Recursive Generator

<?php

function foo() {
    static $f = 0;
    yield ++$f;
    yield from goo();
}

function goo() {
    static $g = 'a';
    yield ++$g;
    yield from foo();
}

foreach (foo() as $foo) {
    print $foo.PHP_EOL;
}

?>

Generators in PHP, when using the yield keyword, can become recursive through the use of the yield from construct. This allows a generator to delegate part of its iteration to another generator, creating a chain of generators. However, this recursive behavior is only effective when the generator is consumed by an external iteration mechanism such as a foreach() loop or a function like iterator_to_array(). Without such iteration, the recursive yielding will not be triggered or evaluated.

See Also

• recursive yielding functions [Try me]

PHP Features

• yield

• yield-from

• recursion

• generator

Last updated: 14 July 2026