src/Zicht/Itertools/lib/Traits/AccumulateTrait.php
public function accumulate($closure = 'add')
    {
        if ($this instanceof \Iterator) {
            return new AccumulateIterator(
                $this,
                $closure instanceof \Closure ? $closure : reductions\get_reduction($closure)
            );
        }

        return null;
    }
public function accumulate($closure = 'add')
    {
        if ($this instanceof \Iterator) {
            return new AccumulateIterator(
                $this,
                $closure instanceof \Closure ? $closure : reductions\get_reduction($closure)
            );
        }

        return null;
    }
Returns an iterator that containing accumulated elements

If the optional $closure argument is supplied, it should be a string:
add, sub, mul, min, or max.  Or it can be a Closure taking two
arguments that will be used to instead of addition.

> iter\iterable([1,2,3,4,5])->accumulate()
1 3 6 10 15

> iter\iterable(['One', 'Two', 'Three'])->accumulate(function ($a, $b) { return $a . $b; })
'One' 'OneTwo' 'OneTwoThree'

@param string|\Closure $closure
@return null|AccumulateIterator