- Why?
- What?
- How?
- Learn Elixir
- Commands
- Basic Types
- Functions and Modules
- Generate an Elixir Project
- Documentation
- Testing
- Formatting
- Publishing
- Data Structures
- Processes
- Further Resources
- Scalability
- Speed
- Compiled and run on the Erlang VM ("BEAM"). (Renowned for efficiency)
- Much better "garbage collection" than virtually any other VM
- Many tiny processes (as opposed to "threads" which are more difficult to manage)
- Functional language with dynamic typing
- Immutable data so "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.
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, 3 videos (25mins ๐ฅ plus exercises, totalling 90mins). The 'Try' course is free (there is an extended paid for course).
- Pete Broderick's Intro to Elixir (41 mins ๐ฅ)
- Jessica Kerr's Elixir Should Take Over the World (58 mins ๐ฅ)
Not a video learner? Looking for a specific learning? https://elixirschool.com/ is an excellent, free, open-source resource that explains all things Elixir ๐ โค๏ธ.
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:
Using the Homebrew package manager:
brew install elixir
- Add the Erlang Solutions repo:
wget https://packages.erlang-solutions.com/erlang-solutions_1.0_all.deb && sudo dpkg -i erlang-solutions_1.0_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
-
Web installer
- Download the installer
- Click next, next, ..., finish
-
Chocolatey (Package Manager)
choco install elixir
-
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 thefunction
name at any time to see documentation information about any given built-in function and how to use it. E.g If you typeh 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:
This section brings together the key information from Elixir's Getting Started 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
Type 1 + 2
into the terminal (after opening iex
):
iex> 1 + 2
3
More examples:
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
Elixir supports true
and false
as booleans.
iex> true
true
iex> false
false
iex> is_boolean(true)
true
iex> is_boolean(1)
false
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
nornil
- a value is falsy when it is
false
ornil
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 <function_name>/<number>
is the convention
used in Elixir to identify a function named
<function_name>
that takes <number>
parameters.
The value <number>
is also referred to as the function
arity.
In Elixir each function is identified univocally both by
its name and its arity. More information can be found here.
We can check the truthiness of a value by using the !/1
function twice.
Truthy values:
iex> !!true
true
iex> !!5
true
iex> !![1,2]
true
iex> !!"foo"
true
Falsy values (of which there are exactly two):
iex> !!false
false
iex> !!nil
false
Atoms are constants where their name is their own value (some other languages call these Symbols).
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.
iex> is_atom(MyApp.MyModule)
true
Atoms are also used to reference modules from Erlang libraries, including built-in ones.
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.
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.
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.
{: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 are surrounded by double quotes.
iex> "Hello World"
"Hello world"
# You can print a string using the `IO` module
iex> IO.puts "Hello world"
"Hello world"
:ok
Elixir uses square brackets to make a list.
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 and can use the Enum module to perform iterative functions such as mapping.
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.
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 and there are far fewer functions available
in the Tuple module. You can reference tuple values by index but you cannot iterate over them.
If you must treat your tuple as a list,
then convert it using Tuple.to_list(your_tuple)
If you need to iterate over the values use a list.
When dealing with large lists or tuples:
-
Updating
alist
(adding or removing elements) is fast -
Updating
atuple
is slow -
Reading
alist
(getting its length or selecting an element) is slow -
Reading
atuple
is fast
source: http://stackoverflow.com/questions/31192923/lists-vs-tuples-what-to-use-and-when
Anonymous functions start with fn
and end with end
.
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.
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 (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:
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
.
