Elixir/elixir-language.pdf.txt

Elixir Language

#elixir

Table of Contents

About

Chapter 1: Getting started with Elixir Language

Remarks

Versions

Examples

Hello World

Hello World from IEx

Chapter 2: Basic .gitignore for elixir program

Chapter 3: Basic .gitignore for elixir program

Remarks

Examples

A basic .gitignore for Elixir

Example

Standalone elixir application

Phoenix application

Auto-generated .gitignore

Chapter 4: basic use of guard clauses

Examples

basic uses of guard clauses

Chapter 5: BEAM

Examples

Introduction

Chapter 6: Behaviours

Examples

Introduction

Chapter 7: Better debugging with IO.inspect and labels

Introduction

Remarks

Examples

Without labels

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With labels

Chapter 8: Built-in types

Examples

Numbers

Atoms

Binaries and Bitstrings

Chapter 9: Conditionals

Remarks

Examples

case

if and unless

cond

with clause

Chapter 10: Constants

Remarks

Examples

Module-scoped constants

Constants as functions

Constants via macros

Chapter 11: Data Structures

Syntax

Remarks

Examples

Lists

Tuples

Chapter 12: Debugging Tips

Examples

Debugging with IEX.pry/0

Debugging with IO.inspect/1

Debug in pipe

Pry in pipe

Chapter 13: Doctests

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14

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25

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Examples

Introduction

Generating HTML documentation based on doctest

Multiline doctests

Chapter 14: Ecto

Examples

Adding a Ecto.Repo in an elixir program

"and" clause in a Repo.get_by/3

Querying with dynamic fields

Add custom data types to migration and to schema

Chapter 15: Erlang

Examples

Using Erlang

Inspect an Erlang module

Chapter 16: ExDoc

Examples

Introduction

Chapter 17: ExUnit

Examples

Asserting Exceptions

Chapter 18: Functional programming in Elixir

Introduction

Examples

Map

Reduce

Chapter 19: Functions

Examples

Anonymous Functions

Using the capture operator

Multiple bodies

Keyword lists as function parameters

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27

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30

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36

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37

37

Named Functions & Private Functions

Pattern Matching

Guard clauses

Default Parameters

Capture functions

Chapter 20: Getting help in IEx console

Introduction

Examples

Listing Elixir modules and functions

Chapter 21: IEx Console Tips & Tricks

Examples

Recompile project with `recompile`

See documentation with `h`

Get value from last command with `v`

Get the value of a previous command with `v`

Exit IEx console

See information with `i`

Creating PID

Have your aliases ready when you start IEx

Persistent history

When Elixir console is stuck...

break out of incomplete expression

Load a module or script into the IEx session

Chapter 22: Installation

Examples

Fedora Installation

OSX Installation

Homebrew

Macports

Debian/Ubuntu Installation

Gentoo/Funtoo Installation

Chapter 23: Join Strings

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Examples

Using String Interpolation

Using IO List

Using Enum.join

Chapter 24: Lists

Syntax

Examples

Keyword Lists

Char Lists

Cons Cells

Mapping Lists

List Comprehensions

Combined example

Summary

List difference

List Membership

Converting Lists to a Map

Chapter 25: Maps and Keyword Lists

Syntax

Remarks

Examples

Creating a Map

Creating a Keyword List

Difference between Maps and Keyword Lists

Chapter 26: Metaprogramming

Examples

Generate tests at compile time

Chapter 27: Mix

Examples

Create a Custom Mix Task

Custom mix task with command line arguments

Aliases

49

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Get help on available mix tasks

Chapter 28: Modules

Remarks

Module Names

Examples

List a module's functions or macros

Using modules

Delegating functions to another module

Chapter 29: Nodes

Examples

List all visible nodes in the system

Connecting nodes on the same machine

Connecting nodes on different machines

Chapter 30: Operators

Examples

The Pipe Operator

Pipe operator and parentheses

Boolean operators

Comparison operators

Join operators

'In' operator

Chapter 31: Optimization

Examples

Always measure first!

Chapter 32: Pattern matching

Examples

Pattern matching functions

Pattern matching on a map

Pattern matching on a list

Get the sum of a list using pattern matching

Anonymous functions

Tuples

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Reading a File

Pattern matching anonymous functions

Chapter 33: Polymorphism in Elixir

Introduction

Remarks

Examples

Polymorphism with Protocols

Chapter 34: Processes

Examples

Spawning a Simple Process

Sending and Receiving Messages

Recursion and Receive

Chapter 35: Protocols

Remarks

Examples

Introduction

Chapter 36: Sigils

Examples

Build a list of strings

Build a list of atoms

Custom sigils

Chapter 37: State Handling in Elixir

Examples

Managing a piece of state with an Agent

Chapter 38: Stream

Remarks

Examples

Chaining multiple operations

Chapter 39: Strings

Remarks

Examples

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Convert to string

Get a substring

Split a string

String Interpolation

Check if String contains Substring

Join Strings

Chapter 40: Task

Syntax

Parameters

Examples

Doing work in the background

Parallel processing

Chapter 41: Tips and Tricks

Introduction

Examples

Creating Custom Sigils and Documenting

Multiple [ OR ]

iex Custom Configuration - iex Decoration

Credits

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About

You can share this PDF with anyone you feel could benefit from it, downloaded the latest version 
from: elixir-language

It is an unofficial and free Elixir Language ebook created for educational purposes. All the content 
is extracted from Stack Overflow Documentation, which is written by many hardworking individuals 
at Stack Overflow. It is neither affiliated with Stack Overflow nor official Elixir Language.

The content is released under Creative Commons BY-SA, and the list of contributors to each 
chapter are provided in the credits section at the end of this book. Images may be copyright of 
their respective owners unless otherwise specified. All trademarks and registered trademarks are 
the property of their respective company owners.

Use the content presented in this book at your own risk; it is not guaranteed to be correct nor 
accurate, please send your feedback and corrections to [email protected]

https://riptutorial.com/

1

Chapter 1: Getting started with Elixir 
Language

Remarks

Elixir is a dynamic, functional language designed for building scalable and maintainable 
applications.

Elixir leverages the Erlang VM, known for running low-latency, distributed and fault-tolerant 
systems, while also being successfully used in web development and the embedded software 
domain.

Versions

Version Release Date

0.9

1.0

1.1

1.2

1.3

1.4

2013-05-23

2014-09-18

2015-09-28

2016-01-03

2016-06-21

2017-01-05

Examples

Hello World

For installation instructions on elixir check here, it describes instructions related to different 
platforms.

Elixir is a programming language that is created using erlang, and uses erlang's BEAM runtime (like 
JVM for java).

We can use elixir in two modes: interactive shell iex or directly running using elixir command.

Place the following in a file named hello.exs:

IO.puts "Hello world!"

https://riptutorial.com/

2

From the command line, type the following command to execute the Elixir source file:

$ elixir hello.exs

This should output:

Hello world!

This is known as the scripted mode of Elixir. In fact, Elixir programs can also be compiled (and 
generally, they are) into bytecode for the BEAM virtual machine.

You can also use iex for interactive elixir shell (recommended), run the command you will get a 
prompt like this:

Interactive Elixir (1.3.4) - press Ctrl+C to exit (type h() ENTER for help) 
iex(1)>

Here you can try your elixir hello world examples:

iex(1)> IO.puts "hello, world" 
hello, world 
:ok 
iex(2)> 

You can also compile and run your modules through iex. For example, if you have a helloworld.ex 
that contains:

defmodule Hello do 
   def sample do 
       IO.puts "Hello World!" 
   end 
end

Through iex, do:

iex(1)> c("helloworld.ex") 
[Hello] 
iex(2)> Hello.sample 
Hello World!

Hello World from IEx

You can also use the IEx (Interactive Elixir) shell to evaluate expressions and execute code.

If you are on Linux or Mac, just type iex on your bash and press enter:

$ iex

If you are on a Windows machine, type:

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3

C:\ iex.bat

Then you will enter into the IEx REPL (Read, Evaluate, Print, Loop), and you can just type 
something like:

iex(1)> "Hello World" 
"Hello World"

If you want to load a script while opening an IEx REPL, you can do this:

$ iex script.exs

Given script.exs is your script. You can now call functions from the script in the console.

Read Getting started with Elixir Language online: https://riptutorial.com/elixir/topic/954/getting-
started-with-elixir-language

https://riptutorial.com/

4

Chapter 2: Basic .gitignore for elixir program

Read Basic .gitignore for elixir program online: https://riptutorial.com/elixir/topic/6493/basic--
gitignore-for-elixir-program

https://riptutorial.com/

5

Chapter 3: Basic .gitignore for elixir program

Remarks

Note that the /rel folder may not be needed in your .gitignore file. This is generated if you are 
using a release management tool such as exrm

Examples

A basic .gitignore for Elixir

/_build 
/cover 
/deps 
erl_crash.dump 
*.ez 

# Common additions for various operating systems: 
# MacOS 
.DS_Store 

# Common additions for various editors: 
# JetBrains IDEA, IntelliJ, PyCharm, RubyMine etc. 
.idea 

Example

### Elixir ### 
/_build 
/cover 
/deps 
erl_crash.dump 
*.ez 

### Erlang ### 
.eunit 
deps 
*.beam 
*.plt 
ebin 
rel/example_project 
.concrete/DEV_MODE 
.rebar

Standalone elixir application

/_build 
/cover 
/deps 
erl_crash.dump 
*.ez 

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/rel

Phoenix application

/_build 
/db 
/deps 
/*.ez 
erl_crash.dump 
/node_modules 
/priv/static/ 
/config/prod.secret.exs 
/rel

Auto-generated .gitignore

By default, mix new <projectname> will generate a .gitignore file in the project root that is suitable 
for Elixir.

# The directory Mix will write compiled artifacts to. 
/_build 

# If you run "mix test --cover", coverage assets end up here. 
/cover 

# The directory Mix downloads your dependencies sources to. 
/deps 

# Where 3rd-party dependencies like ExDoc output generated docs. 
/doc 

# If the VM crashes, it generates a dump, let's ignore it too. 
erl_crash.dump 

# Also ignore archive artifacts (built via "mix archive.build"). 
*.ez

Read Basic .gitignore for elixir program online: https://riptutorial.com/elixir/topic/6526/basic--
gitignore-for-elixir-program

https://riptutorial.com/

7

 
 
 
 
 
Chapter 4: basic use of guard clauses

Examples

basic uses of guard clauses

In Elixir, one can create multiple implementations of a function with the same name, and specify 
rules which will be applied to the parameters of the function before calling the function in order to 
determine which implementation to run.

These rules are marked by the keyword when, and they go between the def function_name(params) 
and the do in the function definition. A trivial example:

defmodule Math do 

  def is_even(num) when num === 1 do 
    false 
  end 
  def is_even(num) when num === 2 do 
    true 
  end 

  def is_odd(num) when num === 1 do 
    true 
  end 
  def is_odd(num) when num === 2 do 
    false 
  end 

end

Say I run Math.is_even(2) with this example. There are two implementations of is_even, with 
differing guard clauses. The system will look at them in order, and run the first implementation 
where the parameters satisfy the guard clause. The first one specifies that num === 1 which is not 
true, so it moves on to the next one. The second one specifies that num === 2, which is true, so this 
is the implementation that is used, and the return value will be true.

What if I run Math.is_odd(1)? The system looks at the first implementation, and sees that since num 
is 1 the guard clause of the first implementation is satisfied. It will then use that implementation 
and return true, and not bother looking at any other implementations.

Guards are limited in the types of operations they can run. The Elixir documentation lists every 
allowed operation; in a nutshell they allow comparisons, math, binary operations, type-checking 
(e.g. is_atom), and a handful of small convenience functions (e.g. length). It is possible to define 
custom guard clauses, but it requires creating macros and is best left for a more advanced guide.

Note that guards do not throw errors; they are treated as normal failures of the guard clause, and 
the system moves on to look at the next implementation. If you find that you're getting 
(FunctionClauseError) no function clause matching when calling a guarded function with params 

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8

 
 
 
you expect to work, it may be that a guard clause which you expect to work is throwing an error 
which is being swallowed up.

