kv.exs

defmodule KV do
  def start_link do
    Task.start_link(fn -> loop(%{}) end)
  end

  defp loop(map) do
    receive do
      {:get, key, caller} ->
        send caller, Map.get(map, key)
        loop(map)
      {:put, key, value} ->
        loop(Map.put(map, key, value))
    end
  end
end

usage.exs

my_pid = self()

{:ok, pid} = KV.start_link
send pid, {:put, :hello, "james"}
send pid, {:get, :hello, my_pid}

receive do
  value ->
    IO.puts(value)  # => james
end