basic types

Hello world

# hello.exs
defmodule Greeter do
  def greet(name) do
    message = "Hello, " <> name <> "!"
    IO.puts message
  end
end

Greeter.greet("world")

elixir hello.exs
# Hello, world!

Variables

age = 23

Maps

user = %{
  name: "John",
  city: "Melbourne"
}

IO.puts "Hello, " <> user.name

Lists

users = [ "Tom", "Dick", "Harry" ]

Enum.map(user, fn user ->
  IO.puts "Hello " <> user
end)

Piping

source
|> transform(:hello)
|> print()

# Same as:
print(transform(source, :hello))

These two are equivalent.

Pattern matching

user = %{name: "Tom", age: 23}
%{name: username} = user

This sets username to "Tom".

Pattern matching in functions

def greet(%{name: username}) do
  IO.puts "Hello, " <> username
end

user = %{name: "Tom", age: 23}

Pattern matching works in function parameters too.

Control flow

If

if false do
  "This will never be seen"
else
  "This will"
end

Cond

cond do
  1 + 1 == 3 ->
    "I will never be seen"
  2 * 5 == 12 ->
    "Me neither"
  _ ->
    "But I will (this is essentially an else)"
end

Errors

try do
  throw(:hello)
catch
  message -> "Got #{message}."
after
  IO.puts("I'm the after clause.")
end

Types

Primitives

Sample	Type
`nil`	Nil/null
`true` / `false`	Boolean
---	---
`?a`	Integer (ASCII)
`23`	Integer
`3.14`	Float
---	---
`'hello'`	Char list
`<<2, 3>>`	Binary
`"hello"`	Binary string
`:hello`	Atom
---	---
`[a, b]`	List
`{a, b}`	Tuple
---	---
`%{a: "hello"}`	Map
`%MyStruct{a: "hello"}`	Struct
`fn -> ... end`	Function

Type checks

is_atom/1
is_bitstring/1
is_boolean/1
is_function/1
is_function/2
is_integer/1
is_float/1

is_binary/1
is_list/1
is_map/1
is_tuple/1

is_nil/1
is_number/1
is_pid/1
is_port/1
is_reference/1

Operators

left != right   # equal
left !== right  # match
left ++ right   # concat lists
left <> right   # concat string/binary
left =~ right   # regexp

Modules

Importing

require Redux   # compiles a module
import Redux    # compiles, and you can use without the `Redux.` prefix

use Redux       # compiles, and runs Redux.__using__/1
use Redux, async: true

import Redux, only: [duplicate: 2]
import Redux, only: :functions
import Redux, only: :macros

import Foo.{Bar, Baz}

Aliases

alias Foo.Bar, as: Bar
alias Foo.Bar   # same as above

alias Foo.{Bar, Baz}

String

Functions

import String

str = "hello"
str |> length()        # → 5
str |> codepoints()    # → ["h", "e", "l", "l", "o"]
str |> slice(2..-1)    # → "llo"
str |> split(" ")      # → ["hello"]
str |> capitalize()    # → "Hello"
str |> match(regex)

Inspecting objects

inspect(object, opts \\ [])

value |> IO.inspect()

Numbers

Operations

abs(n)
round(n)
rem(a, b)   # remainder (modulo)
div(a, b)   # integer division

Float

import Float

n = 10.3

n |> ceil()            # → 11.0
n |> ceil(2)           # → 11.30
n |> to_string()       # → "1.030000+e01"
n |> to_string([decimals: 2, compact: true])

Float.parse("34")  # → { 34.0, "" }

Integer

import Integer

n = 12

n |> digits()         # → [1, 2]
n |> to_char_list()   # → '12'
n |> to_string()      # → "12"
n |> is_even()
n |> is_odd()

# Different base:
n |> digits(2)        # → [1, 1, 0, 0]
n |> to_char_list(2)  # → '1100'
n |> to_string(2)     # → "1100"

parse("12")           # → {12, ""}
undigits([1, 2])      # → 12

Type casting

Float.parse("34.1")    # → {34.1, ""}
Integer.parse("34")    # → {34, ""}

Float.to_string(34.1)  # → "3.4100e+01"
Float.to_string(34.1, [decimals: 2, compact: true])  # → "34.1"

Map

Defining

m = %{name: "hi"}       # atom keys (:name)
m = %{"name" => "hi"}   # string keys ("name")

Updating

import Map

m = %{m | name: "yo"}  # key must exist

m |> put(:id, 2)      # → %{id: 2, name: "hi"}
m |> put_new(:id, 2)  # only if `id` doesn't exist (`||=`)

m |> put(:b, "Banana")
m |> merge(%{b: "Banana"})
m |> update(:a, &(&1 + 1))
m |> update(:a, fun a -> a + 1 end)

m |> get_and_update(:a, &(&1 || "default"))
# → {old, new}

Deleting

m |> delete(:name)  # → %{}
m |> pop(:name)     # → {"John", %{}}

Reading

m |> get(:id)       # → 1
m |> keys()         # → [:id, :name]
m |> values()       # → [1, "hi"]

m |> to_list()      # → [id: 1, name: "hi"]
                    # → [{:id, 1}, {:name, "hi"}]

Deep

put_in(map, [:b, :c], "Banana")
put_in(map[:b][:c], "Banana")    # via macros

get_and_update_in(users, ["john", :age], &{&1, &1 + 1})

Constructing from lists

Map.new([{:b, 1}, {:a, 2}])
Map.new([a: 1, b: 2])
Map.new([:a, :b], fn x -> {x, x} end)  # → %{a: :a, b: :b}

List

import List

l = [ 1, 2, 3, 4 ]

l = l ++ [5]         # push (append)
l = [ 0 | list ]     # unshift (prepend)

l |> first()
l |> last()

l |> flatten()
l |> flatten(tail)

Also see Enum.