To see this for yourself, create and then call a function with a guard which makes no sense, such 
as this which tries to divide by zero:

defmodule BadMath do 
  def divide(a) when a / 0 === :foo do 
    :bar 
  end 
end

Calling BadMath.divide("anything") will provide the somewhat-unhelpful error (FunctionClauseError) 
no function clause matching in BadMath.divide/1 — whereas if you had tried to run "anything" / 0 
directly, you would get a more helpful error: (ArithmeticError) bad argument in arithmetic 
expression.

Read basic use of guard clauses online: https://riptutorial.com/elixir/topic/6121/basic-use-of-guard-
clauses

https://riptutorial.com/

9

Chapter 5: BEAM

Examples

Introduction

iex> :observer.start 
:ok

:observer.start opens the GUI observer interface, showing you CPU breakdown, memory usage, 
and other information critical to understanding the usage patterns of your applications.

Read BEAM online: https://riptutorial.com/elixir/topic/3587/beam

https://riptutorial.com/

10

Chapter 6: Behaviours

Examples

Introduction

Behaviours are a list of functions specifications that another module can implement. They are 
similar to interfaces in other languages.

Here’s an example behaviour:

defmodule Parser do 
  @callback parse(String.t) :: any 
  @callback extensions() :: [String.t] 
end

And a module that implements it:

defmodule JSONParser do 
  @behaviour Parser 

  def parse(str), do: # ... parse JSON 
  def extensions, do: ["json"] 
end

The @behaviour module attribute above indicates that this module is expected to define every 
function defined in the Parser module. Missing functions will result in undefined behaviour function 
compilation errors.

Modules can have multiple @behaviour attributes.

Read Behaviours online: https://riptutorial.com/elixir/topic/3558/behaviours

https://riptutorial.com/

11

 
Chapter 7: Better debugging with IO.inspect 
and labels

Introduction

IO.inspect is very useful when you try to debug your chains of method calling. It can get messy 
though if you use it too often.

Since Elixir 1.4.0 the label option of IO.inspect can help

Remarks

Only works with Elixir 1.4+, but I can't tag that yet.

Examples

Without labels

url 
  |> IO.inspect 
  |> HTTPoison.get! 
  |> IO.inspect 
  |> Map.get(:body) 
  |> IO.inspect 
  |> Poison.decode! 
  |> IO.inspect

This will result in a lot of output with no context:

"https://jsonplaceholder.typicode.com/posts/1" 
%HTTPoison.Response{body: "{\n  \"userId\": 1,\n  \"id\": 1,\n  \"title\": \"sunt aut facere 
repellat provident occaecati excepturi optio reprehenderit\",\n  \"body\": \"quia et 
suscipit\\nsuscipit recusandae consequuntur expedita et cum\\nreprehenderit molestiae ut ut 
quas totam\\nnostrum rerum est autem sunt rem eveniet architecto\"\n}", 
 headers: [{"Date", "Thu, 05 Jan 2017 14:29:59 GMT"}, 
  {"Content-Type", "application/json; charset=utf-8"}, 
  {"Content-Length", "292"}, {"Connection", "keep-alive"}, 
  {"Set-Cookie", 
   "__cfduid=d56d1be0a544fcbdbb262fee9477600c51483626599; expires=Fri, 05-Jan-18 14:29:59 GMT; 
path=/; domain=.typicode.com; HttpOnly"}, 
  {"X-Powered-By", "Express"}, {"Vary", "Origin, Accept-Encoding"}, 
  {"Access-Control-Allow-Credentials", "true"}, 
  {"Cache-Control", "public, max-age=14400"}, {"Pragma", "no-cache"}, 
  {"Expires", "Thu, 05 Jan 2017 18:29:59 GMT"}, 
  {"X-Content-Type-Options", "nosniff"}, 
  {"Etag", "W/\"124-yv65LoT2uMHrpn06wNpAcQ\""}, {"Via", "1.1 vegur"}, 
  {"CF-Cache-Status", "HIT"}, {"Server", "cloudflare-nginx"}, 
  {"CF-RAY", "31c7a025e94e2d41-TXL"}], status_code: 200} 
"{\n  \"userId\": 1,\n  \"id\": 1,\n  \"title\": \"sunt aut facere repellat provident 

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12

occaecati excepturi optio reprehenderit\",\n  \"body\": \"quia et suscipit\\nsuscipit 
recusandae consequuntur expedita et cum\\nreprehenderit molestiae ut ut quas totam\\nnostrum 
rerum est autem sunt rem eveniet architecto\"\n}" 
%{"body" => "quia et suscipit\nsuscipit recusandae consequuntur expedita et cum\nreprehenderit 
molestiae ut ut quas totam\nnostrum rerum est autem sunt rem eveniet architecto", 
  "id" => 1, 
  "title" => "sunt aut facere repellat provident occaecati excepturi optio reprehenderit", 
  "userId" => 1}

With labels

using the label option to add context can help a lot:

url 
  |> IO.inspect(label: "url") 
  |> HTTPoison.get! 
  |> IO.inspect(label: "raw http resonse") 
  |> Map.get(:body) 
  |> IO.inspect(label: "raw body") 
  |> Poison.decode! 
  |> IO.inspect(label: "parsed body") 

url: "https://jsonplaceholder.typicode.com/posts/1" 
raw http resonse: %HTTPoison.Response{body: "{\n  \"userId\": 1,\n  \"id\": 1,\n  \"title\": 
\"sunt aut facere repellat provident occaecati excepturi optio reprehenderit\",\n  \"body\": 
\"quia et suscipit\\nsuscipit recusandae consequuntur expedita et cum\\nreprehenderit 
molestiae ut ut quas totam\\nnostrum rerum est autem sunt rem eveniet architecto\"\n}", 
 headers: [{"Date", "Thu, 05 Jan 2017 14:33:06 GMT"}, 
  {"Content-Type", "application/json; charset=utf-8"}, 
  {"Content-Length", "292"}, {"Connection", "keep-alive"}, 
  {"Set-Cookie", 
   "__cfduid=d22d817e48828169296605d27270af7e81483626786; expires=Fri, 05-Jan-18 14:33:06 GMT; 
path=/; domain=.typicode.com; HttpOnly"}, 
  {"X-Powered-By", "Express"}, {"Vary", "Origin, Accept-Encoding"}, 
  {"Access-Control-Allow-Credentials", "true"}, 
  {"Cache-Control", "public, max-age=14400"}, {"Pragma", "no-cache"}, 
  {"Expires", "Thu, 05 Jan 2017 18:33:06 GMT"}, 
  {"X-Content-Type-Options", "nosniff"}, 
  {"Etag", "W/\"124-yv65LoT2uMHrpn06wNpAcQ\""}, {"Via", "1.1 vegur"}, 
  {"CF-Cache-Status", "HIT"}, {"Server", "cloudflare-nginx"}, 
  {"CF-RAY", "31c7a4b8ae042d77-TXL"}], status_code: 200} 
raw body: "{\n  \"userId\": 1,\n  \"id\": 1,\n  \"title\": \"sunt aut facere repellat 
provident occaecati excepturi optio reprehenderit\",\n  \"body\": \"quia et 
suscipit\\nsuscipit recusandae consequuntur expedita et cum\\nreprehenderit molestiae ut ut 
quas totam\\nnostrum rerum est autem sunt rem eveniet architecto\"\n}" 
parsed body: %{"body" => "quia et suscipit\nsuscipit recusandae consequuntur expedita et 
cum\nreprehenderit molestiae ut ut quas totam\nnostrum rerum est autem sunt rem eveniet 
architecto", 
  "id" => 1, 
  "title" => "sunt aut facere repellat provident occaecati excepturi optio reprehenderit", 
  "userId" => 1}

Read Better debugging with IO.inspect and labels online: 
https://riptutorial.com/elixir/topic/8725/better-debugging-with-io-inspect-and-labels

https://riptutorial.com/

13

 
Chapter 8: Built-in types

Examples

Numbers

Elixir comes with integers and floating point numbers. An integer literal can be written in 
decimal, binary, octal and hexadecimal formats.

iex> x = 291 
291 

iex> x = 0b100100011 
291 

iex> x = 0o443 
291 

iex> x = 0x123 
291

As Elixir uses bignum arithmetic, the range of integer is only limited by the available memory 
on the system.

Floating point numbers are double precision and follows IEEE-754 specification.

iex> x = 6.8 
6.8 

iex> x = 1.23e-11 
1.23e-11

Note that Elixir also supports exponent form for floats.

iex> 1 + 1 
2 

iex> 1.0 + 1.0 
2.0

First we added two integers numbers, and the result is an integer. Later we added two floating 
point numbers, and the result is a floating point number.

Dividing in Elixir always returns a floating point number:

iex> 10 / 2 
5.0

In the same way, if you add, subtract or multiply an integer by a floating point number the result 
will be floating point:

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iex> 40.0 + 2 
42.0 

iex> 10 - 5.0 
5.0 

iex> 3 * 3.0 
9.0

For integer division, one can use the div/2 function:

iex> div(10, 2) 
5

Atoms

Atoms are constants that represent a name of some thing. The value of an atom is it's name. An 
atom name starts with a colon.

:atom   # that's how we define an atom

An atom's name is unique. Two atoms with the same names always are equal.

iex(1)> a = :atom 
:atom 

iex(2)> b = :atom 
:atom 

iex(3)> a == b 
true 

iex(4)> a === b 
true

Booleans true and false, actually are atoms.

iex(1)> true == :true 
true 

iex(2)> true === :true 
true

Atoms are stored in special atoms table. It's very important to know that this table is not garbage-
collected. So, if you want (or accidentally it is a fact) constantly create atoms - it is a bad idea.

Binaries and Bitstrings

Binaries in elixir are created using the Kernel.SpecialForms construct <<>>.

They are a powerful tool which makes Elixir very useful for working with binary protocols and 
encodings.

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15

 
 
 
 
 
 
Binaries and bitstrings are specified using a comma delimited list of integers or variable values, 
bookended by "<<" and ">>". They are composed of 'units', either a grouping of bits or a grouping 
of bytes. The default grouping is a single byte (8 bits), specified using an integer:

<<222,173,190, 239>> # 0xDEADBEEF

Elixir strings also convert directly to binaries:

iex> <<0, "foo">> 
<<0, 102, 111, 111>>

You can add "specifiers" to each "segment" of a binary, allowing you to encode:

•
•
•

Data Type
Size
Endianness

These specifiers are encoded by following each value or variable with the "::" operator:

<<102::integer-native>> 
<<102::native-integer>> # Same as above 
<<102::unsigned-big-integer>> 
<<102::unsigned-big-integer-size(8)>> 
<<102::unsigned-big-integer-8>> # Same as above 
<<102::8-integer-big-unsigned>> 
<<-102::signed-little-float-64>> # -102 as a little-endian Float64 
<<-102::native-little-float-64>> # -102 as a Float64 for the current machine

The available data types you can use are:

•
•
•
•
•
•
•
•
•

integer
float
bits (alias for bitstring)
bitstring
binary
bytes (alias for binary)
utf8
utf16
utf32

Be aware that when specifying the 'size' of the binary segment, it varies according to the 'type' 
chosen in the segment specifier:

•
•
•

integer (default) 1 bit
float 1 bit
binary 8 bits

Read Built-in types online: https://riptutorial.com/elixir/topic/1774/built-in-types

https://riptutorial.com/

16

Chapter 9: Conditionals

Remarks

Note that the do...end syntax is syntactic sugar for regular keyword lists, so you can actually do 
this:

unless false, do: IO.puts("Condition is false") 
# Outputs "Condition is false" 

# With an `else`: 
if false, do: IO.puts("Condition is true"), else: IO.puts("Condition is false") 
# Outputs "Condition is false"

Examples

case

 case {1, 2} do 
  {3, 4} -> 
    "This clause won't match." 
  {1, x} -> 
    "This clause will match and bind x to 2 in this clause." 
  _ -> 
    "This clause would match any value." 
end

case is only used to match the given pattern of the particular data. Here , {1,2} is matching with 
different case pattern that is given in the code example.

if and unless

if true do 
    "Will be seen since condition is true." 
end 

if false do 
    "Won't be seen since condition is false." 
else 
    "Will be seen. 
end 

unless false do 
    "Will be seen." 
end 

unless true do 
    "Won't be seen." 
else 
    "Will be seen." 
end

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cond

cond do 
   0 == 1 -> IO.puts "0 = 1" 
   2 == 1 + 1 -> IO.puts "1 + 1 = 2" 
   3 == 1 + 2 -> IO.puts "1 + 2 = 3" 
end 

# Outputs "1 + 1 = 2" (first condition evaluating to true)

cond will raise a CondClauseError if no conditions are true.

cond do 
  1 == 2 -> "Hmmm" 
  "foo" == "bar" -> "What?" 
end 
# Error

This can be avoided by adding a condition that will always be true.

cond do 
  ... other conditions 
  true -> "Default value" 
end

Unless it is never expected to reach the default case, and the program should in fact crash at that 
point.

with clause

with clause is used to combine matching clauses. It looks like we combine anonymous functions 
or handle function with multiple bodies (matching clauses). Consider the case: we create a user, 
insert it into DB, then create greet email and then send it to the user.

