classes.php

CartesianIterator.php

<?php
class CartesianIterator implements IteratorAggregate {
    private $first;
    private $second;
    private $add;

    public function __construct(iterable $first, iterable $second, callable $add) {
        $this->first = $first;
        $this->second = $second;
        $this->add = $add;
    }

    protected function add(){
      return call_user_func_array($this->add, func_get_args());
    }

    public function getIterator() {
      foreach($this->first as $a){
          foreach($this->second as $b){
            yield $this->add($a, $b);
          }
      }
    }
}

SumIterator.php

<?php

class SumIterator implements IteratorAggregate {
    private $iterables = [];

    public function __construct(...$iterables) {
        $this->iterables = $iterables;
    }

    public function append(iterable $it)
    {
        $this->iterables[] = $it;
    }

    public function getIterator() {
        foreach($this->iterables as $it){
            foreach($it as $value){
                yield $value;
            }
        }
    }
}