13.13. Streams A3

In the preceding sections, you saw that an iterator is a “lazy” alternative to a collection. You get the elements as you need them. If you don’t need any more elements, you don’t pay for the expense of computing the remaining ones.

However, iterators are fragile. Each call to next mutates the iterator. Streams offer an immutable alternative. A stream is an immutable list in which the tail is computed lazily—that is, only when you ask for it.