Without the with clause we might write something like this (I omitted functions implementations):

case create_user(user_params) do 
  {:ok, user} -> 
    case Mailer.compose_email(user) do 
      {:ok, email} -> 
        Mailer.send_email(email) 
      {:error, reason} -> 
        handle_error 
    end 
  {:error, changeset} -> 
    handle_error 
end

Here we handle our business process's flow with case (it could be cond or if). That leads us to so-
called 'pyramid of doom', because we have to deal with possible conditions and decide: whether 
move further or not. It would be much nicer to rewrite this code with with statement:

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18

 
with {:ok, user} <- create_user(user_params), 
     {:ok, email} <- Mailer.compose_email(user) do 
  {:ok, Mailer.send_email} 
else 
  {:error, _reason} -> 
    handle_error 
end

In the code snippet above we've rewrite nested case clauses with with. Within with we invoke some 
functions (either anonymous or named) and pattern match on their outputs. If all matched, with 
return do block result, or else block result otherwise.

We can omit else so with will return either do block result or the first fail result.

So, the value of with statement is its do block result.

Read Conditionals online: https://riptutorial.com/elixir/topic/2118/conditionals

https://riptutorial.com/

19

Chapter 10: Constants

Remarks

So this is a summary analysis I've done based on the methods listed at How do you define 
constants in Elixir modules?. I'm posting it for a couple reasons:

•

•
•

Most Elixir documentation is quite thorough, but I found this key architectural decision 
lacking guidance - so I would have requested it as a topic.
I wanted to get a little visibility and comments from others about the topic.
I also wanted to test out the new SO Documentation workflow. ;)

I've also uploaded the entire code to the GitHub repo elixir-constants-concept.

Examples

Module-scoped constants

defmodule MyModule do 
  @my_favorite_number 13 
  @use_snake_case "This is a string (use double-quotes)" 
end

These are only accessible from within this module.

Constants as functions

Declare:

defmodule MyApp.ViaFunctions.Constants do 
  def app_version, do: "0.0.1" 
  def app_author, do: "Felix Orr" 
  def app_info, do: [app_version, app_author] 
  def bar, do: "barrific constant in function" 
end

Consume with require:

defmodule MyApp.ViaFunctions.ConsumeWithRequire do 
  require MyApp.ViaFunctions.Constants 

  def foo() do 
    IO.puts MyApp.ViaFunctions.Constants.app_version 
    IO.puts MyApp.ViaFunctions.Constants.app_author 
    IO.puts inspect MyApp.ViaFunctions.Constants.app_info 
  end 

  # This generates a compiler error, cannot invoke `bar/0` inside a guard. 
  # def foo(_bar) when is_bitstring(bar) do 

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  #   IO.puts "We just used bar in a guard: #{bar}" 
  # end 
end

Consume with import:

defmodule MyApp.ViaFunctions.ConsumeWithImport do 
  import MyApp.ViaFunctions.Constants 

  def foo() do 
    IO.puts app_version 
    IO.puts app_author 
    IO.puts inspect app_info 
  end 
end

This method allows for reuse of constants across projects, but they will not be usable within guard 
functions that require compile-time constants.

Constants via macros

Declare:

defmodule MyApp.ViaMacros.Constants do 
  @moduledoc """ 
  Apply with `use MyApp.ViaMacros.Constants, :app` or `import MyApp.ViaMacros.Constants, 
:app`. 

  Each constant is private to avoid ambiguity when importing multiple modules 
  that each have their own copies of these constants. 
  """ 

  def app do 
    quote do 
      # This method allows sharing module constants which can be used in guards. 
      @bar "barrific module constant" 
      defp app_version, do: "0.0.1" 
      defp app_author, do: "Felix Orr" 
      defp app_info, do: [app_version, app_author] 
    end 
  end 

  defmacro __using__(which) when is_atom(which) do 
    apply(__MODULE__, which, []) 
  end 
end

Consume with use:

defmodule MyApp.ViaMacros.ConsumeWithUse do 
  use MyApp.ViaMacros.Constants, :app 

  def foo() do 
    IO.puts app_version 
    IO.puts app_author 
    IO.puts inspect app_info 

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21

 
 
 
 
 
  end 

  def foo(_bar) when is_bitstring(@bar) do 
    IO.puts "We just used bar in a guard: #{@bar}" 
  end 
end

This method allows you to use the @some_constant inside guards. I'm not even sure that the 
functions would be strictly necessary.

Read Constants online: https://riptutorial.com/elixir/topic/6614/constants

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22

 
Chapter 11: Data Structures

Syntax

•

•

[head | tail] = [1, 2, 3, true] # one can use pattern matching to break up cons cells. This 
assigns head to 1 and tail to [2, 3, true]

%{d: val} = %{d: 1, e: true} # this assigns val to 1; no variable d is created because the d on 
the lhs is really just a symbol that is used to create the pattern %{:d => _} (note that hash 
rocket notation allows one to have non-symbols as keys for maps just like in ruby)

Remarks

As for which data structure to us here are some brief remarks.

If you need an array data structure if you're going to be doing a lot of writing use lists. If instead 
you are going to be doing a lot of read you should use tuples.

As for maps they are just simply how you do key value stores.

Examples

Lists

a = [1, 2, 3, true]

Note that these are stored in memory as linked lists. Id est this is a series of cons cells where the 
head (List.hd/1) is the value of first item of the list and the tail (List.tail/1) is the value of the rest of 
the list.

List.hd(a) = 1 
List.tl(a) = [2, 3, true]

Tuples

b = {:ok, 1, 2}

Tuples are the equivalent of arrays in other languages. They are stored contiguously in memory.

Read Data Structures online: https://riptutorial.com/elixir/topic/1607/data-structures

https://riptutorial.com/

23

Chapter 12: Debugging Tips

Examples

Debugging with IEX.pry/0

Debugging with IEx.pry/0 is quite simple.

1. 
2. 
3. 

require IEx in your module
Find the line of code you want to inspect
Add IEx.pry after the line

Now start your project (e.g. iex -S mix).

When the line with IEx.pry/0 is reached the program will stop and you have the chance to inspect. 
It is like a breakpoint in a traditional debugger.

When you are finished just type respawn into the console.

require IEx; 

defmodule Example do 
  def double_sum(x, y) do 
    IEx.pry 
    hard_work(x, y) 
  end 

  defp hard_work(x, y) do 
    2 * (x + y) 
  end 
end

Debugging with IO.inspect/1

It is possible to use IO.inspect/1 as a tool to debug an elixir program.

defmodule MyModule do 
  def myfunction(argument_1, argument_2) do 
    IO.inspect(argument_1) 
    IO.inspect(argument_2) 
  end 
end

It will print out argument_1 and argument_2 to the console. Since IO.inspect/1 returns its 
argument it is very easy to include it in function calls or pipelines without breaking the flow:

do_something(a, b) 
|> do_something_else(c) 

# can be adorned with IO.inspect, with no change in functionality: 

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24

 
 
 
do_something(IO.inspect(a), IO.inspect(b)) 
|> IO.inspect 
do_something(IO.inspect(c))

Debug in pipe

defmodule Demo do 
  def foo do 
    1..10 
    |> Enum.map(&(&1 * &1))          |> p 
    |> Enum.filter(&rem(&1, 2) == 0) |> p 
    |> Enum.take(3)                  |> p 
  end 

  defp p(e) do 
    require Logger 
    Logger.debug inspect e, limit: :infinity 
    e 
  end 
end

iex(1)> Demo.foo 

23:23:55.171 [debug] [1, 4, 9, 16, 25, 36, 49, 64, 81, 100] 

23:23:55.171 [debug] [4, 16, 36, 64, 100] 

23:23:55.171 [debug] [4, 16, 36] 

[4, 16, 36]

Pry in pipe

defmodule Demo do 
  def foo do 
    1..10 
    |> Enum.map(&(&1 * &1)) 
    |> Enum.filter(&rem(&1, 2) == 0) |> pry 
    |> Enum.take(3) 
  end 

  defp pry(e) do 
    require IEx 
    IEx.pry 
    e 
  end 
end

iex(1)> Demo.foo 
Request to pry #PID<0.117.0> at lib/demo.ex:11 

      def pry(e) do 
        require IEx 

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25

 
 
 
 
 
 
 
 
        IEx.pry 
        e 
      end 

Allow? [Yn] Y 

Interactive Elixir (1.3.2) - press Ctrl+C to exit (type h() ENTER for help) 
pry(1)> e 
[4, 16, 36, 64, 100] 
pry(2)> respawn 

Interactive Elixir (1.3.2) - press Ctrl+C to exit (type h() ENTER for help) 
[4, 16, 36] 
iex(1)>

Read Debugging Tips online: https://riptutorial.com/elixir/topic/2719/debugging-tips

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26

 
 
 
Chapter 13: Doctests

Examples

Introduction

When you document your code with @doc, you can supply code examples like so:

# myproject/lib/my_module.exs 

defmodule MyModule do 
  @doc """ 
  Given a number, returns `true` if the number is even, otherwise `false`. 

  ## Example 
    iex> MyModule.even?(2) 
    true 
    iex> MyModule.even?(3) 
    false 
  """ 
  def even?(number) do 
    rem(number, 2) == 0 
  end 
end

You can add the code examples as test cases into one of your test suites:

# myproject/test/doc_test.exs 

defmodule DocTest do 
  use ExUnit.Case 
  doctest MyModule 
end

Then, you can then run your tests with mix test.

Generating HTML documentation based on doctest

Because generating documentation is based on markdown, you have to do 2 things :

1/ Write your doctest and make your doctest examples clear to improve readability (It is better to 
give a headline, like "examples" or "tests"). When you write your tests, do not forget to give 4 
spaces to your tests code so that it will be formatting as code in the HTML documentation.

2/ Then, enter "mix docs" in console at the root of your elixir project to generate the HTML 
documentation in the doc directory located in the root of your elixir project. 
$> mix docs

Multiline doctests

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27

 
 
 
You can do a multiline doctest by using '...>' for the lines following the first

iex> Foo.Bar.somethingConditional("baz") 
...>   |> case do 
...>       {:ok, _} -> true 
...>       {:error, _} -> false 
...>      end 
true

Read Doctests online: https://riptutorial.com/elixir/topic/2708/doctests

https://riptutorial.com/

28

Chapter 14: Ecto

Examples

Adding a Ecto.Repo in an elixir program

This can be done in 3 steps :

1. 

You must define an elixir module which use Ecto.Repo and register your app as an otp_app.

defmodule Repo do 
  use Ecto.Repo, otp_app: :custom_app 
end

2. 

You must also define some config for the Repo which will allow you to connect to the 
database. Here is an example with postgres.

config :custom_app, Repo, 
   adapter: Ecto.Adapters.Postgres, 
   database: "ecto_custom_dev", 
   username: "postgres_dev", 
   password: "postgres_dev", 
   hostname: "localhost", 
  # OR use a URL to connect instead 
  url: "postgres://postgres_dev:postgres_dev@localhost/ecto_custom_dev"

3. 

Before using Ecto in your application, you need to ensure that Ecto is started before your 
app is started. It can be done with registering Ecto in lib/custom_app.ex as a supervisor.

    def start(_type, _args) do 
      import Supervisor.Spec 

      children = [ 
       supervisor(Repo, []) 
      ] 

      opts = [strategy: :one_for_one, name: MyApp.Supervisor] 
      Supervisor.start_link(children, opts) 
    end

"and" clause in a Repo.get_by/3

If you have an Ecto.Queryable, named Post, which has a title and an description.

