Exploring Coroutines in PHP

>> This would require a yield to syntax, which doesn't exist.

There is however the 'yield from' statement.

I'd use `yield from` more if I didn't have to re-index arrays before yielding from them:

    function numbers() {
      yield from [1,2,3];
      yield from [4,5,6];
    };
    
    foreach (numbers() as $k => $v) { echo "$k => $v\n"; }
    0 => 1
    1 => 2
    2 => 3
    0 => 4
    1 => 5
    2 => 6

PHP generators/iterators is a hot mess. I don't know any other language which forces iterators to output a key for `foreach(... as $key => ...)`.