cartesian.php

<?php

$options = [
    'a' => [1,2],
    'b' => [1,2,3],
];

function cartesian($array)
{
    if ($array)
    {
        $key = end(array_keys($array));
        if ($values = array_pop($array)) {
            foreach(cartesian($array) as $tuple) {
                foreach($values as $value) {
                    yield $tuple + [$key => $value];
                }
            }
        }
    } else {
        yield[];
    }
}

foreach (cartesian($options) as $tuple) {
    echo json_encode($tuple)."\n";
}