You can fetch the Post with title: "hello" and description : "world" by performing :

 MyRepo.get_by(Post, [title: "hello", description: "world"])

All of this is possible because Repo.get_by expects in second argument a Keyword List.

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29

 
 
Querying with dynamic fields

To query a field which name is contained in a variable, use the field function.

some_field = :id 
some_value = 10 

from p in Post, where: field(p, ^some_field) == ^some_value

Add custom data types to migration and to schema

(From this answer)

The example below adds an enumerated type to a postgres database.

First, edit the migration file (created with mix ecto.gen.migration):

def up do 
  # creating the enumerated type 
  execute("CREATE TYPE post_status AS ENUM ('published', 'editing')") 

  # creating a table with the column 
  create table(:posts) do 
    add :post_status, :post_status, null: false 
  end 
end 

def down do 
  drop table(:posts) 
  execute("DROP TYPE post_status") 
end

Second, in the model file either add a field with an Elixir type :

schema "posts" do 
  field :post_status, :string 
end

or implement the Ecto.Type behaviour.

A good example for the latter is the ecto_enum package and it can be used as a template. Its usage 
is well documented on its github page.

This commit shows an example usage in a Phoenix project from adding enum_ecto to the project 
and using the enumerated type in views and models.

Read Ecto online: https://riptutorial.com/elixir/topic/6524/ecto

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30

 
 
 
Chapter 15: Erlang

Examples

Using Erlang

Erlang modules are available as atoms. For example, the Erlang math module is available as 
:math:

iex> :math.pi 
3.141592653589793

Inspect an Erlang module

Use module_info on Erlang modules you wish to inspect:

iex> :math.module_info 
 [module: :math, 
  exports: [pi: 0, module_info: 0, module_info: 1, pow: 2, atan2: 2, sqrt: 1, 
   log10: 1, log2: 1, log: 1, exp: 1, erfc: 1, erf: 1, atanh: 1, atan: 1, 
   asinh: 1, asin: 1, acosh: 1, acos: 1, tanh: 1, tan: 1, sinh: 1, sin: 1, 
   cosh: 1, cos: 1], 
  attributes: [vsn: [113168357788724588783826225069997113388]], 
  compile: [options: [{:outdir, 
     '/private/tmp/erlang20160316-36404-xtp7cq/otp-OTP-18.3/lib/stdlib/src/../ebin'}, 
    {:i, 
     '/private/tmp/erlang20160316-36404-xtp7cq/otp-OTP-18.3/lib/stdlib/src/../include'}, 
    {:i, 
     '/private/tmp/erlang20160316-36404-xtp7cq/otp-OTP-
18.3/lib/stdlib/src/../../kernel/include'}, 
    :warnings_as_errors, :debug_info], version: '6.0.2', 
   time: {2016, 3, 16, 16, 40, 35}, 
   source: '/private/tmp/erlang20160316-36404-xtp7cq/otp-OTP-18.3/lib/stdlib/src/math.erl'], 
  native: false, 
  md5: <<85, 35, 110, 210, 174, 113, 103, 228, 63, 252, 81, 27, 224, 15, 64, 
    44>>]

Read Erlang online: https://riptutorial.com/elixir/topic/2716/erlang

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31

Chapter 16: ExDoc

Examples

Introduction

To generate documentation in HTML format from @doc and @moduledoc attributes in your source code, 
add ex_doc and a markdown processor, right now ExDoc supports Earmark, Pandoc, Hoedown 
and Cmark, as dependencies into your mix.exs file:

# config/mix.exs 

def deps do 
  [{:ex_doc, "~> 0.11", only: :dev}, 
   {:earmark, "~> 0.1", only: :dev}] 
end

If you want to use another Markdown processor, you can find more information in the Changing 
the Markdown tool section.

You can use Markdown within Elixir @doc and @moduledoc attributes.

Then, run mix docs.

One thing to keep in mind is that ExDoc allows configuration parameters, such as:

  def project do 
    [app: :my_app, 
     version: "0.1.0-dev", 
     name: "My App", 
     source_url: "https://github.com/USER/APP", 
     homepage_url: "http://YOUR_PROJECT_HOMEPAGE", 
     deps: deps(), 
     docs: [logo: "path/to/logo.png", 
            output: "docs", 
            main: "README", 
            extra_section: "GUIDES", 
            extras: ["README.md", "CONTRIBUTING.md"]]] 
  end

You can see more information about this configuration options with mix help docs

Read ExDoc online: https://riptutorial.com/elixir/topic/3582/exdoc

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32

 
Chapter 17: ExUnit

Examples

Asserting Exceptions

Use assert_raise to test if an exception was raised. assert_raise takes in an Exception and a 
function to be executed.

  test "invalid block size" do 
    assert_raise(MerkleTree.ArgumentError, (fn() -> MerkleTree.new ["a", "b", "c"] end)) 
  end

Wrap any code you want to test in an anonymous function and pass it to assert_raise.

Read ExUnit online: https://riptutorial.com/elixir/topic/3583/exunit

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33

Chapter 18: Functional programming in Elixir

Introduction

Let's try to implement the basic higher orders functions like map and reduce using Elixir

Examples

Map

Map is a function which will take an array and a function and return an array after applying that 
function to each element in that list

defmodule MyList do 
  def map([], _func) do 
    [] 
  end 

  def map([head | tail], func) do 
    [func.(head) | map(tail, func)] 
  end 
end

Copy paste in iex and execute:

MyList.map [1,2,3], fn a -> a * 5 end

Shorthand syntax is MyList.map [1,2,3], &(&1 * 5)

Reduce

Reduce is a function which will take an array, function and accumulator and use accumulator as 
seed to start the iteration with the first element to give next accumulator and the iteration 
continues for all the elements in the array (refer below example)

defmodule MyList do 
  def reduce([], _func, acc) do 
    acc 
  end 

  def reduce([head | tail], func, acc) do 
    reduce(tail, func, func.(acc, head)) 
  end 
end

Copy paste the above snippet in iex:

1. 

To add all numbers in an array: MyList.reduce [1,2,3,4], fn acc, element -> acc + element 
end, 0

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34

 
 
2. 

To mutliply all numbers in an array: MyList.reduce [1,2,3,4], fn acc, element -> acc * 
element end, 1

Explanation for example 1:

Iteration 1 => acc = 0, element = 1 ==> 0 + 1 ===> 1 = next accumulator 
Iteration 2 => acc = 1, element = 2 ==> 1 + 2 ===> 3 = next accumulator 
Iteration 3 => acc = 3, element = 3 ==> 3 + 3 ===> 6 = next accumulator 
Iteration 4 => acc = 6, element = 4 ==> 6 + 4 ===> 10 = next accumulator = result(as all 
elements are done)

Filter the list using reduce

MyList.reduce [1,2,3,4], fn acc, element -> if rem(element,2) == 0 do acc else acc ++ 
[element] end end, []

Read Functional programming in Elixir online: https://riptutorial.com/elixir/topic/10186/functional-
programming-in-elixir

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35

Chapter 19: Functions

Examples

Anonymous Functions

In Elixir, a common practice is to use anonymous functions. Creating an anonymous function is 
simple:

iex(1)> my_func = fn x -> x * 2 end 
#Function<6.52032458/1 in :erl_eval.expr/5>

The general syntax is:

fn args -> output end

For readability, you may put parenthesis around the arguments:

iex(2)> my_func = fn (x, y) -> x*y end 
#Function<12.52032458/2 in :erl_eval.expr/5>

To invoke an anonymous function, call it by the assigned name and add . between the name and 
arguments.

iex(3)>my_func.(7, 5) 
35

It is possible to declare anonymous functions without arguments:

iex(4)> my_func2 = fn -> IO.puts "hello there" end 
iex(5)> my_func2.() 
hello there 
:ok

Using the capture operator

To make anonymous functions more concise you can use the capture operator &. For example, 
instead of:

iex(5)> my_func = fn (x) -> x*x*x end

You can write:

iex(6)> my_func = &(&1*&1*&1)

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36

With multiple parameters, use the number corresponding to each argument, counting from 1:

iex(7)> my_func = fn (x, y) -> x + y end 

iex(8)> my_func = &(&1 + &2)   # &1 stands for x and &2 stands for y 

iex(9)> my_func.(4, 5) 
9

Multiple bodies

An anonymous function can also have multiple bodies (as a result of pattern matching):

my_func = fn 
  param1 -> do_this 
  param2 -> do_that 
end

When you call a function with multiple bodies Elixir attempts to match the parameters you have 
provided with the proper function body.

Keyword lists as function parameters

Use keyword lists for 'options'-style parameters that contains multiple key-value pairs:

def myfunc(arg1, opts \\ []) do 
  # Function body 
end

We can call the function above like so:

iex> myfunc "hello", pizza: true, soda: false

which is equivalent to:

iex> myfunc("hello", [pizza: true, soda: false])

The argument values are available as opts.pizza and opts.soda respectively. 
Alternatively, you could use atoms: opts[:pizza] and opts[:soda].

Named Functions & Private Functions

Named Functions

defmodule Math do 
    # one way 
    def add(a, b) do 
        a + b 

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37

 
 
    end 

    # another way 
    def subtract(a, b), do: a - b 
end 

iex> Math.add(2, 3) 
5 
:ok 
iex> Math.subtract(5, 2) 
3 
:ok

Private Functions

defmodule Math do 
    def sum(a, b) do 
        add(a, b) 
    end 

    # Private Function 
    defp add(a, b) do 
        a + b 
    end 
end 

iex> Math.add(2, 3) 
** (UndefinedFunctionError) undefined function Math.add/2 
Math.add(3, 4) 
iex> Math.sum(2, 3) 
5

Pattern Matching

Elixir matches a function call to its body based on the value of its arguments.

defmodule Math do 
    def factorial(0): do: 1 
    def factorial(n): do: n * factorial(n - 1) 
end

Here, factorial of positive numbers matches the second clause, while factorial(0) matches the 
first. (ignoring negative numbers for the sake of simplicity). Elixir tries to match the functions from 
top to bottom. If the second function is written above the first, we will an unexpected result as it 
goes to an endless recursion. Because factorial(0) matches to factorial(n)

Guard clauses

Guard clauses enables us to check the arguments before executing the function. Guard clauses 
are usually preferred to if and cond due to their readability, and to make a certain optimization 
technique easier for the compiler. The first function definition where all guards match is executed.

Here is an example implementation of the factorial function using guards and pattern matching.

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38

 
 
 
 
defmodule Math do 
    def factorial(0), do: 1 
    def factorial(n) when n > 0: do: n * factorial(n - 1) 
end

The first pattern matches if (and only if) the argument is 0. If the argument is not 0, the pattern 
match fails and the next function below is checked.

That second function definition has a guard clause: when n > 0. This means that this function only 
matches if the argument n is greater than 0. After all, the mathematical factorial function is not 
defined for negative integers.

If neither function definition (including their pattern matching and guard clauses) match, a 
FunctionClauseError will be raised. This happens for this function when we pass a negative number 
as the argument, since it is not defined for negative numbers.

Note that this FunctionClauseError itself, is not a mistake. Returning -1 or 0 or some other "error 
value" as is common in some other languages would hide the fact that you called an undefined 
function, hiding the source of the error, possibly creating a huge painful bug for a future developer.

Default Parameters

You can pass default parameters to any named function using the syntax: param \\ value:

defmodule Example do 
    def func(p1, p2 \\ 2) do 
        IO.inspect [p1, p2] 
    end 
end 

Example.func("a")    # => ["a", 2] 
Example.func("b", 4) # => ["b", 4]

Capture functions

Use & to capture functions from other modules. You can use the captured functions directly as 
function parameters or within anonymous functions.

