Fix compile error & add extra comment

type_aliases/main.pony

@@ -10,9 +10,12 @@ primitive ColourList
     fun apply(): Array[Colour] =>
         [Red; Green; Blue]
 
-for colour in ColourList().values() do
-    
-end
+actor Main
+    new create(env: Env) =>
+        for colour in ColourList().values() do
+            env.out.print("I should be printing a colour
+                but I don't know how to cast to string")
+        end
 
 // Type aliases can also be used to give simpler names to complex types
 interface HasName

type_expressions/main.pony

@@ -8,6 +8,7 @@ x = ("hi", 3)
 x = ("bye", 7)
 
 // Pony supports tuple unpacking but calls it "destructuring"
+// This assigns "bye" to y and 7 to z
 (var y, var z) = x
 
 // You can access the elements of tuples directly using this