Demonstrates how to implement recursive generators in PHP 5.5+

recursive-generator-php55.php

<?php
function walkTree($tree, $depth = 0) {
	foreach ($tree as $key => $value) {
		yield ['depth' => $depth, 'name' => $key];
		if (is_array($value)) {
			foreach (walkTree($value, $depth + 1) as $yeilded) {
				yield $yeilded;
			}
		}
	}
}
$tree = [
	'fruit' => [
		'apple' => [
			'granny smith' => null,
		],
		'pear' => null,
	],
	'vegatable' => [
		'avocado' => null,
		'tomato' => null,
		'potato' => null,
	],
	'meat' => [
		'chicken' => null,
		'pork' => null,
		'beef' => null,
		'kangaroo' => null,
	],
];
// echo '<pre>' . PHP_EOL;
foreach (walkTree($tree) as $node) {
	echo str_repeat('  ', $node['depth']) . '- ' . $node['name'] . PHP_EOL;
}
// echo '</pre>' . PHP_EOL;
/*
OUTPUT:
- fruit
  - apple
    - granny smith
  - pear
- vegatable
  - avocado
  - tomato
  - potato
- meat
  - chicken
  - pork
  - beef
  - kangaroo
 */