Enum.map(list, fn(x) -> String.capitalize(x) end)

Can be made more concise using &:

Enum.map(list, &String.capitalize(&1))

Capturing functions without passing any arguments require you to explicitly specify its arity, e.g. 
&String.capitalize/1:

defmodule Bob do 
  def say(message, f \\ &String.capitalize/1) do 
    f.(message) 

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  end 
end

Read Functions online: https://riptutorial.com/elixir/topic/2442/functions

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Chapter 20: Getting help in IEx console

Introduction

IEx provides access to Elixir documentation. When Elixir is installed on your system you can start 
IEx e.g. with iex command in a terminal. Then type h command on IEx command line followed by 
the function name prepended by its module name e.g. h List.foldr

Examples

Listing Elixir modules and functions

To get the list of Elixir modules just type

h Elixir.[TAB]

Pressing [TAB] autocompletes modules and functions names. In this case it lists all modules. To 
find all functions in a module e.g. List use

h List.[TAB]

Read Getting help in IEx console online: https://riptutorial.com/elixir/topic/10780/getting-help-in-
iex-console

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Chapter 21: IEx Console Tips & Tricks

Examples

Recompile project with `recompile`

iex(1)> recompile 
Compiling 1 file (.ex) 
:ok

See documentation with `h`

iex(1)> h List.last 

                                 def last(list) 

Returns the last element in list or nil if list is empty. 

Examples 

┃ iex> List.last([]) 
┃ nil 
┃ 
┃ iex> List.last([1]) 
┃ 1 
┃ 
┃ iex> List.last([1, 2, 3]) 
┃ 3

Get value from last command with `v`

iex(1)> 1 + 1 
2 
iex(2)> v 
2 
iex(3)> 1 + v 
3

See also: Get the value of a row with `v`

Get the value of a previous command with `v`

iex(1)> a = 10 
10 
iex(2)> b = 20 
20 
iex(3)> a + b 
30

You can get a specific row passing the index of the row:

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iex(4)> v(3) 
30

You can also specify an index relative to the current row:

iex(5)> v(-1) # Retrieves value of row (5-1) -> 4 
30 
iex(6)> v(-5) # Retrieves value of row (5-4) -> 1 
10

The value can be reused in other calculations:

iex(7)> v(2) * 4 
80

If you specify a non-existing row, IEx will raise an error:

iex(7)> v(100) 
** (RuntimeError) v(100) is out of bounds 
    (iex) lib/iex/history.ex:121: IEx.History.nth/2 
    (iex) lib/iex/helpers.ex:357: IEx.Helpers.v/1

Exit IEx console

1. 

Use Ctrl + C, Ctrl + C to exit

iex(1)> 
BREAK: (a)bort (c)ontinue (p)roc info (i)nfo (l)oaded 
       (v)ersion (k)ill (D)b-tables (d)istribution

2. 

Use Ctrl+ \ to immediately exit

See information with `i`

iex(1)> i :ok 
Term 
  :ok 
Data type 
  Atom 
Reference modules 
  Atom 
iex(2)> x = "mystring" 
"mystring" 
iex(3)> i x 
Term 
  "mystring" 
Data type 
  BitString 
Byte size 
  8 
Description 
  This is a string: a UTF-8 encoded binary. It's printed surrounded by 
  "double quotes" because all UTF-8 encoded codepoints in it are printable. 

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Raw representation 
  <<109, 121, 115, 116, 114, 105, 110, 103>> 
Reference modules 
  String, :binary

Creating PID

This is useful when you didn't store the PID from a previous command

iex(1)> self() 
#PID<0.138.0> 
iex(2)> pid("0.138.0") 
#PID<0.138.0> 
iex(3)> pid(0, 138, 0) 
#PID<0.138.0>

Have your aliases ready when you start IEx

If you put your commonly used aliases into an .iex.exs file at the root of your app, IEx will load 
them for you on startup.

alias App.{User, Repo}

Persistent history

By default, user input history in IEx do not persist across different sessions.

erlang-history adds history support to both the Erlang shell and IEx:

git clone [email protected]:ferd/erlang-history.git 
cd erlang-history 
sudo make install

You can now access your previous inputs using the up and down arrow keys, even across 
different IEx sessions.

When Elixir console is stuck...

Sometimes you might accidentally run something in the shell that ends up waiting forever, and 
thus blocking the shell:

iex(2)> receive do _ -> :stuck end

In that case, press Ctrl-g. You'll see:

User switch command

Enter these commands in order:

•

k (to kill the shell process)

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•
•

s (to start a new shell process)
c (to connect to the new shell process)

You'll end up in a new Erlang shell:

Eshell V8.0.2  (abort with ^G) 
1>

To start an Elixir shell, type:

'Elixir.IEx.CLI':local_start().

(don't forget the final dot!)

Then you'll see a new Elixir shell process coming up:

Interactive Elixir (1.3.2) - press Ctrl+C to exit (type h() ENTER for help) 
iex(1)> "I'm back" 
"I'm back" 
iex(2)>

To escape from “awaiting-for-more-input” mode (due to unclosed quotation mark, bracket etc,) 
type #iex:break, followed by carriage return ((cid:0)):

iex(1)> "Hello, "world" 
...(1)> 
...(1)> #iex:break 
** (TokenMissingError) iex:1: incomplete expression 

iex(1)>

the above is specifically useful when copy-pasting a relatively huge snippet turns the console to 
“awaiting-for-more-input” mode.

break out of incomplete expression

When you have entered something into IEx which expects a completion, such as a multiline string, 
IEx will change the prompt to indicate that it is waiting for you finish by changing the prompt to 
have an ellipsis (...) rather than iex.

If you find that IEx is waiting for you to finish an expression but you aren't sure what it needs to 
terminate the expression, or you simply want to abort this line of input, enter #iex:break as the 
console input. This will cause IEx to throw a TokenMissingError and cancel waiting for any more 
input, returning you to a standard "top-level" console input.

iex:1> "foo" 
"foo" 
iex:2> "bar 
...:2> #iex:break 
** (TokenMissingError) iex:2: incomplete expression

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More info is available at the IEx documentation.

Load a module or script into the IEx session

If you have an elixir file; a script or a module and want to load it into the current IEx session, you 
can use the c/1 method:

iex(1)> c "lib/utils.ex" 
iex(2)> Utils.some_method

This will compile and load the module in IEx, and you'll be able to call all of it's public methods.

For scripts, it will immediately execute the contents of the script:

iex(3)> c "/path/to/my/script.exs" 
Called from within the script!

Read IEx Console Tips & Tricks online: https://riptutorial.com/elixir/topic/1283/iex-console-tips---
tricks

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Chapter 22: Installation

Examples

Fedora Installation

dnf install erlang elixir

OSX Installation

On OS X and MacOS, Elixir can be installed via the common package managers:

Homebrew

$ brew update 
$ brew install elixir 

Macports

 $ sudo port install elixir

Debian/Ubuntu Installation

# Fetch and install package to setup access to the official APT repository 
wget https://packages.erlang-solutions.com/erlang-solutions_1.0_all.deb 
sudo dpkg -i erlang-solutions_1.0_all.deb 

# Update package index 
sudo apt-get update 

# Install Erlang and Elixir 
sudo apt-get install esl-erlang 
sudo apt-get install elixir

Gentoo/Funtoo Installation

Elixir is available in main packages repository. 
Update the packages list before installing any package:

emerge --sync

This is one step installation:

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emerge --ask dev-lang/elixir

Read Installation online: https://riptutorial.com/elixir/topic/4208/installation

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Chapter 23: Join Strings

Examples

Using String Interpolation

iex(1)> [x, y] = ["String1", "String2"] 
iex(2)> "#{x} #{y}" 
# "String1 String2"

Using IO List

["String1", " ", "String2"] |> IO.iodata_to_binary 
# "String1 String2"

This will gives some performances boosts as strings not duplicated in memory. 
Alternative method:

iex(1)> IO.puts(["String1", " ", "String2"]) 
# String1 String2

Using Enum.join

Enum.join(["String1", "String2"], " ") 
# "String1 String2"

Read Join Strings online: https://riptutorial.com/elixir/topic/9202/join-strings

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Chapter 24: Lists

Syntax

•
•
•
•
•
•
•
•
•
•
•

[]
[1, 2, 3, 4]
[1, 2] ++ [3, 4] # -> [1,2,3,4]
hd([1, 2, 3, 4]) # -> 1
tl([1, 2, 3, 4]) # -> [2,3,4]
[head | tail]
[1 | [2, 3, 4]] # -> [1,2,3,4]
[1 | [2 | [3 | [4 | []]]]] -> [1,2,3,4]
'hello' = [?h, ?e, ?l, ?l, ?o]
keyword_list = [a: 123, b: 456, c: 789]
keyword_list[:a] # -> 123

Examples

Keyword Lists

Keyword lists are lists where each item in the list is a tuple of an atom followed by a value.

keyword_list = [{:a, 123}, {:b, 456}, {:c, 789}]

A shorthand notation for writing keyword lists is as follows:

keyword_list = [a: 123, b: 456, c: 789]

Keyword lists are useful for creating ordered key-value pair data structures, where multiple items 
can exist for a given key.

The first item in a keyword list for a given key can be obtained like so:

iex> keyword_list[:b] 
456

A use case for keyword lists could be a sequence of named tasks to run:

defmodule TaskRunner do 
  def run_tasks(tasks) do 
    # Call a function for each item in the keyword list. 
    # Use pattern matching on each {:key, value} tuple in the keyword list 
    Enum.each(tasks, fn 
      {:delete, x} -> 
        IO.puts("Deleting record " <> to_string(x) <> "...") 
      {:add, value} -> 

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        IO.puts("Adding record \"" <> value <> "\"...") 
      {:update, {x, value}} -> 
        IO.puts("Setting record " <> to_string(x) <> " to \"" <> value <> "\"...") 
    end) 
  end 
end

This code can be called with a keyword list like so:

iex> tasks = [ 
...>   add: "foo", 
...>   add: "bar", 
...>   add: "test", 
...>   delete: 2, 
...>   update: {1, "asdf"} 
...> ] 

iex> TaskRunner.run_tasks(tasks) 
Adding record "foo"... 
Adding record "bar"... 
Adding record "test"... 
Deleting record 2... 
Setting record 1 to "asdf"...

Char Lists

Strings in Elixir are "binaries". However, in Erlang code, strings are traditionally "char lists", so 
when calling Erlang functions, you may have to use char lists instead of regular Elixir strings.

While regular strings are written using double quotes ", char lists are written using single quotes ':

string = "Hello!" 
char_list = 'Hello!'

Char lists are simply lists of integers representing the code points of each character.

'hello' = [104, 101, 108, 108, 111]

A string can be converted to a char list with to_charlist/1:

iex> to_charlist("hello") 
'hello'

And the reverse can be done with to_string/1:

iex> to_string('hello') 
"hello"

Calling an Erlang function and converting the output to a regular Elixir string:

iex> :os.getenv |> hd |> to_string 
"PATH=/usr/local/bin:/usr/bin:/bin"

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Cons Cells

Lists in Elixir are linked lists. This means that each item in a list consists of a value, followed by a 
pointer to the next item in the list. This is implemented in Elixir using cons cells.

Cons cells are simple data structures with a "left" and a "right" value, or a "head" and a "tail".

A | symbol can be added before the last item in a list to notate an (improper) list with a given head 
and tail. The following is a single cons cell with 1 as the head and 2 as the tail:

[1 | 2]

The standard Elixir syntax for a list is actually equivalent to writing a chain of nested cons cells:

[1, 2, 3, 4] = [1 | [2 | [3 | [4 | []]]]]

The empty list [] is used as the tail of a cons cell to represent the end of a list.

All lists in Elixir are equivalent to the form [head | tail], where head is the first item of the list and 
tail is the rest of the list, minus the head.

iex> [head | tail] = [1, 2, 3, 4] 
[1, 2, 3, 4] 
iex> head 
1 
iex> tail 
[2, 3, 4]

Using the [head | tail] notation is useful for pattern matching in recursive functions:

def sum([]), do: 0 

def sum([head | tail]) do 
  head + sum(tail) 
end

Mapping Lists

map is a function in functional programming which given a list and a function, returns a new list with 
the function applied to each item in that list. In Elixir, the map/2 function is in the Enum module.

iex> Enum.map([1, 2, 3, 4], fn(x) -> x + 1 end) 
[2, 3, 4, 5]

Using the alternative capture syntax for anonymous functions:

iex> Enum.map([1, 2, 3, 4], &(&1 + 1)) 
[2, 3, 4, 5]

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Referring to a function with capture syntax:

iex> Enum.map([1, 2, 3, 4], &to_string/1) 
["1", "2", "3", "4"]

Chaining list operations using the pipe operator:

iex> [1, 2, 3, 4] 
...> |> Enum.map(&to_string/1) 
...> |> Enum.map(&("Chapter " <> &1)) 
["Chapter 1", "Chapter 2", "Chapter 3", "Chapter 4"]

List Comprehensions

Elixir doesn't have loops. Instead of them for lists there are great Enum and List modules, but there 
are also List Comprehensions.

