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O Essencial da Programação Funcional em Elixir

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3 conceitos essenciais

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⏹ Funções ⏹ Código declarativo ⏹ Imutabilidade

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Me

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@ulissesalmeida

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@ulissesalmeida

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Não estamos contratando !

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Banco de Talentos Elixir / Ruby

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http:// careers.plataformatec.co m.br/

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20% de desconto Elixir Brasil

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Agora chega vamos voltar pra talk XD

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Por que se preocupar com paralelismo?

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Múltiplos núcleos ! Paralelismo

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Your Erlang program should just run N times faster on an N core processor https://pragprog.com/articles/erlang

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Básico Programa que não roda em paralelo Roda 0 vezes mais rápido com 2 ou mais cores

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50% paralelizável 2 vezes mais rápido

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75% paralelizável ~3 vezes mais rápido

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90% paralelizável ~6 vezes mais rápido

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95% paralelizável ~9 vezes mais rápido

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Quanto mais partes do programa em paralelo melhor!?

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O código sozinho não roda em paralelo

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!

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Threads

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Precisa reduzir a complexidade

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Programação Funcional ❤ Paralelismo

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⏹ Funções ⏹ Código declarativo ⏹ Imutabilidade

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Funções puras

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Escopo { Argumento } Argumento => Resultado Valores imutáveis

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add2 = fn (n) -> n + 2 end add2.(2) # => 4

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Valores sempre são explícitos

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Ruby

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class MySet attr_reader :items def initialize @items = [] end def push(item) items.push(item) unless items.include?(item) end end

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set = MySet.new set.push("apple") new_set = MySet.new new_set.push("pie") set.push("apple") # => ["apple"] new_set.push("apple") # => ["pie", "apple"]

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class Order attr_reader :user, :products, :logger, :mailer, :payment, :source #... end

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Elixir

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defmodule MySet do defstruct items: [] def push(set = %{items: items}, item) do if Enum.member?(items, item) do set else %{set | items: items ++ [item]} end end end

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set = %MySet{} set = MySet.push(set, "apple") new_set = %MySet{} new_set = MySet.push(new_set, "pie") IO.inspect MySet.push(set, "apple") # => ["apple"] IO.inspect MySet.push(new_set, "apple") # => ["pie", "apple"]

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Funções como valores

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Enum.map( ["dogs", "cats", "flowers"], &String.upcase/1 ) # => ["DOGS", "CATS", "FLOWERS"]

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Transformação de valores

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capitalize_words("the dark tower") # => "The Dark Tower"

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def capitalize_words(title) do join_with_whitespace( capitalize_all( String.split(title) ) ) end

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def capitalize_words(title) do title |> String.split |> capitalize_all |> join_with_whitespace end

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✅ Funções ⏹ Código declarativo ⏹ Imutabilidade

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Código imperativo Foco no como

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Javascript

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function capitalizeAll(list) { var newList = []; for (var i = 0; i < list.length; i++) { newList.push(capitalize(list[i])); } return newList; } function capitalize(string) { return string.charAt(0).toUpperCase() + string.slice(1); }

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var list = ["dogs", "hot dogs", "bananas"]; capitalizeAll(list); // => ["Dogs", "Hot dogs", "Bananas"]

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Código declarativo Foco no o quê

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Elixir

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defmodule StringList do def capitalize_all([]), do: [] def capitalize_all([first | rest]) do [String.capitalize(first) | capitalize_all(rest)] end end

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list = ["dogs", "hot dogs", "bananas"] Enum.map(list, &String.capitalize/1) # => ["Dogs", "Hot Dogs", "Bananas"]

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Javascript

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list = ["dogs", "hot dogs", "bananas"] list.map((i) => i.toUpperCase()); // => ["DOGS", "HOT DOGS", "BANANAS"]

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Ruby

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list = ["dogs", "hot dogs", "bananas"] list.map(&:upcase) # => ["DOGS", "HOT DOGS", "BANANAS"]

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✅ Funções ✅ Código declarativo ⏹ Imutabilidade

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Ruby

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list = [1, 2, 3, 4] list.pop puts list.inspect # => [1, 2, 3] list.push(1) puts list.inspect # => [1, 2, 3, 1]

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Account = Struct.new(:amount) do def deposit(value) new_amount = amount + value sleep(1) self.amount = new_amount end def withdraw(value) new_amount = amount - value sleep(1) self.amount = new_amount end end

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ilisses = Account.new(100) ilisses.deposit(20) ilisses.withdraw(20) ilisses.amount # 100

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ilisses = Account.new(100) Thread.new { ilisses.deposit(20) } Thread.new { ilisses.withdraw(20) }

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ilisses = Account.new(100) 5.times.map { Thread.new { ilisses.deposit(20) } } + 5.times.map { Thread.new { ilisses.withdraw(20) } }

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ilisses = Account.new(100) threads = 5.times.map { Thread.new { ilisses.deposit(20) } } + 5.times.map { Thread.new { ilisses.withdraw(20) } } threads.each(&:join) puts ilisses.amount

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ilisses = Account.new(100) 5.times { threads = 5.times.map { Thread.new { ilisses.deposit(20) } } + 5.times.map { Thread.new { ilisses.withdraw(20) } } threads.each(&:join) puts ilisses.amount ilisses = Account.new(100) }

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120 80 100 80 120

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Elixir

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list = [1, 2, 3] List.delete_at(list, -1) list ++ [4] IO.inspect(list) # => [1, 2, 3]

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list = [1, 2, 3] # A ordem não importa List.delete_at(list, -1) list ++ [4] IO.inspect(list) # => [1, 2, 3]

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list = [1, 2, 3] # A ordem importa list = List.delete_at(list, -1) list = list ++ [4] IO.inspect(list) # => [1, 2, 4]

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Se eu quiser compartilhar valores?

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{:ok, ulice_account} = Agent.start_link(fn -> 100 end) deposit_20 = fn -> Agent.update(ulice_account, fn amount -> Process.sleep(100) amount + 20 end) end withdraw_20 = fn -> Agent.update(ulice_account, fn amount -> Process.sleep(100) amount - 20 end) end

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deposit_20.() withdraw_20.() IO.inspect Agent.get(ulice_account, fn amount -> amount end) # 100

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Task.async(deposit_20) Task.async(withdraw_20)

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for _i <- 1..5, do: Task.async(deposit_20) for _i <- 1..5, do: Task.async(withdraw_20)

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deposits = for _i <- 1..5, do: Task.async(deposit_20) withdraws = for _i <- 1..5, do: Task.async(withdraw_20) Enum.each(deposits ++ withdraws, &(Task.await/1)) IO.inspect Agent.get(ulice_account, fn amount -> amount end)

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for _i <- 1..5 do deposits = for _i <- 1..5, do: Task.async(deposit_20) withdraws = for _i <- 1..5, do: Task.async(withdraw_20) Enum.each(deposits ++ withdraws, &(Task.await/1)) IO.inspect Agent.get(ulice_account, fn amount -> amount end) end Agent.stop(ulice_account)

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Imutabilidade no Ruby?

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User = Struct.new(:name) list = [User.new("Bob"), User.new("Anna")] list.freeze list.push(User.new("July")) # => RuntimeError: can't modify frozen Array list[0].name = "Ted" puts list.inspect # => [#, # ]

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Compartilhar valor no Ruby?

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https://github.com/ruby- concurrency/concurrent- ruby

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✅ Imutabilidade ✅ Funções ✅ Código declarativo

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Obrigado!