I started playing with boost::lambda and I need some help or some clarification about it

or some hint to better understanding how does it work.

I have this piece of code

using namespace boost::lambda;

using boost::lambda::var;

int main(int argc, char** argv) {

std::vector< int > myList;

myList.push_back(100);

myList.push_back(200);

int interval = 20;

std::for_each( myList.begin(), myList.end(),

(

std::cout << "value: " << _1 << "\n",

std::cout << "interval: " << var( interval ) << "\n",

var( interval )++

));

}

I understood that writing a lambda expression would be a substitute

for writing a functor.

I expected the following result

value: 100

interval: 20

value: 200

interval: 21

Instead I had the following

intervalfirst value: 100

200

Why the strings "interval" and "first" are not written for each value and how can I achieve this?