List Comprehensions can be useful to:

•

create new lists

iex(1)> for value <- [1, 2, 3], do: value + 1 
[2, 3, 4] 

•

filtering lists, using guard expressions but you use them without when keyword.

iex(2)> odd? = fn x -> rem(x, 2) == 1 end 
iex(3)> for value <- [1, 2, 3], odd?.(value), do: value 
[1, 3]

•

create custom map, using into keyword:

iex(4)> for value <- [1, 2, 3], into: %{}, do: {value, value + 1} 
%{1 => 2, 2=>3, 3 => 4}

Combined example

iex(5)> for value <- [1, 2, 3], odd?.(value), into: %{}, do: {value, value * value} 
%{1 => 1, 3 => 9}

Summary

List Comprehensions:

•

uses for..do syntax with additional guards after commas and into keyword when returning 
other structure than lists ie. map.

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•
•
•
•

in other cases return new lists
doesn't support accumulators
can't stop processing when certain condition is met
guard statements have to be first in order after for and before do or into symbols. Order of 
symbols doesn't matter

According to these constraints List Comprehensions are limited only for simple usage. In more 
advanced cases using functions from Enum and List modules would be the best idea.

List difference

iex> [1, 2, 3] -- [1, 3] 
[2]

-- removes the first occurrence of an item on the left list for each item on the right.

List Membership

Use in operator to check if an element is a member of a list.

iex> 2 in [1, 2, 3] 
true 
iex> "bob" in [1, 2, 3] 
false

Converting Lists to a Map

Use Enum.chunk/2 to group elements into sub-lists, and Map.new/2 to convert it into a Map:

[1, 2, 3, 4, 5, 6] 
|> Enum.chunk(2) 
|> Map.new(fn [k, v] -> {k, v} end)

Would give:

%{1 => 2, 3 => 4, 5 => 6}

Read Lists online: https://riptutorial.com/elixir/topic/1279/lists

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Chapter 25: Maps and Keyword Lists

Syntax

•
•
•
•

map = %{} // creates an empty map
map = %{:a => 1, :b => 2} // creates a non-empty map
list = [] // creates an empty list
list = [{:a, 1}, {:b, 2}] // creates a non-empty keyword list

Remarks

Elixir provides two associative data structures: maps and keyword lists.

Maps are the Elixir key-value (also called dictionary or hash in other languages) type.

Keyword lists are tuples of key/value that associate a value to a certain key. They are generally 
used as options for a function call.

Examples

Creating a Map

Maps are the Elixir key-value (also called dictionary or hash in other languages) type. You create a 
map using the %w{} syntax:

%{} // creates an empty map 
%{:a => 1, :b => 2} // creates a non-empty map

Keys and values can use be any type:

%{"a" => 1, "b" => 2} 
%{1 => "a", 2 => "b"}

Moreover, you can have maps with mixed types for both keys and values":

// keys are integer or strings 
%{1 => "a", "b" => :foo} 
// values are string or nil 
%{1 => "a", 2 => nil}

When all the keys in a map are atoms, you can use the keyword syntax for convenience:

%{a: 1, b: 2}

Creating a Keyword List

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Keyword lists are tuples of key/value, generally used as options for a function call.

[{:a, 1}, {:b, 2}] // creates a non-empty keyword list

Keyword lists can have the same key repeated more than once.

[{:a, 1}, {:a, 2}, {:b, 2}] 
[{:a, 1}, {:b, 2}, {:a, 2}]

Keys and values can be any type:

[{"a", 1}, {:a, 2}, {2, "b"}]

Difference between Maps and Keyword Lists

Maps and keyword lists have different application. For instance, a map cannot have two keys with 
the same value and it's not ordered. Conversely, a Keyword list can be a little bit hard to use in 
pattern matching in some cases.

Here's a few use cases for maps vs keyword lists.

Use keyword lists when:

•
•

you need the elements to be ordered
you need more than one element with the same key

Use maps when:

•
•
•

you want to pattern-match against some keys/values
you don't need more than one element with the same key
whenever you don't explicitly need a keyword list

Read Maps and Keyword Lists online: https://riptutorial.com/elixir/topic/2706/maps-and-keyword-
lists

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Chapter 26: Metaprogramming

Examples

Generate tests at compile time

defmodule ATest do 
  use ExUnit.Case 

  [{1, 2, 3}, {10, 20, 40}, {100, 200, 300}] 
  |> Enum.each(fn {a, b, c} -> 
    test "#{a} + #{b} = #{c}" do 
      assert unquote(a) + unquote(b) = unquote(c) 
    end 
  end) 
end

Output:

. 

  1) test 10 + 20 = 40 (Test.Test) 
     test.exs:6 
     match (=) failed 
     code: 10 + 20 = 40 
     rhs:  40 
     stacktrace: 
       test.exs:7 

. 

Finished in 0.1 seconds (0.1s on load, 0.00s on tests) 
3 tests, 1 failure

Read Metaprogramming online: https://riptutorial.com/elixir/topic/4069/metaprogramming

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Chapter 27: Mix

Examples

Create a Custom Mix Task

# lib/mix/tasks/mytask.ex 
defmodule Mix.Tasks.MyTask do 
  use Mix.Task 

  @shortdoc "A simple mix task" 
  def run(_) do 
    IO.puts "YO!" 
  end 
end

Compile and run:

$ mix compile 
$ mix my_task 
"YO!"

Custom mix task with command line arguments

In a basic implementation the task module must define a run/1 function that takes a list of 
arguments. E.g. def run(args) do ... end

defmodule Mix.Tasks.Example_Task do 
  use Mix.Task 

  @shortdoc "Example_Task prints hello + its arguments" 
  def run(args) do 
    IO.puts "Hello #{args}" 
  end 
end

Compile and run:

$ mix example_task world 
"hello world"

Aliases

Elixir allows you to add aliases for your mix commands. Cool thing if you want to save yourself 
some typing.

Open mix.exs in your Elixir project.

First, add aliases/0 function to the keyword list that the project function returns. Adding () at the 

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end of the aliases function will prevent compiler from throwing a warning.

  def project do 
    [app: :my_app, 
     ... 
     aliases: aliases()] 
  end

Then, define your aliases/0 function (e.g. at the bottom of your mix.exs file).

  ... 

  defp aliases do 
    [go: "phoenix.server", 
     trident: "do deps.get, compile, go"] 
  end

You can now use $ mix go to run your Phoenix server (if you're running a Phoenix application). 
And use $ mix trident to tell mix to fetch all dependencies, compile, and run the server.

Get help on available mix tasks

To list available mix tasks use:

mix help

To get help on a specific task use mix help task e.g.:

mix help cmd

Read Mix online: https://riptutorial.com/elixir/topic/3585/mix

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Chapter 28: Modules

Remarks

Module Names

In Elixir, module names such as IO or String are just atoms under the hood and are converted to 
the form :"Elixir.ModuleName" at compile time.

iex(1)> is_atom(IO) 
true 
iex(2)> IO == :"Elixir.IO" 
true

Examples

List a module's functions or macros

The __info__/1 function takes one of the following atoms:

•
•

:functions - Returns a keyword list of public functions along with their arities
:macros - Returns a keyword list of public macros along with their arities

To list the Kernel module’s functions:

iex> Kernel.__info__ :functions 
[!=: 2, !==: 2, *: 2, +: 1, +: 2, ++: 2, -: 1, -: 2, --: 2, /: 2, <: 2, <=: 2, 
 ==: 2, ===: 2, =~: 2, >: 2, >=: 2, abs: 1, apply: 2, apply: 3, binary_part: 3, 
 bit_size: 1, byte_size: 1, div: 2, elem: 2, exit: 1, function_exported?: 3, 
 get_and_update_in: 3, get_in: 2, hd: 1, inspect: 1, inspect: 2, is_atom: 1, 
 is_binary: 1, is_bitstring: 1, is_boolean: 1, is_float: 1, is_function: 1, 
 is_function: 2, is_integer: 1, is_list: 1, is_map: 1, is_number: 1, is_pid: 1, 
 is_port: 1, is_reference: 1, is_tuple: 1, length: 1, macro_exported?: 3, 
 make_ref: 0, ...]

Replace Kernel with any module of your choosing.

Using modules

Modules have four associated keywords to make using them in other modules: alias, import, use, 
and require.

alias will register a module under a different (usually shorter) name:

defmodule MyModule do 
  # Will make this module available as `CoolFunctions` 
  alias MyOtherModule.CoolFunctions 
  # Or you can specify the name to use 

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  alias MyOtherModule.CoolFunctions, as: CoolFuncs 
end

import will make all the functions in the module available with no name in front of them:

defmodule MyModule do 
  import Enum 
  def do_things(some_list) do 
    # No need for the `Enum.` prefix 
    join(some_list, " ") 
  end 
end

use allows a module to inject code into the current module - this is typically done as part of a 
framework that creates its own functions to make your module confirm to some behaviour.

require loads macros from the module so that they can be used.

Delegating functions to another module

Use defdelegate to define functions that delegate to functions of the same name defined in another 
module:

defmodule Math do 
  defdelegate pi, to: :math 
end 

iex> Math.pi 
3.141592653589793

Read Modules online: https://riptutorial.com/elixir/topic/2721/modules

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Chapter 29: Nodes

Examples

List all visible nodes in the system

iex([email protected])> Node.list 
[:"[email protected]"]

Connecting nodes on the same machine

Start two named nodes in two terminal windows:

>iex --name [email protected] 
iex([email protected])> 
>iex --name [email protected] 
iex([email protected])>

Connect two nodes by instructing one node to connect:

iex([email protected])> Node.connect :"[email protected]" 
true

The two nodes are now connected and aware of each other:

iex([email protected])> Node.list 
[:"[email protected]"] 
iex([email protected])> Node.list 
[:"[email protected]"]

You can execute code on other nodes:

iex([email protected])> greet = fn() -> IO.puts("Hello from #{inspect(Node.self)}") end 
iex([email protected])> Node.spawn(:"[email protected]", greet) 
#PID<9007.74.0> 
Hello from :"[email protected]" 
:ok

Connecting nodes on different machines

Start a named process on one IP address:

$ iex --name [email protected] --cookie chocolate 
iex([email protected])> Node.ping :"[email protected]" 
:pong 
iex([email protected])> Node.list 
[:"[email protected]"]

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Start another named process on a different IP address:

$ iex --name [email protected] --cookie chocolate 
iex([email protected])> Node.list 
[:"[email protected]"]

Read Nodes online: https://riptutorial.com/elixir/topic/2065/nodes

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Chapter 30: Operators

Examples

The Pipe Operator

The Pipe Operator |> takes the result of an expression on the left and feeds it as the first 
parameter to a function on the right.

expression |> function

Use the Pipe Operator to chain expressions together and to visually document the flow of a series 
of functions.

Consider the following:

Oven.bake(Ingredients.Mix([:flour, :cocoa, :sugar, :milk, :eggs, :butter]), :temperature)

In the example, Oven.bake comes before Ingredients.mix, but it is executed last. Also, it may not be 
obvious that :temperature is a parameter of Oven.bake

Rewriting this example using the Pipe Operator:

[:flour, :cocoa, :sugar, :milk, :eggs, :butter] 
|> Ingredients.mix 
|> Oven.bake(:temperature)

gives the same result, but the order of execution is clearer. Furthermore, it is clear that 
:temperature is a parameter to the Oven.bake call.

