Before the release of PHP 4, the language didn't embrace the Object-Oriented paradigm. Back then, the usual way of writing applications was by using procedures and global state. Concepts like Separation of Concerns (SoC) and Model-View-Controller (MVC) were alien among the PHP community. The example below is an application written in this traditional way, where applications were composed of many front controllers mixed with HTML code. During this time, Infrastructure-, Presentation-, UI-, and Domain-layer code were all tangled together:

include __DIR__ . '/bootstrap.php';

$link = mysql_connect('localhost', 'a_username', '4_p4ssw0rd');

if (!$link) {
    die('Could not connect: ' . mysql_error());
}

mysql_set_charset('utf8', $link);
mysql_select_db('my_database', $link);

$errormsg = null ;
if (isset($_POST['submit'] && isValid($_POST['post'])) {
    $post = getFrom($_POST['post']);
    mysql_query('START TRANSACTION', $link);
    $sql = sprintf(
        "INSERT...