def closure(self) -> List[ParserItem]:
result = [self._item]
accumulator = [self._item]
while accumulator:
for item in accumulator:
if item.has_next:
for rule in self._grammar.rules_of(item.next):
if ParserItem.item_for(rule) not in result:
accumulator.append(ParserItem.item_for(rule))
result.append(ParserItem.item_for(rule))
accumulator.remove(item)
return result
def __init__(self, grammar: ContextFreeGrammar):
self.__grammar = grammar
extended = self.__grammar.extend()
item = ParserItem.item_for(extended.rules_of(NonTerminal("E"))[0])
items = Closure(item, extended).closure()
self.__start = State(items, self.__grammar)
self.__transitions = []
self.__states = [self.__start]
self.__build(self.__start, self.__transitions, self.__states)
def test_when_generating_closure_expect_valid_items(self):
# declarations:
extended = self.grammar.extend()
item = ParserItem.item_for(extended.rules_of(NonTerminal("E"))[0])
# when:
items = Closure(item, extended).closure()
# then:
self.assertEqual(items, [
ParserItem.from_string('E -> . S'),
ParserItem.from_string('S -> . a A')
])
def test_when_is_going_to_next_state_expect_valid_next_state(self):
# declarations:
extended = self.grammar.extend()
item = ParserItem.item_for(extended.rules_of(NonTerminal("E"))[0])
items = Closure(item, extended).closure()
state = State(items, self.grammar)
# when
actual = state.go_to(Symbol("a"))
# then:
self.assertEqual(actual.items, [
ParserItem.from_string('S -> a . A'),
ParserItem.from_string('A -> . b A'),
ParserItem.from_string('A -> . c')
])