Enum

Usage

import Enum

list = [:a, :b, :c]

list |> at(0)         # → :a
list |> count()       # → 3
list |> empty?()      # → false
list |> any?()        # → true

list |> concat([:d])  # → [:d]

Map/reduce

list |> reduce(fn)
list |> reduce(acc, fn)
list |> map(fn)
list |> reject(fn)
list |> any?(fn)
list |> empty?(fn)

[1, 2, 3, 4]
|> Enum.reduce(0, fn(x, acc) -> x + acc end)

Tuple

Tuples

import Tuple

t = { :a, :b }

t |> elem(1)    # like tuple[1]
t |> put_elem(index, value)
t |> tuple_size()

Keyword lists

list = [{ :name, "John" }, { :age, 15 }]
list[:name]

# For string-keyed keyword lists
list = [{"size", 2}, {"type", "shoe"}]
List.keyfind(list, "size", 0)  # → {"size", 2}

Functions

Lambdas

square = fn n -> n*n end
square.(20)

& syntax

square = &(&1 * &1)
square.(20)

square = &Math.square/1

Running

fun.(args)
apply(fun, args)
apply(module, fun, args)

Function heads

def join(a, b \\ nil)
def join(a, b) when is_nil(b) do: a
def join(a, b) do: a <> b

Structs

defmodule User do
  defstruct name: "", age: nil
end

%User{name: "John", age: 20}

%User{}.struct  # → User

See: Structs

Protocols

Defining protocols

defprotocol Blank do
  @doc "Returns true if data is considered blank/empty"
  def blank?(data)
end

defimpl Blank, for: List do
  def blank?([]), do: true
  def blank?(_), do: false
end

Blank.blank?([])  # → true

Any

defimpl Blank, for: Any do ... end

defmodule User do
  @derive Blank     # Falls back to Any
  defstruct name: ""
end

Examples

Enumerable and Enum.map()
Inspect and inspect()

Comprehensions

For

for n <- [1, 2, 3, 4], do: n * n
for n <- 1..4, do: n * n

for {key, val} <- %{a: 10, b: 20}, do: val
# → [10, 20]

for {key, val} <- %{a: 10, b: 20}, into: %{}, do: {key, val*val}

Conditions

for n <- 1..10, rem(n, 2) == 0, do: n
# → [2, 4, 6, 8, 10]

Complex

for dir <- dirs,
    file <- File.ls!(dir),          # nested comprehension
    path = Path.join(dir, file),    # invoked
    File.regular?(path) do          # condition
  IO.puts(file)
end

Misc

Metaprogramming

__MODULE__
__MODULE__.__info__

@after_compile __MODULE__
def __before_compile__(env)
def __after_compile__(env, _bytecode)
def __using__(opts)    # invoked on `use`

@on_definition {__MODULE__, :on_def}
def on_def(_env, kind, name, args, guards, body)

@on_load :load_check
def load_check

Regexp

exp = ~r/hello/
exp = ~r/hello/i
"hello world" =~ exp

Sigils

~r/regexp/
~w(list of strings)
~s[strings with #{interpolation} and \x20 escape codes]
~S[no interpolation and no escapes]
~c(char list)

Allowed chars: / | " ' ( [ { < """. See: Sigils {{ ::card-item:: }}

Type specs

@spec round(number) :: integer

@type number_with_remark :: {number, String.t}
@spec add(number, number) :: number_with_remark

Useful for dialyzer. See: Typespecs {{ ::card-item:: }}

Behaviours

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

defmodule JSONParser do
  @behaviour Parser

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

See: Module

Files

elixir.md

Latest commit

History

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File metadata and controls

basic types

Hello world

Variables

Maps

Lists

Piping

Pattern matching

Pattern matching in functions

Control flow

If

Cond

Errors

Types

Primitives

Type checks

Operators

Modules

Importing

Aliases

String

Functions

Inspecting objects

Numbers

Operations

Float

Integer

Type casting

Map

Defining

Updating

Deleting

Reading

Deep

Constructing from lists

List

Enum

Usage

Map/reduce

Tuple

Tuples

Keyword lists

Functions

Lambdas

& syntax

Running

Function heads

Structs

Structs

Protocols

Defining protocols

Any

Examples

Comprehensions

For

Conditions

Complex

Misc

Metaprogramming

Regexp

Sigils

Type specs

Behaviours