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 (pos->size() > MAX_LENGTH_OF_NUMBER)
    {
        expected.add(pos, "number");
        return false;
    }
    char buf[MAX_LENGTH_OF_NUMBER + 1];
    size_t size = pos->size();
    memcpy(buf, pos->begin, size);
    buf[size] = 0;
    char * start_pos = buf;
    if (*start_pos == '0')
    {
        ++start_pos;
        --size;
        
        if (*start_pos == 'b')
        {
            ++start_pos;
            --size;
            if (parseNumber(start_pos, size, negative, 2, res))
            {
                auto literal = std::make_shared<ASTLiteral>(res);
                literal->begin = literal_begin;
                literal->end = ++pos;
                node = literal;
                return true;
            }
            else
                return false;
        }