feat: add toy registry

other/simple_registry.ex

@@ -0,0 +1,37 @@
+defmodule SimpleRegistry do
+  use GenServer
+
+  def start_link do
+    GenServer.start_link(__MODULE__, nil, name: __MODULE__)
+  end
+
+  def register(name) when is_atom(name) do
+    Process.link(Process.whereis(__MODULE__))
+
+    if :ets.insert_new(__MODULE__, {name, self()}) do
+      :ok
+    else
+      :error
+    end
+  end
+
+  def whereis(name) when is_atom(name) do
+    case :ets.lookup(__MODULE__, name) do
+      [{^name, value}] -> value
+      [] -> nil
+    end
+  end
+
+  @impl GenServer
+  def init(_) do
+    Process.flag(:trap_exit, true)
+    :ets.new(__MODULE__, [:named_table, :public])
+    {:ok, nil}
+  end
+
+  @impl GenServer
+  def handle_info({:EXIT, pid, _reason}, state) do
+    :ets.match_delete(__MODULE__, {:_, pid})
+    {:noreply, state}
+  end
+end