Extracted watcher and runner into supervision tree.

lib/display.ex

@@ -16,34 +16,6 @@ defmodule Display do
     {:noreply, %{state | clear_screen: false}}
   end
 
-  def handle_cast({:invalid, koan, modules}, state) do
-    Notifications.invalid_koan(koan, modules)
-    |> IO.puts
-
-    {:noreply, state}
-  end
-
-  def handle_cast({:show_failure, failure, module, name}, state) do
-    format(failure, module, name)
-    |> IO.puts
-
-    {:noreply, state}
-  end
-
-  def handle_cast({:show_compile_error, error}, state) do
-    Failure.show_compile_error(error)
-    |> IO.puts
-
-    {:noreply, state}
-  end
-
-  def handle_cast(:congratulate, state) do
-    Notifications.congratulate
-    |> IO.puts
-
-    {:noreply, state}
-  end
-
   def handle_cast(:clear_screen, state = %{clear_screen: true}) do
     IO.puts(ANSI.clear)
     IO.puts(ANSI.home)
@@ -55,19 +27,23 @@ defmodule Display do
   end
 
   def invalid_koan(koan, modules) do
-    GenServer.cast(__MODULE__, {:invalid, koan, modules})
+    Notifications.invalid_koan(koan, modules)
+    |> IO.puts
   end
 
   def show_failure(failure, module, name) do
-    GenServer.cast(__MODULE__, {:show_failure, failure, module, name})
+    format(failure, module, name)
+    |> IO.puts
   end
 
   def show_compile_error(error) do
-    GenServer.cast(__MODULE__, {:show_compile_error, error})
+    Failure.show_compile_error(error)
+    |> IO.puts
   end
 
   def congratulate do
-    GenServer.cast(__MODULE__, :congratulate)
+    Notifications.congratulate
+    |> IO.puts
   end
 
   def clear_screen do

lib/elixir_koans.ex

@@ -7,7 +7,9 @@ defmodule ElixirKoans do
 
     children = [
       worker(Display, []),
-      worker(Tracker, [])
+      worker(Tracker, []),
+      worker(Runner, []),
+      worker(Watcher, [])
     ]
 
     opts = [strategy: :one_for_one, name: ElixirKoans.Supervisor]

lib/meditate.ex

@@ -7,8 +7,6 @@ defmodule Mix.Tasks.Meditate do
   def run(args) do
     Application.ensure_all_started(:elixir_koans)
     Code.compiler_options(ignore_module_conflict: true)
-    {:ok, watcher} = Watcher.start
-    Process.monitor(watcher)
 
     Options.start(args)
 
@@ -22,17 +20,12 @@ defmodule Mix.Tasks.Meditate do
     |> Runner.modules_to_run
 
     Tracker.set_total(modules)
+    Tracker.notify_on_complete(self())
 
     Runner.run(modules)
 
-    if Tracker.complete? do
-      Display.congratulate
-      exit(:normal)
-    end
-
-    receive do
-      {:DOWN, _references, :process, ^watcher, _reason} -> nil
-    end
+    Tracker.wait_until_complete()
+    Display.congratulate()
   end
 
   defp ok?(koan) do

lib/runner.ex

@@ -1,4 +1,5 @@
 defmodule Runner do
+  use GenServer
 
   def koan?(koan) do
     Keyword.has_key?(koan.__info__(:exports), :all_koans)
@@ -27,14 +28,38 @@ defmodule Runner do
   def modules_to_run, do: Options.initial_koan |> modules_to_run
   def modules_to_run(start_module), do: Enum.drop_while(modules(), &(&1 != start_module))
 
-  def run(modules) do
-    Display.clear_screen()
-
-    modules
-    |> Enum.take_while( &(run_module(&1) == :passed))
+  def start_link do
+    GenServer.start_link(__MODULE__, [], name: __MODULE__)
   end
 
-  def run_module(module) do
+  def handle_cast({:run, modules}, _) do
+    flush()
+    send(self(), :run_modules)
+    {:noreply, modules}
+  end
+
+  def handle_info(:run_modules, []) do
+    {:noreply, []}
+  end
+
+  def handle_info(:run_modules, [module | rest]) do
+    Display.clear_screen()
+
+    case run_module(module) do
+      :passed ->
+        send(self(), :run_modules)
+        {:noreply, rest}
+
+      _ ->
+        {:noreply, []}
+    end
+  end
+
+  def run(modules) do
+    GenServer.cast(__MODULE__, {:run, modules})
+  end
+
+  defp run_module(module) do
     module
     |> Execute.run_module(&track/3)
     |> display
@@ -48,4 +73,12 @@ defmodule Runner do
     :failed
   end
   defp display(_), do: :passed
+
+  defp flush do
+    receive do
+      _ -> flush()
+    after
+      0 -> :ok
+    end
+  end
 end

lib/tracker.ex

@@ -1,12 +1,19 @@
 defmodule Tracker do
   alias __MODULE__
 
-  defstruct total: 0, koans: MapSet.new(), visited_modules: MapSet.new()
+  defstruct total: 0,
+    koans: MapSet.new(),
+    visited_modules: MapSet.new(),
+    on_complete: :noop
 
   def start_link do
     Agent.start_link(fn -> %Tracker{} end, name: __MODULE__)
   end
 
+  def notify_on_complete(pid) do
+    Agent.update(__MODULE__, fn state -> %{state | on_complete: pid} end)
+  end
+
   def set_total(modules) do
     total = modules
     |> Enum.flat_map(&(&1.all_koans))
@@ -17,6 +24,19 @@ defmodule Tracker do
 
   def completed(module, koan) do
     Agent.update(__MODULE__, &mark_koan_completed(&1, module, koan))
+    if complete?() do
+      Agent.cast(__MODULE__, fn state ->
+        send(state.on_complete, {self(), :complete})
+        state
+      end)
+    end
+  end
+
+  def wait_until_complete() do
+    pid = Process.whereis(Tracker)
+    receive do
+      {^pid, :complete} -> :ok
+    end
   end
 
   defp mark_koan_completed(state, module, koan) do

lib/watcher.ex

@@ -1,14 +1,13 @@
 defmodule Watcher do
   use ExFSWatch, dirs: ["lib/koans"]
 
+  def start_link do
+    start()
+  end
+
   def callback(file, events)  do
     if Enum.member?(events, :modified) do
       file |> normalize |> reload
-
-      if Tracker.complete? do
-        Display.congratulate
-        exit(:normal)
-      end
     end
   end