MathIterators { static InfiniteIterator<Long> faculty() { return new InfiniteIterator<Long>() { private int counter = 0; private long nextValue = 1; @Override public Long next() { if (nextValue < 0) { throw new NoSuchElementException(); } long result = nextValue; nextValue *= ++counter; return result; } }; } private  MathIterators(); static Comparator<Double> weakDoubleComparator(double epsilon); static UnaryOperator<Double> increment(Double delta); static UnaryOperator<Double> times(Double factor); static InfiniteIterator<Double> random(); static InfiniteIterator<Double> arithmeticSeries(double start, double delta); static InfiniteIterator<Double> geometricSeries(double start, double factor); static ImmutableIterator<Double> exp(); static ImmutableIterator<Double> sin(); static ImmutableIterator<Double> cos(); static ImmutableIterator<Double> add(Iterator<Double> s, double inc); @SuppressWarnings("unchecked") static Iterator<Double> inc(Iterator<Double> s, double inc); static ImmutableIterator<Double> add(Iterator<Double> s, Iterator<Double> t); static ImmutableIterator<Double> multiply(Iterator<Double> s, double factor); static ImmutableIterator<Double> multiply(Iterator<Double> s, Iterator<Double> t); static ImmutableIterator<Double> square(Iterator<Double> t); static InfiniteIterator<Double> inverse(Iterator<Double> t); static ImmutableIterator<Double> divide(Iterator<Double> s, Iterator<Double> t); static UnaryOperator<Double> polynom(Iterator<Double> t, int dim); static UnaryOperator<Double> polynom(Iterator<Double> t); static Iterator<Double> compose(Iterator<Double> t, Iterator<Double> s, int dim); static Iterator<Double> compose(Iterator<Double> t, Iterator<Double> s);  }
@Test public void testFaculty() { Iterator<Long> f7 = limit(faculty(), 7); BinaryOperator<Long> acc = (a, b) -> a + b; long sum = reduce(f7, acc); assertEquals(874, sum); }