def try_removing_useless_rules(self):
gen_graph = DirectedGraph()
for rule in self.rules:
for symbol in rule.unique_symbols():
if not symbol.is_terminal():
gen_graph.add_vertex(symbol)
for symbol in rule.tail:
if not symbol.is_terminal():
gen_graph.add_edge(rule.head, symbol)
removed = []
for s in gen_graph.get_unreachable(self.start):
to_del = self.rules_by_head(s)
for rule in to_del:
i = self.index(rule)
removed.append(i)
if removed:
self.__assert_parent__()
removed.sort()
for i in reversed(removed):
del self.rules[i]
self.__commit_transform__(Unremove(removed))
return len(removed)
