/**
* @param Collection $xs
* @param integer $result
* @param \Closure $f
* @return integer
*/
function iterateCollection(Collection $xs, $result, $f)
{
if (!$xs->isEmpty()) {
return iterateCollection($xs->tail(), $f($xs->head()) + $result, $f);
} else {
return $result;
}
}
public function testHeadTail()
{
$collection = new Collection([1, 2, 3, 4]);
self::assertEquals(1, $collection->head());
self::assertCount(3, $collection->tail());
}