def _get_next_configuration(self, old_config):
"""Advance to the next configuration."""
transitions = set()
if old_config.remaining_input:
transitions.add(
self._get_transition(old_config.state,
old_config.remaining_input[0],
old_config.stack.top()))
transitions.add(
self._get_transition(old_config.state, '', old_config.stack.top()))
if None in transitions:
transitions.remove(None)
if len(transitions) == 0:
raise exceptions.RejectionException(
'The automaton entered a configuration for which no '
'transition is defined ({}, {}, {})'.format(
old_config.state, old_config.remaining_input[0],
old_config.stack.top()))
if len(transitions) > 1:
raise pda_exceptions.NondeterminismError(
'The automaton entered a configuration for which more'
'than one transition is defined ({}, {}'.format(
old_config.state, old_config.stack.top()))
input_symbol, new_state, new_stack_top = transitions.pop()
remaining_input = old_config.remaining_input
if input_symbol:
remaining_input = remaining_input[1:]
new_config = PDAConfiguration(
new_state, remaining_input,
self._replace_stack_top(old_config.stack, new_stack_top))
return new_config
def _validate_transition_lambda_transition_sibling(self, start_state,
sib_path):
"""Check the given sibling path for adjacent lambda transitions."""
for other_stack_symbol in sib_path:
if (other_stack_symbol in self.transitions[start_state]['ε']):
raise pda_exceptions.NondeterminismError(
'A symbol transition is adjacent to a '
'lambda transition for this DPDA.')