Instalamos ASDF

brew install asdf

Instalamos Erlang y Elixir

asdf install erlang 22.2.2
asdf install elixir 1.10
iex

En caso de que el observer no ande, chequear troubleshooting.

Teoría:

  • Datos, Estructuras de datos, Pattern matching.
  • Idiomas propios: If, do-end, Cond, Case.
  • Modulos, Funciones nombradas y guardas.
  • Funciones anónimas y operador de captura.
  • Recursión.

Basic Data Types

iex> 1          # integer
iex> 1.0        # float
iex> true       # boolean
iex> :atom      # atom / symbol
iex> "elixir"   # string

Tuple

iex> tuple = {1, :two, "three"}  
iex> elem(tuple, 0)
1
iex> elem(tuple, 2) 
"three"
iex> put_elem(tuple, 0, 'uno')
{'uno', :two, "three"}
iex> tuple_size(tuple)
3

Tuple module

Tuple.append(tuple, value)
# Inserts an element at the end of a tuple.
Tuple.delete_at(tuple, index)
# Removes an element from a tuple.
Tuple.duplicate(data, size)
# Creates a new tuple.
Tuple.insert_at(tuple, index, value)
# Inserts an element into a tuple.
Tuple.to_list(tuple)
# Converts a tuple to a list.

Doc: Tuple

List

iex> [1, "two", 3, :four]
[1, "two", 3, :four]
iex> [1, 2, 3] ++ [4, 5, 6]
[1, 2, 3, 4, 5, 6]
iex> [1, true, 2, false, 3, true] -- [true, false]
[1, 2, 3, true]
iex> [1, "two", :three, 4] ++ ["more numbers"]
[1, "two", :three, 4, "more numbers"]
iex> hd([1, 2, 3])
1
iex> tl([1, 2, 3])
[2,3]
iex> 2 in [1,2,3]
true

iex> [0 | [1, "two", 3, :four]]
[0, 1, "two", 3, :four]
iex> [1 | [2 | [3 | []]]]
[1, 2, 3]

iex> list = [1, 2, 3]
iex> [0 | list] # fast
[0, 1, 2, 3]
iex> list ++ [4] # slow
[1, 2, 3, 4]

List module

List.delete(list, element)
# Deletes the given element from the list.
# Returns a new list without the element.
List.delete_at(list, index)
# Produces a new list by removing the value at the specified index.
List.first(list)
# Returns the first element in list or nil if list is empty.
List.flatten(list)
# Flattens the given list of nested lists.

Doc: List

Keyword

iex> [{:first_number, 1}, {:second_number, 2}]
[first_number: 1, second_number: 2]

iex> [first_number: 1, second_number: 2]
[first_number: 1, second_number: 2]

Keyword module

Keyword.fetch(keywords, key)
# Fetches the value for a specific key and returns it in a tuple.
Keyword.fetch!(keywords, key)
# Fetches the value for specific key.
Keyword.keys(keywords)
# Returns all keys from the keyword list.
Keyword.values(keywords)
# Returns all values from the keyword list.
Keyword.split(keywords, keys)
# Takes all entries corresponding to the given keys and
# extracts them into a separate keyword list.
Keyword.take(keywords, keys)
# Takes all entries corresponding to the given keys and
# returns them in a new keyword list.

Doc: Keyword

Map

iex> %{"one" => :two, 3 => "four"}
%{3 => "four", "one" => :two}
iex> map = %{a: 1, b: 2}
iex> map[:b]
2
iex> map["non_existing_key"]
nil
iex> map.a
1
iex> map.non_existing_key
** (KeyError) key :non_existing_key not found in: %{a: 1, b: 2}

Map module

Map.drop(map, keys)
# Drops the given keys from map.
Map.equal?(map1, map2)
# Checks if two maps are equal.
Map.from_struct(struct)
# Converts a struct to map.
Map.fet(map, key, default \\ nil)
# Gets the value for a specific key in map.
Map.has_key?(map, key)
# Returns whether the given key exists in the given map.

