void ItemSetBuilder::build_successors(const ItemSet& set) {
// reset
for (auto& item : set.m_closure) item.complete = false;
for (auto& item : set.m_closure) {
if (item.complete) continue;
auto& production = m_grammar.get_production(item.production_id());
auto dot = item.dot();
// skip item whose dot is at right end
if (dot >= production.rhs_count()) {
item.complete = true;
continue;
}
auto& symbol = production[dot + 1]; // symbol after dot
// for each item which has 'symbol' after its dot
for (auto& item2 : set.m_closure) {
if (item2.complete) continue;
auto& production2 = m_grammar.get_production(item2.production_id());
auto dot2 = item2.dot();
if (dot2 >= production2.rhs_count()) {
// 'item2' has no successor
item2.complete = true;
continue;
}
auto& symbol2 = production2[dot2 + 1]; // symbol after dot
if (symbol == symbol2) {
// each item becomes complete after contibuting a successor
item2.complete = true;
auto& add = m_curr_item_set.add_kernel(production2, dot2 + 1);
add.lookaheads().resize(m_grammar.symbol_count());
// add backward propagation link
auto& new_node = new_link();
new_node->next = add.backward_plink();
add.backward_plink() = new_node;
new_node->item = &item2;
}
}
// build set from new kernels
auto& new_set = build_item_set();
if (symbol.type() == SymbolType::NONTERMINAL) {
auto& act = set.add_action(symbol, ActionType::GOTO, new_set.id());
}
else {
auto& act = set.add_action(symbol, ActionType::SHIFT, new_set.id());
assert(act.type != ActionType::SSCONFLICT);
}
}
}
