def union_nfa(self, nfa: NFA, unioning_state: State = None) -> None:
"""
union_nfa
Add a union from the last open group (or initial state) to existing NFA.
:param nfa: The existing NFA.
:param unioning_state: An optional state to union from (otherwise: last open group)
"""
start_union = unioning_state if unioning_state else self.open_groups[-1]
self.union_in_progress.append((start_union, self.last_state))
logging.debug('Opening union: ' + str((start_union, self.last_state)))
if start_union in nfa.accepting_states:
nfa.accepting_states.remove(start_union)
# If my open group is at the initial state, make a new state
if start_union == nfa.initial_state:
self.last_state = nfa.replace_initial()
# Otherwise, connect a new epsilon path out of the
# open group state for the other part of the union
else:
self.last_state = nfa.add_epsilon_connector(start_union)