Doc: Map

MapSet module

iex> my_set = MapSet.new([1, 2, 3, 4, 5])
iex> MapSet.put(my_set, 6)
MapSet<[1, 2, 3, 4, 5, 6]>
iex> MapSet.delete(my_set, 6)
MapSet<[1, 2, 3, 4, 5]>

MapSet.difference(map_set1, map_set2)
# Returns a set that is map_set1 without the members of map_set2.
MapSet.disjoint?(map_set1, map_set2)
# Checks if map_set1 and map_set2 have no members in common.
MapSet.intersection(map_set, map_set)
# Returns a set containing only members that map_set1 and 
# map_set2 have in common.
MapSet.subset?(map_set1, map_set2)
# Checks if map_set1's members are all contained in map_set2.
MapSet.union(map_set1, map_set2)
# Returns a set containing all members of map_set1 and map_set2.

Doc: MapSet

Struct

iex> defmodule User do
...>   defstruct name: "John", age: 27
...> end

iex> %User{}
%User{age: 27, name: "John"}
iex> %User{name: "Jane"}
%User{age: 27, name: "Jane"}

iex> %User{oops: :field}
** (KeyError) key :oops not found in: %User{age: 27, name: "John"}

Enumerable and Enum

The protocol Enumerable is implemented by Range, List and Map. So many function to work with these are found in the Enum module.

Pattern Matching

Match Operator

Símbolo “=”

iex(1)> x = 2
2
iex(2)> 2 = x
2
iex(3)> 1 = x
** (MatchError) no match of right hand side value: 2
    (stdlib) erl_eval.erl:453: :erl_eval.expr/5
    (iex) lib/iex/evaluator.ex:257: IEx.Evaluator.handle_eval/5
    (iex) lib/iex/evaluator.ex:237: IEx.Evaluator.do_eval/3
    (iex) lib/iex/evaluator.ex:215: IEx.Evaluator.eval/3
    (iex) lib/iex/evaluator.ex:103: IEx.Evaluator.loop/1
    (iex) lib/iex/evaluator.ex:27: IEx.Evaluator.init/4

With tuples

iex> {a, b, c} = {:hello, "world", 42}
{:hello, "world", 42}
iex> a
:hello
iex> b
"world"

iex> {:ok, result} = {:ok, 13}
{:ok, 13}
iex> result
13

With Lists

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

With Structs

iex> %User{name: "Fede", age: age} = %User{name: "Fede", age: 30}
%User{age: 30, name: "Fede"}

iex> %{name: "Fede", age: age} = %User{name: "Fede", age: 30}
%User{age: 30, name: "Fede"}

iex> %User{name: "Fede", age: age} = %{name: "Fede", age: 30}
** (MatchError) no match of right hand side value: %{age: 30, name: "Fede"}
    (stdlib) erl_eval.erl:453: :erl_eval.expr/5
    (iex) lib/iex/evaluator.ex:257: IEx.Evaluator.handle_eval/5
    (iex) lib/iex/evaluator.ex:237: IEx.Evaluator.do_eval/3
    (iex) lib/iex/evaluator.ex:215: IEx.Evaluator.eval/3
    (iex) lib/iex/evaluator.ex:103: IEx.Evaluator.loop/1
    (iex) lib/iex/evaluator.ex:27: IEx.Evaluator.init/4

Pin Operator

iex> x = 1
1
iex> ^x = 2
** (MatchError) no match of right hand side value: 2
iex> {y, ^x} = {2, 1}
{2, 1}
iex> y
2
iex> {y, ^x} = {2, 2}
** (MatchError) no match of right hand side value: {2, 2}

Underscore

iex> [head | _] = [1, 2, 3]
[1, 2, 3]
iex> head
1

iex> _
** (CompileError) iex:1: invalid use of _. "_" represents a
  value to be ignored in a pattern and cannot be used in expressions

