Something weird I tried

Combinations.php

<?php
header('Content-Type: text/plain');

class Combinations {
    public static function GetIt($String) {
		echo '[n, s]'."\n";
		self::GetCombinations(str_split($String), 0, 0);
	}

	private static function GetCombinations($a, $n, $s) {
		// [a, s, d, f]
		$new = [$a[$n]];
		for($i = $s; $i < sizeof($a) + 1; $i++) {
			if($i == $n)
				continue;
			if(sizeof($new) != sizeof($a)) {
				if($i == sizeof($a))
					$i = 0;
				if($i == $n)
					continue;
				$new[] = $a[$i];
				echo $i;
			}
		}
		echo '['.$n.', '.$s.'] '.implode('', $new)."\n";
		if($s < sizeof($a))
			self::GetCombinations($a, $n, $s + 1);
	}
}

Combinations::GetIt('asdf');
/* Expected:
asdf
adfs
afsd
asfd
*/