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
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,
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):
iex> Math.sum(1, 2)
3
To get started with your first Elixir project you need to make use of the Mix build tool that comes straight out of the box. 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 a project by typing the following command in your terminal, replacing [project_name] with the name of your project:
> mix new [project_name]
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:
* 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:
> 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
Open up the animals.ex
file in the lib directory. You should already see some hello-world
boilerplate like this:
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)
> iex -S mix
What this basically means is, "Start the elixir interactive terminal 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:
> Animals.hello
# :world
Let's start to create our own methods in the Animals
module. Replace the hello-world
method with the following:
@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:
> recompile()
Now we will have access to the create_zoo
method. Try it out in the command line:
> Animals.create_zoo
# ["lion", "tiger", "gorilla", "elephant", "monkey", "giraffe"]
Let's extend the Animals
module. Let's say that 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:
@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
methods that you can use on enumerables such as lists. Documentation for Enum
methods can be found here
Let's add another method to the Animals
module. Let's say that we want to find out if our zoo contains an animal:
@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: Let's create a function that takes a list of animals and the number of animals that you'd like to see and then returns a list of animals.
@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
What if we want to save our list of animals to a file? Let's write a function that will do this for us:
@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:
> 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 for example this is what gets returned for our animals file:
๏ฟฝl\๏ฟฝ๏ฟฝ๏ฟฝ๏ฟฝm๏ฟฝ๏ฟฝ๏ฟฝ๏ฟฝlionm๏ฟฝ๏ฟฝ๏ฟฝ๏ฟฝtigerm๏ฟฝ๏ฟฝ๏ฟฝ๏ฟฝgorillam๏ฟฝ๏ฟฝ๏ฟฝ๏ฟฝelephantm๏ฟฝ๏ฟฝ๏ฟฝ๏ฟฝmonkeym๏ฟฝ๏ฟฝ๏ฟฝ๏ฟฝgiraffej
@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 here allows us to pattern match against various options and react accordingly.
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:
@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.
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:
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:
> mix deps.get
You might receive an error saying: 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 then run the following command to generate
documentation (make sure you're not in iex
):
> 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!
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 like 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:
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):
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:
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
In Elixir version 1.6 the mix format
task was introduced.
see: elixir-lang/elixir#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:
mix format path/to/file.ex
Or you can define a pattern for types of files you want to check the format of:
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:
# 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:
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
To publish your Elixir package to Hex.pm:
- Check the version in
mix.exs
is up to date and that it follows the semantic versioning format:
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 advancedmix.exs
file where you can see this in action
-
Create a Hex.pm account if you do not have one already.
-
Make sure that ex_doc is added as a dependency in you project
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 replyY
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...
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
If you want to keep learning more Elixir, read on.
Maps are very similar to Object literals in JavaScript. They have almost the same
syntax except for a %
sign. They look like this:
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:
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:
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
Due to the immutability of Elixir, you cannot update a map using dot notation for example:
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
- Using a function
We can update a map usingMap.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:
iex> updatedAnimal = Map.put(animal, :name, "Max")
iex> updatedAnimal
# %{legs: 4, name: "Max", type: "dog"}
- Using syntax
We can use a special syntax for updating a map in Elixir. It looks like this:
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.
When looking into Elixir you may have heard about its processes and its support for concurrency. In fact we even mention processes as one of the key advantages elixir offers in this README. If you're anything like me then you are 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 well with the following...
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 description out of the way, let's start by spawning our first process.
Create a file called math.exs
and put the following in...
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
spawn(Math, :add, [1,2])
. You will see something that looks like this...
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 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 ๐ ๐ฅณ
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.
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...
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 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
which returns the PID
of the calling process (the PID of double).
We then call
receive 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
10
VERY COOL. We just spawned a process which did a task for us and returned the data.
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
and add the following code...
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,
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
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' 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 code add the following to your factorial.exs
file...
# 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).
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
- Crash Course in Elixir
- Elixir School, 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 is a walk through the Elixir language in 30 exercises.
- Learn Elixir - List of Curated Resources
- Elixir Courses at Classpert is a list of free and paid Online Courses
- Explanation video of Pattern Matching in Elixir
- Sign up to: https://elixirweekly.net/ for regular (relevant) updates!
- List of more useful resources and sample apps
- If you want to know what's next it's worth check out What's Ahead for Elixir? (53 mins) by Josรฉ Valim (the creator of Elixir)
- Interview with Josรฉ 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 try learning Phoenix.