How do you walk a paginated API?

gistfile1.php

<?php

function walk($callback)
{
    $page = 1;
    do {
        $results = fetch($page++, 100);

        foreach ($results as $result) {
            call_user_func($callback, $result);
        }
    } while (100 == count($results);
}

function fetch($page, $perPage)
{
    // ...
}