code: def create_graph_rules(address_mapper):
    
  
    @rule(AddressMapper, [])
    def address_mapper_singleton():
      return address_mapper
  
    return [
      address_mapper_singleton,
      # BUILD file parsing.
      hydrate_struct,
      parse_address_family,
      # Spec handling: locate directories that contain build files, and request
      # AddressFamilies for each of them.
      addresses_from_address_families,
      # Root rules representing parameters that might be provided via root subjects.
      RootRule(Address),
      RootRule(BuildFileAddress),
      RootRule(BuildFileAddresses),
      RootRule(Specs),
    ]
docs: Creates tasks used to parse Structs from BUILD files.
  
    :param address_mapper_key: The subject key for an AddressMapper instance.
    :param symbol_table: A SymbolTable instance to provide symbols for Address lookups.