Ds\Sequence::reduce() function can reduce the sequence to a single value using a callback function.
public abstract mixed Ds\Sequence::reduce( callable $callback [, mixed $initial ] )
Ds\Sequence::reduce() function can return the value of final callback.
<?php $seq = new \Ds\Vector([1, 2, 3]); $callback = function($carry, $value) { return $carry * $value; }; var_dump($seq->reduce($callback, 5)); ?>
<?php $seq = new \Ds\Vector([1, 2, 3]); var_dump($seq->reduce(function($carry, $value) { return $carry + $value + 5; })); ?>