Left-folds the elements of given range, that is, returns the result of evaluation of the chain expression:f(f(f(f(x 1, x 2), x 3), ...), x n), where x 1, x 2, ..., x n are elements of the range.. Informally, ranges::fold_left_first_with_iter behaves like std::accumulate 's overload that accepts a binary predicate, except that the * first is used internally as an initial element.