acky.ex

defmodule Acky do

  defmodule Client do
    def start do
      spawn(__MODULE__, :loop, [])
    end

    def loop do
      receive do
        {from, {:ok, result}} ->
          IO.puts "Got result: #{result}"
          from |> send :ok
          loop
        _ -> 
          IO.puts "Unexpected message!"
          loop
      end
    end

  end

  defmodule Server do
    
    def start do
      spawn(__MODULE__, :loop, [ HashDict.new ])
    end

    def loop(cache) do
      receive do
        {:compute, {reply_to, {m, n}}} ->
          case HashDict.fetch(cache, {m, n}) do
            {:ok, result} ->
              IO.puts "[CACHE HIT]: #{result}"
              reply_to |> send({self, {:ok, result}})
              receive do
                _ -> :ok
              end
            :error ->
              result = ackermann(m, n)
              IO.puts "[CACHE MISS]: #{result}"
              cache = cache |> HashDict.put({m,n}, result)
              reply_to |> send({self, {:ok, result}})
          end
          loop(cache)

        :view_cache ->
          IO.inspect cache
          loop(cache)

        :stop -> :ok

        _ -> 
          IO.puts "Unexpected message!"
          loop(cache)
      end
    end

    defp ackermann(0, n), do: n + 1
    defp ackermann(m, 0), do: ackermann(m-1, 1)
    defp ackermann(m, n), do: ackermann(m-1, ackermann(m,n-1))

  end
end


client = Acky.Client.start
server = Acky.Server.start
server |> send {:compute, {client, {3,2}}}
server |> send {:compute, {client, {4,1}}}