Flatten

function flatten($inputArray) {
    $output = '';
    foreach ($inputArray as $element) {
        if (is_array($element) == true) {
            $output .= flatten($element);
        }
        else {
            $output .= $element;
        }
    }

    return $output;
}


$print = array(
    'orange',
    'green',
    array(
        'yellow',
        'white'
    )
);

echo flatten($print);