Pros:
- it is convenient to type and read numbers this way;
- Ada, Perl, C++, Go and Rust already support that;
- can support thousands as well as lakhs and crores;

Cons:
- standard SQL does not have this support;
- PostgreSQL treat `SELECT 1_000_000` as number one with `_000_000` alias: http://sqlfiddle.com/#!17/0a28f/400
- C++ has `1'000'000` instead of `1_000_000`;

What do you think?

}
    else if (pos->type == TokenType::BareWord)
    {
        node = std::make_shared<ASTIdentifier>(String(pos->begin, pos->end));
        ++pos;
        return true;
    }
    else if (allow_query_parameter && pos->type == TokenType::OpeningCurlyBrace)
    {
        ++pos;
        if (pos->type != TokenType::BareWord)
        {
            expected.add(pos, "substitution name (identifier)");
            return false;
        }
        String name(pos->begin, pos->end);
        ++pos;
        if (pos->type != TokenType::Colon)
        {
            expected.add(pos, "colon between name and type");
            return false;
        }
        ++pos;
        if (pos->type != TokenType::BareWord)
        {
            expected.add(pos, "substitution type (identifier)");
            return false;
        }
        String type(pos->begin, pos->end);
        ++pos;