{%hackmd SyQbZi4Mr %} ## Not familiar with Elixir? Let me do a simple intro in 30 minutes 借用您半小時，請問有聽過 elixir 嗎？ by [PastLeo](https://pastleo.me), a little developer at [5xruby](https://5xruby.tw) --- ## Outline * Functional Syntax * Macro * Process, message passing * Application * A database migration tool * Resources --- ## Functional Syntax --- #### let's say I want a function... ```elixir Demo.sum_ints("1,3,asdf,5") # => 9 ``` --- ## let me demo how to create this function ```elixir test "sum_ints" do assert Demo.sum_ints( "1,3,asdf,5" ) == 9 end ``` --- ### pipe, pattern matching ```elixir defmodule Demo do def sum_ints(str) do String.split(str, ",") |> Enum.map(&Integer.parse/1) |> Enum.flat_map(&valid_int/1) |> Enum.sum() end defp valid_int({int, _}), do: [int] defp valid_int(_), do: [] end ``` --- ## Macro --- #### a glimpse of ecto a bridge between database in elixir ```elixir query = from u in "users", where: u.age > 18, select: u.name ``` [Ecto.Query document](https://hexdocs.pm/ecto/Ecto.Query.html#content) --- #### how macro works ```elixir quote do 1 + 1 end ``` ```elixir defmodule Demo.Macro do defmacro hello(ast) do IO.inspect(ast) end end ``` --- #### let's bring `begin` from ruby ```elixir begin do 1/0 rescue :error end # => :error ``` --- #### `quote` and `unquote` ```elixir defmacro begin( do: do_block, rescue: rescue_block ) do quote do try do unquote(do_block) rescue _ -> unquote(rescue_block) end end end ``` --- #### actually... * [defmacro if](https://github.com/elixir-lang/elixir/blob/v1.6.4/lib/elixir/lib/kernel.ex#L2840) * [defmacro defmodule](https://github.com/elixir-lang/elixir/blob/v1.6.4/lib/elixir/lib/kernel.ex#L3589) * [defmacro def](https://github.com/elixir-lang/elixir/blob/v1.6.4/lib/elixir/lib/kernel.ex#L3834) * [defmacro defmacro](https://github.com/elixir-lang/elixir/blob/v1.6.4/lib/elixir/lib/kernel.ex#L3886) --- ## Process, message passing --- #### why concurrent/parallel is so hard  [reddit 'Perfect demonstration of a race condition.'](https://www.reddit.com/r/ProgrammerHumor/comments/2skae8/perfect_demonstration_of_a_race_condition/) --- #### start a process ```elixir spawn(fn -> ... end) ``` not system process nor thread --- #### start a lot of processes ```elixir Enum.each(1..10000, fn(_) -> spawn(fn -> IO.inspect(self()) end) end) ``` --- #### Message passing ```elixir me = self() spawn(fn -> send(me, self()) end) receive do x -> IO.inspect(x) end ``` --- #### Fibonacci Service ```elixir defmodule Demo.Process do def fibonacci_service do receive do x -> fibonacci(x) |> IO.puts() end fibonacci_service() end end ``` --- #### One step forward: OTP * shorthand of [Open Telecom Platform](https://en.wikipedia.org/wiki/Open_Telecom_Platform) * process communication * [GenServer](https://hexdocs.pm/elixir/GenServer.html) * process maintaining * [Supervisor](https://hexdocs.pm/elixir/Supervisor.html) * code replacement --- #### Tip of the iceberg of phoenix server processes  --- ## Application #### the migration tool --- #### Purpose  --- #### How to match ```elixir [1, 2, 3] -- [1, 3] # => [2] ``` ```elixir [source html nodes] -- [all possible html nodes for a template] == [] ``` ```elixir [required html nodes for a template] -- [source html nodes] == [] ``` --- #### using [GenStage](https://hexdocs.pm/gen_stage/GenStage.html) and [Flow](https://hexdocs.pm/flow/Flow.html) to do full migrate * postgres streaming producer * data source is only one big query * use `Flow` to utilize all CPUs * result speed: * around 86000+ users, each of them has 5 pages in average * 430000+ pages in 20 minutes --- #### listening to postgres trigger * user changed * `|>` postgres trigger * `|>` postgres channel * `|>` elixir process event loop * `|>` re-migrate on the specific user * [postgrex notification module](https://github.com/elixir-ecto/postgrex/blob/master/lib/postgrex/notifications.ex) --- #### more processes * states: * currently being migrated user * excluded user * queued user * success rate, statistic * progress bar --- #### how it looks like when running  --- ## Learning Resource * [Elixirschool](https://elixirschool.com/en/) * [Elixir official guide](https://elixir-lang.org/getting-started/introduction.html) * [Elixir for Programmers (Video, Dave Thomas)](https://codestool.coding-gnome.com/courses/elixir-for-programmers) * [Elixir official learning resources](https://elixir-lang.org/learning.html) --- ## Thanks for listening! #### Any questions?