Intercept and print compile errors in a nicer way.

lib/display.ex

@@ -24,6 +24,11 @@ defmodule Display do
     "Assertion failed in #{source_file(module)}:#{line_number(expr)}"
   end
 
+  def format_compile_error(error) do
+    trace = System.stacktrace |> Enum.take(2)
+    IO.puts(format_red(Exception.format(:error, error, trace)))
+  end
+
   defp line_number({_, [line: line], _}) do
     line
   end

lib/watcher.ex

@@ -3,8 +3,12 @@ defmodule Watcher do
 
   def callback(file, events)  do
     if Enum.member?(events, :modified) do
+      try do
         [{mod, _}] = Code.load_file(file)
         Runner.run(mod)
+      rescue
+        e -> Display.format_compile_error(e)
+      end
     end
   end
 end