added questions for optional type and type guard

README.md

@@ -126,6 +126,11 @@ class Foo(EnvExperiment):
 * Type variable cannot occur alone in the result type, i.e. must be bound to the
   input parameters.
 
+Questions:
+* Should we support things like optional type? (like the one in rust)
+* Would it be better to assert on the type variable directly instead of
+  `type(x)` for type guards?
+
 ## Dynamic Dispatch
 Type annotations are invariant, so subtype (derived types) cannot be used
 when the base type is expected. Example: