My own notes in explains the chain.exs in Programming Elixir, Chapter 12

chain.exs

defmodule Chain do
  
  # There are a couple of interesting things to note in this example.
  # Take a look at the 'counter' function:
  #   It takes in a pid, NOT 'n'. 
  #   'n' will be received in the form of a message (i.e. pid <- msg )
  # In a sense, we are 'loading/setting up' the function first.
  def counter(next_pid) do    
    receive do
      n -> 
        next_pid <- n + 1
    end
  end


  def create_processes(n) do
    # I thought of this like a domino. Enum.reduce 'prepares' all the processes
    # by passing in the arguments to the functions.

    last = Enum.reduce 1..n, self, 
                       fn(_,send_to) -> spawn(Chain, :counter, [send_to]) end 

    # This is when the first 'domino' starts to topple the rest (i.e. kickstarts the chain reaction)
    last <- 0

    # So how did we come to here? 
    # Recall what is passed as the first argument? 'self'! 
    # So, 'self' will be the very last to be sent the message.
    # By then, we would have our answer ready.
    receive do
      final_answer -> 
        "Result is #{final_answer}"
    end
  end

  def run(n) do
    IO.puts inspect :timer.tc(Chain, :create_processes, [n])
  end
    
end