auto list = [](auto ...xs) { 
    return [=](auto access) { return access(xs...); }; 
}; 

auto head = [](auto xs) { 
    return xs([](auto first, auto ...rest) { return first; }); 
}; 

auto tail = [](auto xs) { 
    return xs([](auto first, auto ...rest) { return list(rest...); }); 
}; 

auto length = [](auto xs) { 
    return xs([](auto ...z) { return sizeof...(z); }); 
}; 

int len = length(list(1, '2', "3"));  // 3