Elixircheatsheet

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

BASH
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elixir hello.exs
# Hello, world!

ELIXIR
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age = 23

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

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

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

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

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

ELIXIR
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print(transform(source, :hello))

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

ELIXIR
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def greet(%{name: username}) do
  IO.puts "Hello, " <> username
end
user = %{name: "Tom", age: 23}

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

ELIXIR
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case {1, 2, 3} do
  {4, 5, 6} ->
    "This clause won't match"
  {1, x, 3} ->
    "This will match and bind x to 2"
  _ ->
   "This will match any value"
end

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

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

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

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

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

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

ELIXIR
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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}

ELIXIR
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alias Foo.Bar, as: Bar
alias Foo.Bar   # same as above
alias Foo.{Bar, Baz}

ELIXIR
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import String

ELIXIR
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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)

ELIXIR
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inspect(object, opts \\ [])

ELIXIR
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value |> IO.inspect()

ELIXIR
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value |> IO.inspect(label: "value")

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

ELIXIR
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import Float

ELIXIR
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n = 10.3

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

ELIXIR
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Float.parse("34")  # → { 34.0, "" }

ELIXIR
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import Integer

ELIXIR
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n = 12

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

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

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

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

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

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

ELIXIR
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import Map

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

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

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

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

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

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

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

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

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

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

ELIXIR
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import Enum

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

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

ELIXIR
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list |> concat([:d])  # → [:a, :b, :c, :d]

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

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

ELIXIR
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import Tuple

ELIXIR
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t = { :a, :b }

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

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

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

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

ELIXIR
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square = &(&1 * &1)
square.(20)
square = &Math.square/1

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

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

ELIXIR
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defmodule User do
  defstruct name: "", age: nil
end
%User{name: "John", age: 20}
%User{}.struct  # → User

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

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

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

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

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

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

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

ELIXIR
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for dir <- dirs,
    file <- File.ls!(dir),          # 嵌套
    path = Path.join(dir, file),    # 调用
    File.regular?(path) do          # 条件判断
  IO.puts(file)
end

ELIXIR
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__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

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

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

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

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

ELIXIR
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defmodule JSONParser do
  @behaviour Parser
  def parse(str), do: # ... parse JSON
  def extensions, do: ["json"]
end