defmodule Example do
  def double(x) do
    :timer.sleep(2000)
    x * 2
  end
end

iex> task = Task.async(Example, :double, [2000])
%Task{pid: #PID<0.111.0>, ref: #Reference<0.0.8.200>}

iex> Task.await(task)
4000

defmodule Example do
  def add(a, b) do
    IO.puts(a + b)
  end
end

iex> spawn(Example, :add, [2, 3])
5
#PID<0.80.0>

# Start a new event manager.
{:ok, pid} = GenEvent.start_link([])

# Define an Event Handler
defmodule LoggerHandler do
  use GenEvent

  # Callbacks

  def handle_event({:log, x}, messages) do
    {:ok, [x | messages]}
  end

  def handle_call(:messages, messages) do
    {:ok, Enum.reverse(messages), []}
  end
end

# Start a new event manager.
{:ok, pid} = GenEvent.start_link([])

# Attach an event handler to the event manager.
GenEvent.add_handler(pid, LoggerHandler, [])
#=> :ok

# Attach an event handler to the event manager.
GenEvent.add_handler(pid, LoggerHandler, [])
#=> :ok

# Send some events to the event manager.
GenEvent.notify(pid, {:log, 1})
#=> :ok

GenEvent.notify(pid, {:log, 2})
#=> :ok

# Call functions on specific handlers in the manager.
GenEvent.call(pid, LoggerHandler, :messages)
#=> [1, 2]

GenEvent.call(pid, LoggerHandler, :messages)
#=> []

defmodule LoggerHandlerWatcher do
  @doc """
    inits the GenServer by starting a new handler
  """
  def init(logger_pid) do
    start_handler(logger_pid)
  end

  @doc """
    handles EXIT messages from the GenEvent handler and restarts it
  """
  def handle_info({:gen_event_EXIT, _handler, _reason}, logger_pid) do
    {:ok, logger_pid} = start_handler(logger_pid)
    {:noreply, logger_pid}
  end

  @doc """
    starts a new handler listening for events on `logger_pid`
  """
  defp start_handler(logger_pid) do
    case GenEvent.add_mon_handler(logger_pid, LoggerHandler, []) do
     :ok ->
       {:ok, logger_pid}
     {:error, reason}  ->
       {:stop, reason}
    end
  end
end

iex> {:ok, agent} = Agent.start_link(fn -> [1, 2, 3] end)
{:ok, #PID<0.65.0>}

iex> Agent.update(agent, fn (state) -> state ++ [4, 5] end)
:ok

iex> Agent.get(agent, &(&1))
[1, 2, 3, 4, 5]

iex> self
#PID<0.115.0>

iex> {:ok, agent} = Agent.start_link(fn -> [] end)
{:ok, #PID<0.123.0>}

iex> Agent.get(agent, fn(_) -> IO.inspect self end)
#PID<0.123.0>

iex> self
#PID<0.115.0>

# They can be named!

iex> Agent.start_link(fn -> [1, 2, 3] end, name: Numbers)
{:ok, #PID<0.74.0>}

iex> Agent.get(Numbers, &(&1))
[1, 2, 3]

iex> table = :ets.new(:meetups, [:set, :protected])
8212

iex> :ets.new(:meetups, [:set, :protected, :named_table])
:user_lookup

iex> :ets.insert(:meetups, {"Kyiv Elixir", "awesome", ["Elixir"]})
true

iex> :ets.lookup(:meetups, "Kyiv Elixir")
{"Kyiv Elixir", "awesome", ["Elixir"]}

iex> :ets.match(:meetups, {:"$1", "awesome", :"_"})
[["Kyiv Elixir"]]

iex> :ets.delete(:meetups, "Kyiv Elixir")
true

iex> :ets.delete(:meetups)
true