index.php

// Get autoloader
require_once "vendor/autoload.php";

// Start router
$klein = new \Klein\Klein();

// INDEX PAGE
$klein->respond('GET', '/', function ($request, $response, $service, $app) {
    require "controllers/index.php";
});

// Foo
$klein->respond('GET', '/foo', function ($request, $response, $service, $app) {
    require "controllers/foo.php";
});

$klein->dispatch();