yeld in php (for arrays only)

yeld.php

<?php

namespace core\utils;

/**
 * Loops over an array, calls expression on each its element and collects results into new array.
 * @param mixed $array
 * @param callback $expression Expression function taking $key and $value parameters.
 * @return array
 */
function yeld($array, $expression)
{
	$result = array();
	foreach($array as $key => $value)
		$result[$key] = $expression($key, $value);
	return $result;
}

/**
 * Joins all elements of $array with applying formatter and using separator string.
 * @param mixed $array
 * @param callback $formatter
 * @param string $separator
 * @return string
 */
function joinFormatted($array, $separator, $formatter)
{
	return implode($separator, yeld($array, function($key, $value)use($formatter) { return $formatter($key, $value); }));
}