ghetto.html
- While **`Elixir`** by _itself_ is pretty _amazing_,
where the language really shines is in the **Phoenix Web Framework**!!
So once you know the basics of the language
[Learn `Phoenix` Web Development](https://github.com/dwyl/learn-phoenix-web-development).