Real Example

response = HTTP.patch(url, body, headers, [])
case response do
  {:ok, %{status_code: 200, body: body}} ->
    body
  {:ok, %{status_code: 404} = resp} ->
    "Error: #{resp.status_code} Not found!"
  {:error, %{reason: reason}} ->
    "Error: #{reason}"
end

If

if x > 0 do
  "Positivo"
else
  "No positivo"
end

Cond

cond do
  x == 0 -> "Cero"
  x > 0  -> "Positivo"
  true   -> "Negativo"
end

Case

case workday do
  0 -> "Lunes"
  1 -> "Martes"
  2 -> "Miércoles"
  3 -> "Jueves"
  4 -> "Viernes"
  _ -> "#{workday} es inválido"
end

Modulos y funciones

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

Multiples definiciones

defmodule Math do
  def zero?(0) do
    true
  end
  
  def zero?(x) do
    false
  end
end

Con guardas

defmodule Math do
  def zero?(0) do
    true
  end
  
  def zero?(x) when is_integer(x) do
    false
  end
end

Funciones anonimas

inc = fn (a) -> a + 1 end
inc.(2) #=> 3
Enum.map([1,2,3], inc)
#=> [2,3,4]

Operador de captura

defmodule Math do
  def inc(x), do: x + 1
end

Enum.map([1,2,3], &Math.inc/1)
#=> [2,3,4]

Elixir Flashcards

  • Kernel I
  • Fundamentals I
  • Fundamentals II

Instalar Phoenix

Asumimos que ya está instalado node.js y postgresql. Pero si no están, nos tomamos el tiempo de instalarlos.

mix local.hex
mix archive.install hex phx_new 1.4.12

Configurar nueva aplicación:

mix phx.new yo
cd yo

Configuramos nuestro acceso a base de datos en config/dev.exs

mix ecto.create
mix phx.server

Vamos a 127.0.0.1:4000

Subir a Heroku

Creamos la aplicación en Heroku usando el Elixir buildpack:

heroku create --buildpack hashnuke/elixir

Creamos archivo elixir_buildpack.config y agregamos:

# Elixir version
elixir_version=1.10.0

# Erlang version
erlang_version=21.2.5

Agregamos Phoenix build pack:

heroku buildpacks:add https://github.com/gjaldon/heroku-buildpack-phoenix-static.git

En config/prod.exs reemplazamos:

url: [host: "example.com", port: 80],

Por:

http: [port: {:system, "PORT"}],
url: [scheme: "https", host: "mysterious-meadow-6277.herokuapp.com", port: 443],
force_ssl: [rewrite_on: [:x_forwarded_proto]],

Descomentamos de config/prod.secret.exs la linea:

ssl: true

En endpoint.ex reemplazamos:

websocket: true,

Por:

websocket: [timeout: 45_000],

Agregamos add-on de postresql para nuestra aplicación heroku:

heroku addons:create heroku-postgresql:hobby-dev

Seteamos el Pool size en Heroku:

heroku config:set POOL_SIZE=18

Generamos secret key:

mix phx.gen.secret

Y la subimos a Heroku:

heroku config:set SECRET_KEY_BASE=“XXXX”

Hacemos push a Heroku:

git add .
git commit -m "Use production config from Heroku ENV variables and decrease socket timeout"
git push heroku master

Si falla, probar lo siguiente.

  1. Agregamos archivo Procfile con: 
    web: elixir --sname server -S mix phx.server
  2. Agregamos phoenix_static_buildpack.config con: 
    node_version=8.9.0
assets_path=assets
phoenix_ex=phx

Nuestra Aplicación:

  • Mostrar muy por arriba estructura de aplicación (Mix.exs, routes, controller, template)

Corremos generador de Posts

mix phx.gen.html Blog Post posts title:string body:string
  • Entrar a la migración, mostrarla y mix ecto.migrate
  • Agregar al router la line resources …
  • Mostrar la aplicacion en localhost:4000/posts
  • Ruta, controlador, Vistas