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?

{
    if (node)
    {
        container.push_back(std::move(node->as<ASTLiteral &>().value));
        node.reset();
    }
    ASTPtr literal;
    ParserLiteral literal_p;
    ParserToken comma_p(TokenType::Comma);
    ParserToken colon_p(TokenType::Colon);
    ParserToken end_p(TokenType::ClosingCurlyBrace);
    while (true)
    {
        if (end_p.ignore(pos, expected))
        {
            node = std::make_shared<ASTLiteral>(std::move(container));
            break;
        }