Note that when using the Pipe Operator, the first parameter for each function is relocated to before 
the Pipe Operator, and so the function being called appears to have one fewer parameter. For 
instance:

Enum.each([1, 2, 3], &(&1+1)) # produces [2, 3, 4]

is the same as:

[1, 2, 3] 
|> Enum.each(&(&1+1))

Pipe operator and parentheses

Parentheses are needed to avoid ambiguity:

foo 1 |> bar 2 |> baz 3

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Should be written as:

foo(1) |> bar(2) |> baz(3)

Boolean operators

There are two kinds of boolean operators in Elixir:

•

boolean operators (they expect either true or false as their first argument)

x or y      # true if x is true, otherwise y 

x and y     # false if x is false, otherwise y 

not x       # false if x is true, otherwise true

All of booleans operators will raise ArgumentError if first argument won't be strictly boolean value, 
which means only true or false (nil is not boolean).

iex(1)> false and 1 # return false 
iex(2)> false or 1 # return 1 
iex(3)> nil and 1 # raise (ArgumentError) argument error: nil

•

relaxed boolean operators (work with any type, everything that neither false nor nil is 
considered as true)

x || y     # x if x is true, otherwise y 

x && y     # y if x is true, otherwise false 

!x         # false if x is true, otherwise true

Operator || will always return first argument if it's truthy (Elixir treats everything except nil and 
false to be true in comparisions), otherwise will return second one.

iex(1)> 1 || 3 # return 1, because 1 is truthy 
iex(2)> false || 3 # return 3 
iex(3)> 3 || false # return 3 
iex(4)> false || nil # return nil 
iex(5)> nil || false # return false

Operator && will always return second argument if it's truthy. Otherwise will return respectively to 
the arguments, false or nil.

iex(1)> 1 && 3 # return 3, first argument is truthy 
iex(2)> false && 3 # return false 
iex(3)> 3 && false # return false 
iex(4)> 3 && nil # return nil 
iex(5)> false && nil # return false 
iex(6)> nil && false # return nil

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Both && and || are short-circuit operators. They only execute the right side if the left side is not 
enough to determine the result.

Operator ! will return boolean value of negation of current term:

iex(1)> !2 # return false 
iex(2)> !false # return true 
iex(3)> !"Test" # return false 
iex(4)> !nil # return true

Simple way to get boolean value of selected term is to simply double this operator:

iex(1)> !!true # return true 
iex(2)> !!"Test" # return true 
iex(3)> !!nil # return false 
iex(4)> !!false # return false

Comparison operators

Equality:

•
•
•
•

value equality x == y (1 == 1.0 # true)
value inequality x == y (1 != 1.0 # false)
strict equality x === y (1 === 1.0 # false)
strict inequality x === y (1 !== 1.0 # true)

Comparison:

•
•
•
•

x > y
x >= y
x < y
x <= y

If types are compatible, comparison uses natural ordering. Otherwise there is general types 
comparison rule:

number < atom < reference < function < port < pid < tuple < map < list < binary

Join operators

You can join (concatenate) binaries (including strings) and lists:

iex(1)> [1, 2, 3] ++ [4, 5] 
[1, 2, 3, 4, 5] 

iex(2)> [1, 2, 3, 4, 5] -- [1, 3] 
[2, 4, 5] 

iex(3)> "qwe" <> "rty" 
"qwerty"

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'In' operator

in operator allows you to check whether a list or a range includes an item:

iex(4)> 1 in [1, 2, 3, 4] 
true 

iex(5)> 0 in (1..5) 
false

Read Operators online: https://riptutorial.com/elixir/topic/1161/operators

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Chapter 31: Optimization

Examples

Always measure first!

These are general tips that in general improve performance. If your code is slow, it is always 
important to profile it to figure out what parts are slow. Guessing is never enough. Improving the 
execution speed of something that only takes up 1% of the execution time probably isn't worth the 
effort. Look for the big time sinks.

To get somewhat accurate numbers, make sure the code you are optimizing is executed for at 
least one second when profiling. If you spend 10% of the execution time in that function, make 
sure the complete program execution takes up at least 10 seconds, and make sure you can run 
the same exact data through the code multiple times, to get repeatable numbers.

ExProf is simple to get started with.

Read Optimization online: https://riptutorial.com/elixir/topic/6062/optimization

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68

Chapter 32: Pattern matching

Examples

Pattern matching functions

#You can use pattern matching to run different 
#functions based on which parameters you pass 

#This example uses pattern matching to start, 
#run, and end a recursive function 

defmodule Counter do 
    def count_to do 
        count_to(100, 0) #No argument, init with 100 
    end 

    def count_to(counter) do 
        count_to(counter, 0) #Initialize the recursive function 
    end 

    def count_to(counter, value) when value == counter do 
        #This guard clause allows me to check my arguments against 
        #expressions. This ends the recursion when the value matches 
        #the number I am counting to. 
        :ok 
    end 

    def count_to(counter, value) do 
        #Actually do the counting 
        IO.puts value 
        count_to(counter, value + 1) 
    end 
end

Pattern matching on a map

%{username: username} = %{username: "John Doe", id: 1} 
# username == "John Doe"

%{username: username, id: 2} = %{username: "John Doe", id: 1} 
** (MatchError) no match of right hand side value: %{id: 1, username: "John Doe"}

Pattern matching on a list

You can also pattern match on Elixir Data Structures such as Lists.

Lists

Matching on a list is quite simple.

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[head | tail] = [1,2,3,4,5] 
# head == 1 
# tail == [2,3,4,5]

This works by matching the first (or more) elements in the list to the left hand side of the | (pipe) 
and the rest of the list to the right hand side variable of the |.

We can also match on specific values of a list:

[1,2 | tail] = [1,2,3,4,5] 
# tail = [3,4,5] 

[4 | tail] = [1,2,3,4,5] 
** (MatchError) no match of right hand side value: [1, 2, 3, 4, 5]

Binding multiple consecutive values on the left of the | is also allowed:

[a, b | tail] = [1,2,3,4,5] 
# a == 1 
# b == 2 
# tail = [3,4,5]

Even more complex - we can match on a specific value, and match that against a variable:

iex(11)> [a = 1 | tail] = [1,2,3,4,5] 
# a == 1

Get the sum of a list using pattern matching

defmodule Math do 
  # We start of by passing the sum/1 function a list of numbers. 
  def sum(numbers) do 
    do_sum(numbers, 0) 
  end 

  # Recurse over the list when it contains at least one element. 
  # We break the list up into two parts: 
  #   head: the first element of the list 
  #   tail: a list of all elements except the head 
  # Every time this function is executed it makes the list of numbers 
  # one element smaller until it is empty. 
  defp do_sum([head|tail], acc) do 
    do_sum(tail, head + acc) 
  end 

 # When we have reached the end of the list, return the accumulated sum 
  defp do_sum([], acc), do: acc 
end

Anonymous functions

f = fn 
  {:a, :b} -> IO.puts "Tuple {:a, :b}" 

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  [] -> IO.puts "Empty list" 
end 

f.({:a, :b}) # Tuple {:a, :b} 
f.([])       # Empty list

Tuples

{ a, b, c } = { "Hello", "World", "!" } 

IO.puts a # Hello 
IO.puts b # World 
IO.puts c # ! 

# Tuples of different size won't match: 

{ a, b, c } = { "Hello", "World" } # (MatchError) no match of right hand side value: { 
"Hello", "World" }

Reading a File

Pattern matching is useful for an operation like file reading which returns a tuple.

If the file sample.txt contains This is a sample text, then:

{ :ok, file } = File.read("sample.txt") 
# => {:ok, "This is a sample text"} 

file 
# => "This is a sample text"

Otherwise, if the file does not exist:

{ :ok, file } = File.read("sample.txt") 
# => ** (MatchError) no match of right hand side value: {:error, :enoent} 

{ :error, msg } = File.read("sample.txt") 
# => {:error, :enoent}

Pattern matching anonymous functions

fizzbuzz = fn 
  (0, 0, _) -> "FizzBuzz" 
  (0, _, _) -> "Fizz" 
  (_, 0, _) -> "Buzz" 
  (_, _, x) -> x 
end 

my_function = fn(n) -> 
  fizzbuzz.(rem(n, 3), rem(n, 5), n) 
end

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Read Pattern matching online: https://riptutorial.com/elixir/topic/1602/pattern-matching

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72

Chapter 33: Polymorphism in Elixir

Introduction

Polymorphism is the provision of a single interface to entities of different types. Basically, it allows 
different data types respond to the same function. So, the same function shapes for different data 
types to accomplish the same behavior. Elixir language has protocols to implement polymorphism 
with a clean way.

Remarks

If you want to cover all data types you can define an implementation for Any data type. Lastly, if 
you have time, check the source code of Enum and String.Char, which are good examples of 
polymorphism in core Elixir.

Examples

Polymorphism with Protocols

Let's implement a basic protocol that converts Kelvin and Fahrenheit temperatures to Celsius.

defmodule Kelvin do 
  defstruct name: "Kelvin", symbol: "K", degree: 0 
end 

defmodule Fahrenheit do 
  defstruct name: "Fahrenheit", symbol: "°F", degree: 0 
end 

defmodule Celsius do 
  defstruct name: "Celsius", symbol: "°C", degree: 0 
end 

defprotocol Temperature do 
  @doc """ 
  Convert Kelvin and Fahrenheit to Celsius degree 
  """ 
  def to_celsius(degree) 
end 

defimpl Temperature, for: Kelvin do 
  @doc """ 
  Deduct 273.15 
  """ 
  def to_celsius(kelvin) do 
    celsius_degree = kelvin.degree - 273.15 
    %Celsius{degree: celsius_degree} 
  end 
end 

defimpl Temperature, for: Fahrenheit do 

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  @doc """ 
  Deduct 32, then multiply by 5, then divide by 9 
  """ 
  def to_celsius(fahrenheit) do 
    celsius_degree = (fahrenheit.degree - 32) * 5 / 9 
    %Celsius{degree: celsius_degree} 
  end 
end

Now, we implemented our converters for the Kelvin and Fahrenheit types. Let's make some 
conversions:

iex> fahrenheit = %Fahrenheit{degree: 45} 
%Fahrenheit{degree: 45, name: "Fahrenheit", symbol: "°F"} 
iex> celsius = Temperature.to_celsius(fahrenheit) 
%Celsius{degree: 7.22, name: "Celsius", symbol: "°C"} 
iex> kelvin = %Kelvin{degree: 300} 
%Kelvin{degree: 300, name: "Kelvin", symbol: "K"} 
iex> celsius = Temperature.to_celsius(kelvin) 
%Celsius{degree: 26.85, name: "Celsius", symbol: "°C"}

Let's try to convert any other data type which has no implementation for to_celsius function:

iex> Temperature.to_celsius(%{degree: 12}) 
** (Protocol.UndefinedError) protocol Temperature not implemented for %{degree: 12} 
    iex:11: Temperature.impl_for!/1 
    iex:15: Temperature.to_celsius/1

Read Polymorphism in Elixir online: https://riptutorial.com/elixir/topic/9519/polymorphism-in-elixir

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74

Chapter 34: Processes

Examples

Spawning a Simple Process

In the following example, the greet function inside Greeter module is run in a separate process:

defmodule Greeter do 
    def greet do 
        IO.puts "Hello programmer!" 
    end 
end 

iex> spawn(Greeter, :greet, []) 
Hello 
#PID<0.122.0>

Here #PID<0.122.0> is the process identifier for the spawned process.

Sending and Receiving Messages

defmodule Processes do 
    def receiver do 
        receive do 
            {:ok, val} -> 
                IO.puts "Received Value: #{val}" 
            _ -> 
                IO.puts "Received something else" 
        end 
    end 
end

iex(1)> pid = spawn(Processes, :receiver, []) 
#PID<0.84.0> 
iex(2)> send pid, {:ok, 10} 
Received Value: 10 
{:ok, 10}

Recursion and Receive

Recursion can be used to receive multiple messages

defmodule Processes do 
    def receiver do 
        receive do 
            {:ok, val} -> 
                IO.puts "Received Value: #{val}" 
            _ -> 
                IO.puts "Received something else" 
        end 

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        receiver 
    end 
end

iex(1)> pid = spawn Processes, :receiver, [] 
#PID<0.95.0> 
iex(2)> send pid, {:ok, 10} 
Received Value: 10 
{:ok, 10} 
iex(3)> send pid, {:ok, 42} 
{:ok, 42} 
Received Value: 42 
iex(4)> send pid, :random 
:random 
Received something else

Elixir will use a tail-call recursion optimisation as long as the function call is the last thing that 
happens in the function as it is in the example.

Read Processes online: https://riptutorial.com/elixir/topic/3173/processes

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Chapter 35: Protocols

Remarks

A note on structs

Instead of sharing protocol implementation with maps, structs require their own protocol 
implementation.

