Generate Combinations of a set

combos.php

<?php

function generate_combinations($set, $max_depth = INF, $depth = 0) {
	if (! is_array($set)) { trigger_error("Give me an array plox"); }
	if (count($set) <= 1) {
		return array($set);
	}
	if ($depth >= $max_depth) {
		return array($set);
	}
	$mantissa = reset($set);
	$subset = array_slice($set, 1);
	$combinations = generate_combinations($subset, $max_depth, $depth + 1);
	$add_combos = array();
	foreach ($combinations as $subset) {
		$add_combos []= array_merge(array($mantissa), $subset);
	}
	foreach ($add_combos as $subset) {
		$combinations []= $subset;
	}
	return $combinations;
}