Semantics

Semantic rules:

• Class called Driver should not have any formals because it is the entry point
• No shadowing of variables whatsoever
• Names in typed arms should be unique
• Upon overriding a function, the formal types should be superset equals of parent level formal types
• Match arms should narrow down that type and not broaden it
• No duplicate class name
• Any is the root type
• If class does not extend any other class, then it is implicitly extending Any