Almost a year ago Igor Wiedler wrote three articles on his blog about the state of functional programming in PHP.

The first article explores iteration. You'll learn to turn this

$admins = [];
foreach ($users as $user) {
    if (is_admin($user)) {
        $admins[] = $user;

into this

use function iter\filter;
$admins = filter('project\user\is_admin', $users);

In the second one he explains a very nice way to traverse an associative array. How you currently do it:

$baz = (isset($data['foo']['bar']['baz'])) ? $data['foo']['bar']['baz'] : null;

How you'll do it in the future:

use function igorw\get_in;
$baz = get_in($data, ['foo', 'bar', 'baz']);

The final article shows you a nice syntax to handle objects that return null-values.

All the articles mention libraries that you can use in your code today.