/**
* reduceLeft - ReduceLeft is like reduce, but it is used for combining values into values of the same type. This is perfect for things like
* summing values, concatenating strings, union arrays, etc.
*
* @param callable $fn($prevValue, $currentValue, $currentKey) -- The $fn predicate is a function(T $prevValue, T $currentValue) that returns type T|null.
* @return mixed
*/
public function reduceLeft($fn)
{
return IterationTraits::reduceLeft($this, $fn);
}
