int disambiguator(struct state *old, struct state *new) {
    // printf("Old tree: ");
    // print_parse_tree2(old);
    // printf("New tree: ");
    // print_parse_tree2(new);

    if (old->start_idx != new->start_idx) {
        // printf("\t\tIGNORING "); print_parse_tree2(old);
        // printf("\t\tVS:      "); print_parse_tree2(new);
        return 2;
    }

    // Prefer the earlier parsings in the grammar when two entirely different
    // productions are taken.
    if (old->production_id != new->production_id)
        return old->production_id < new->production_id
             ? 0 : 1;

    // If they're the same production ...
    prod_id_t prod = old->production_id;
    if (PRODUCTION_ID_TO_SYMBOL[prod] == SYMBOL_EXPR) {
        if (PRODUCTION_ID_TO_PRODUCTION[prod][1] == SYMBOL_OP) {
            struct token *old_tok = find_token(old, 1),
                         *new_tok = find_token(new, 1);
            char *old_s = old_tok->string, *new_s = new_tok->string;
            const char *precedence[] = {".", "->", "*", "/", "%", "+", "-",
                "<<", ">>", "<", "<=", ">", ">=", "==", "!=", "&", "|", "&&",
                "||", "=", "+=", "-=", "*=", "/=", "%=", "<<=", ">>=", "&=",
                "^=", "|=", ",", 0};
            if (strcmp(old_s, new_s)) {
                for (const char **p = precedence; *p; p++) {
                    if (!strcmp(old_s, *p)) {
                        return 1;
                    } else if (!strcmp(new_s, *p)) {
                        return 0;
                    }
                }
                // BAD!
                return 2;
            } else {
                // Associate RIGHT
                if (old_tok < new_tok)      return 1;
                else if (old_tok > new_tok) return 0;
            }
        }
    }
    printf("TOTALLY UNKNOWN!\n");
    return 2;
}