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?

{
    ParserIdentifier id_parser;
    ParserKeyValuePairsList pairs_list_parser;
    ASTPtr identifier;
    ASTPtr expr_list_args;
    if (!id_parser.parse(pos, identifier, expected))
        return false;
    bool left_bracket_found = false;
    if (pos.get().type != TokenType::OpeningRoundBracket)
    {
        if (!brackets_can_be_omitted)
             return false;
    }
    else