@@ 113,7 113,13 @@ watchShaderProgram manager dir vsFileRel fsFileRel = do
   vsInitial <- liftIO $ B.readFile vsFileAbs
   fsInitial <- liftIO $ B.readFile fsFileAbs
 
-  -- Watch the dir for changes to the files we're interested in
+  -- Watch the dir for changes to the files we're interested in. In
+  -- this demo program, we only care about one of the constructors of
+  -- a 'FS.Event'. This means we can get away with
+  -- 'mapMaybe'.
+  --
+  -- Exercise: Learn how to use 'fan' to efficiently split an 'Event t
+  -- FS.Event' into four different 'Event's.
   let
     onlyModifications (FS.Modified path mtime isDir) = Just (path, mtime, isDir)
     onlyModifications _ = Nothing