title: Letting the ruby environment know the file location
body: <p>While creating a <a href="https://github.com/runefs/Moby" rel="nofollow">gem</a> for DCI I've found the need to be able to tell the environment the location in source of specific expressions.</p>
  
  <p>The reason being that in my particular cse most of the code is handed to <code>instance_eval</code> giving the location of the instance_eval as the error location. However for debugging purposes I'd like to be able to flag where the actual error location is.</p>
  
  <pre><code>context :MyContext do
    role :foo do
      def bar
        player.baz
      end
    end
  end
  </code></pre>
  
  <p>Say that the above code is incorrect, that the object identified by <code>player</code> doesn't have a method called baz. I'd like the runtime to fail and indicate the 4th line above as the error location and not an arbitrary line in the source of the gem</p>
  
  <p>I'll be able to instrument the code to update values as expressions are evaluated, my problem is I don't know what to update</p>