Examples

Introduction

Protocols enable polymorphism in Elixir. Define protocols with defprotocol:

defprotocol Log do 
  def log(value, opts) 
end

Implement a protocol with defimpl:

require Logger 
# User and Post are custom structs 

defimpl Log, for: User do 
  def log(user, _opts) do 
    Logger.info "User: #{user.name}, #{user.age}" 
  end 
end 

defimpl Log, for: Post do 
  def log(user, _opts) do 
    Logger.info "Post: #{post.title}, #{post.category}" 
  end 
end

With the above implementations, we can do:

iex> Log.log(%User{name: "Yos", age: 23}) 
22:53:11.604 [info]  User: Yos, 23 
iex> Log.log(%Post{title: "Protocols", category: "Protocols"}) 
22:53:43.604 [info]  Post: Protocols, Protocols

Protocols let you dispatch to any data type, so long as it implements the protocol. This includes 
some built-in types such as Atom, BitString, Tuples, and others.

Read Protocols online: https://riptutorial.com/elixir/topic/3487/protocols

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Chapter 36: Sigils

Examples

Build a list of strings

iex> ~w(a b c) 
["a", "b", "c"]

Build a list of atoms

iex> ~w(a b c)a 
[:a, :b, :c]

Custom sigils

Custom sigils can be made by creating a method sigil_X where X is the letter you want to use 
(this can only be a single letter).

defmodule Sigils do 
  def sigil_j(string, options) do 
    # Split on the letter p, or do something more useful 
    String.split string, "p" 
  end 
  # Use this sigil in this module, or import it to use it elsewhere 
end

The options argument is a binary of the arguments given at the end of the sigil, for example:

~j/foople/abc # string is "foople", options are 'abc' 
# ["foo", "le"]

Read Sigils online: https://riptutorial.com/elixir/topic/2204/sigils

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78

Chapter 37: State Handling in Elixir

Examples

Managing a piece of state with an Agent

The simplest way to wrap and access a piece of state is Agent. The module allows one to spawn a 
process that keeps an arbitrary data structure and allows one to send messages to read and 
update that structure. Thanks to this the access to the structure is automatically serialized, as the 
process only handles one message at a time.

iex(1)> {:ok, pid} = Agent.start_link(fn -> :initial_value end) 
{:ok, #PID<0.62.0>} 
iex(2)> Agent.get(pid, &(&1)) 
:initial_value 
iex(3)> Agent.update(pid, fn(value) -> {value, :more_data} end) 
:ok 
iex(4)> Agent.get(pid, &(&1)) 
{:initial_value, :more_data}

Read State Handling in Elixir online: https://riptutorial.com/elixir/topic/6596/state-handling-in-elixir

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79

Chapter 38: Stream

Remarks

Streams are composable, lazy enumerables.

Due to their laziness, streams are useful when working with large (or even infinite) collections. 
When chaining many operations with Enum, intermediate lists are created, while Stream creates a 
recipe of computations that are executed at a later moment.

Examples

Chaining multiple operations

Stream is especially useful when you want to run multiple operations on a collection. This is 
because Stream is lazy and only does one iteration (whereas Enum would do multiple iterations, for 
example).

numbers = 1..100 
|> Stream.map(fn(x) -> x * 2 end) 
|> Stream.filter(fn(x) -> rem(x, 2) == 0 end) 
|> Stream.take_every(3) 
|> Enum.to_list 

[2, 8, 14, 20, 26, 32, 38, 44, 50, 56, 62, 68, 74, 80, 86, 92, 98, 104, 110, 
 116, 122, 128, 134, 140, 146, 152, 158, 164, 170, 176, 182, 188, 194, 200]

Here, we chained 3 operations (map, filter and take_every), but the final iteration was only done 
after Enum.to_list was called.

What Stream does internally, is that it waits until actual evaluation is required. Before that, it creates 
a list of all the functions, but once evaluation is needed, it does goes through the collection once, 
running all the functions on every item. This makes it more efficient than Enum, which in this case 
would do 3 iterations, for example.

Read Stream online: https://riptutorial.com/elixir/topic/2553/stream

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Chapter 39: Strings

Remarks

A String in Elixir is a UTF-8 encoded binary.

Examples

Convert to string

Use Kernel.inspect to convert anything to string.

iex> Kernel.inspect(1) 
"1" 
iex> Kernel.inspect(4.2) 
"4.2" 
iex> Kernel.inspect %{pi: 3.14, name: "Yos"} 
"%{pi: 3.14, name: \"Yos\"}"

Get a substring

iex> my_string = "Lorem ipsum dolor sit amet, consectetur adipiscing elit." 
iex> String.slice my_string, 6..10 
"ipsum"

Split a string

iex> String.split("Elixir, Antidote, Panacea", ",") 
["Elixir", "Antidote", "Panacea"]

String Interpolation

iex(1)> name = "John" 
"John" 
iex(2)> greeting = "Hello, #{name}" 
"Hello, John" 
iex(3)> num = 15 
15 
iex(4)> results = "#{num} item(s) found." 
"15 item(s) found."

Check if String contains Substring

iex(1)> String.contains? "elixir of life", "of" 
true 
iex(2)> String.contains? "elixir of life", ["life", "death"] 
true 

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81

iex(3)> String.contains? "elixir of life", ["venus", "mercury"] 
false

Join Strings

You can concatenate strings in Elixir using the <> operator:

"Hello" <> "World"                           # => "HelloWorld"

For a List of Strings, you can use Enum.join/2:

Enum.join(["A", "few", "words"], " ")        # => "A few words"

Read Strings online: https://riptutorial.com/elixir/topic/2618/strings

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82

Chapter 40: Task

Syntax

•
•

Task.async(fun)
Task.await(task)

Parameters

Parameter Details

fun

task

The function that should be executed in a separate process.

The task returned by Task.async.

Examples

Doing work in the background

task = Task.async(fn -> expensive_computation end) 
do_something_else 
result = Task.await(task)

Parallel processing

crawled_site = ["http://www.google.com", "http://www.stackoverflow.com"] 
|> Enum.map(fn site -> Task.async(fn -> crawl(site) end) end) 
|> Enum.map(&Task.await/1)

Read Task online: https://riptutorial.com/elixir/topic/7588/task

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83

Chapter 41: Tips and Tricks

Introduction

Elixir Advanced tips and tricks which save our time while coding.

Examples

Creating Custom Sigils and Documenting

Each x sigil call respective sigil_x definition

Defining Custom Sigils

defmodule MySigils do 
  #returns the downcasing string if option l is given then returns the list of downcase 
letters 
  def sigil_l(string,[]), do: String.Casing.downcase(string) 
  def sigil_l(string,[?l]), do: String.Casing.downcase(string) |> String.graphemes 

  #returns the upcasing string if option l is given then returns the list of downcase letters 
  def sigil_u(string,[]), do: String.Casing.upcase(string) 
  def sigil_u(string,[?l]), do: String.Casing.upcase(string) |> String.graphemes 
end

Multiple [ OR ]

This is just the other way of writing Multiple OR conditions. This is not the recommended approach 
because in regular approach when the condition evaluates to true, it stops executing the remaining 
conditions which save the time of evaluation, unlike this approach which evaluates all conditions 
first in the list. This is just bad but good for discoveries.

# Regular Approach 
find = fn(x) when x>10 or x<5 or x==7 -> x end 

# Our Hack 
hell = fn(x) when true in [x>10,x<5,x==7] -> x end

iex Custom Configuration - iex Decoration

Copy the content into a file and save the file as .iex.exs in your ~ home directory and see the 
magic. You can also download the file HERE

# IEx.configure colors: [enabled: true] 
# IEx.configure colors: [ eval_result: [ :cyan, :bright ] ] 
IO.puts IO.ANSI.red_background() <> IO.ANSI.white() <> " ❄❄❄ Good Luck with Elixir ❄❄❄ " <> IO.ANSI.reset 
Application.put_env(:elixir, :ansi_enabled, true) 
IEx.configure( 

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84

 
 
 colors: [ 
   eval_result: [:green, :bright] , 
   eval_error: [[:red,:bright,"Bug Bug ..!!"]], 
   eval_info: [:yellow, :bright ], 
 ], 
 default_prompt: [ 
   "\e[G",    # ANSI CHA, move cursor to column 1 
    :white, 
    "I", 
    :red, 
    "❤" ,       # plain string 
    :green, 
    "%prefix",:white,"|", 
     :blue, 
     "%counter", 
     :white, 
     "|", 
    :red, 
    "▶" ,         # plain string 
    :white, 
    "▶▶"  ,       # plain string 
      # ❤ ❤-»" ,  # plain string 
    :reset 
  ] |> IO.ANSI.format |> IO.chardata_to_string 

)

Read Tips and Tricks online: https://riptutorial.com/elixir/topic/10623/tips-and-tricks

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85

 
Credits

S. 
No

Chapters

Contributors

Getting started with 
Elixir Language

alejosocorro, Andrey Chernykh, Ben Bals, Community, cwc, 
Delameko, Douglas Correa, helcim, I Am Batman, JAlberto, 
koolkat, leifg, MattW., rap-2-h, Simone Carletti, Stephan 
Rodemeier, Vinicius Quaiato, Yedhu Krishnan, Zimm i48

Basic .gitignore for 
elixir program

Yos Riady

basic use of guard 
clauses

alxndr

BEAM

Yos Riady

Behaviours

Yos Riady

Better debugging 
with IO.inspect and 
labels

leifg

Built-in types

Conditionals

Andrey Chernykh, Arithmeticbird, Oskar, TreyE, Vinicius 
Quaiato

Andrey Chernykh, evuez, javanut13, Musfiqur Rahman, Paweł 
Obrok

Constants

ibgib

1

2

3

4

5

6

7

8

9

10 Data Structures

Sam Mercier, Simone Carletti, Stephan Rodemeier, Yos Riady

11 Debugging Tips

javanut13, Paweł Obrok, Pfitz, Philippe-Arnaud de MANGOU, 
sbs

12 Doctests

aholt, milmazz, Philippe-Arnaud de MANGOU, Yos Riady

13 Ecto

14 Erlang

15 ExDoc

16 ExUnit

fgutierr, Philippe-Arnaud de MANGOU, toraritte

4444, Yos Riady

milmazz, Yos Riady

Yos Riady

17

Functional 

Dinesh Balasubramanian

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86

programming in Elixir

18

Functions

Andrey Chernykh, cwc, Dair, Eiji, Filip Haglund, PatNowak, 
rainteller, Simone Carletti, Stephan Rodemeier, Yedhu Krishnan
, Yos Riady

19

20

Getting help in IEx 
console

helcim

IEx Console Tips & 
Tricks

alxndr, Cifer, fahrradflucht, legoscia, mudasobwa, muttonlamb, 
PatNowak, Paweł Obrok, sbs, Sheharyar, Simone Carletti, 
Stephan Rodemeier, Uniaika, Vincent, Yos Riady

21

Installation

cwc, Douglas Correa, Eiji, JAlberto, MattW.

22

Join Strings

Agung Santoso

23

Lists

Ben Bals, Candy Gumdrop, emoragaf, PatNowak, Sheharyar, 
Yos Riady

24

Maps and Keyword 
Lists

Sam Mercier, Simone Carletti, Yos Riady

25 Metaprogramming

4444, Paweł Obrok

26 Mix

4444, helcim, rainteller, Slava.K, Yos Riady

27 Modules

Alex G, javanut13, Yos Riady

28 Nodes

Yos Riady

29 Operators

alxndr, Andrey Chernykh, Dair, Gazler, Mitkins, nirev, PatNowak

30 Optimization

Filip Haglund, legoscia

31 Pattern matching

Alex Anderson, Dair, Danny Rosenblatt, evuez, Gabriel C, gmile
, Harrison Lucas, javanut13, Oskar, PatNowak, theIV, Thomas, 
Yedhu Krishnan

32

Polymorphism in 
Elixir

mustafaturan

33 Processes

Alex G, Yedhu Krishnan

34 Protocols

Yos Riady

35 Sigils

javanut13, Yos Riady

36

State Handling in 
Elixir

Paweł Obrok

https://riptutorial.com/

87

37 Stream

Oskar

38 Strings

Alex G, Sheharyar, Yos Riady

39

Task

mario

40

Tips and Tricks

Ankanna

https://riptutorial.com/

88