<SYSTEM_TASK:>
Solve the following problem using Python, implementing the functions described below, one line at a time
<END_TASK>
<USER_TASK:>
Description:
 def create_graph_rules(address_mapper):
 """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. """


  @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),
  ]