Method parse_sequence

smallthinker/src/llama-grammar.cpp:340–511

}

const char * llama_grammar_parser::parse_sequence(
        const char         * src,
        const std::string  & rule_name,
        llama_grammar_rule & rule,
        bool               is_nested) {
    size_t last_sym_start = rule.size();
    const char * pos = src;

    auto handle_repetitions = [&](int min_times, int max_times) {

        if (last_sym_start == rule.size()) {
            throw std::runtime_error(std::string("expecting preceding item to */+/?/{ at ") + pos);
        }

        // apply transformation to previous symbol (last_sym_start to end) according to
        // the following rewrite rules:
        // S{m,n} --> S S S (m times) S'(n-m)
        //            S'(x)   ::= S S'(x-1) |
        //            (... n-m definitions of these S' rules ...)
        //            S'(1)   ::= S |
        // S{m,} -->  S S S (m times) S'
        //            S'     ::= S S' |
        // S*     --> S{0,}
        //        --> S'     ::= S S' |
        // S+     --> S{1,}
        //        --> S S'
        //            S'     ::= S S' |
        // S?     --> S{0,1}
        //        --> S'
        //            S'     ::= S |

        llama_grammar_rule prev_rule(rule.begin() + last_sym_start, rule.end());
        if (min_times == 0) {
            rule.resize(last_sym_start);
        } else {
            // Repeat the previous elements (min_times - 1) times
            for (int i = 1; i < min_times; i++) {
                rule.insert(rule.end(), prev_rule.begin(), prev_rule.end());
            }
        }

        uint32_t last_rec_rule_id = 0;
        auto n_opt = max_times < 0 ? 1 : max_times - min_times;

        llama_grammar_rule rec_rule(prev_rule);
        for (int i = 0; i < n_opt; i++) {
            rec_rule.resize(prev_rule.size());
            uint32_t rec_rule_id = generate_symbol_id( rule_name);
            if (i > 0 || max_times < 0) {
                rec_rule.push_back({LLAMA_GRETYPE_RULE_REF, max_times < 0 ? rec_rule_id : last_rec_rule_id});
            }
            rec_rule.push_back({LLAMA_GRETYPE_ALT, 0});
            rec_rule.push_back({LLAMA_GRETYPE_END, 0});
            add_rule( rec_rule_id, rec_rule);
            last_rec_rule_id = rec_rule_id;
        }
        if (n_opt > 0) {
            rule.push_back({LLAMA_GRETYPE_RULE_REF, last_rec_rule_id});