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?

{
    switch (type)
    {
        case TokenType::Error:
            return "Unrecognized token";
        case TokenType::ErrorMultilineCommentIsNotClosed:
            return "Multiline comment is not closed";
        case TokenType::ErrorSingleQuoteIsNotClosed:
            return "Single quoted string is not closed";
        case TokenType::ErrorDoubleQuoteIsNotClosed:
            return "Double quoted string is not closed";
        case TokenType::ErrorBackQuoteIsNotClosed:
            return "Back quoted string is not closed";
        case TokenType::ErrorSingleExclamationMark:
            return "Exclamation mark can only occur in != operator";
        case TokenType::ErrorSinglePipeMark:
            return "Pipe symbol could only occur in || operator";
        case TokenType::ErrorWrongNumber:
            return "Wrong number";
        case TokenType::ErrorMaxQuerySizeExceeded:
            return "Max query size exceeded";
        default:
            return "Not an error";
    }
}
}