middleware callable dispatchers

middleware.php

<?php
// class for a stack of callables
class Dispatcher
{
    protected array $stack;
    public function __construct(array &$stack)
    {
        $this->stack = $stack;
    }
    public function __invoke(RequestInterface $req)
    {
        $handler = array_shift($this->stack);
        return call_user_func($handler, $req, new self($this->stack));
    }
}

// single line function for a stack of callables
$run = function ($req) use (&$stack, &$run) { return call_user_func(array_shift($stack), $req, $run); };