#### Overview of this book

Scala Functional Programming Patterns
Credits
Aknowledgement
www.PacktPub.com
Preface
Free Chapter
Grokking the Functional Way
Singletons, Factories, and Builders
Recursion and Chasing your Own Tail
Lazy Sequences – Being Lazy, Being Good
Taming Multiple Inheritance with Traits
Of Visitors and Chains of Responsibilities
Traversals – Mapping/Filtering/Folding/Reducing
Higher Order Functions
Actors and Message Passing
Index

## Recursive streams

We looked at recursion earlier. Recursive forms are defined in terms of themselves. For example, folders can have subfolders, which, in turn, can have subfolders themselves. Another example is recursive methods calling themselves.

We can use a similar form to define recursive streams. To define recursive streams, consider the following case:

```scala> lazy val r = Stream.cons(1, Stream.cons(2, Stream.empty))
r: Stream.Cons[Int] = <lazy>
scala> (r take 4) foreach {x => println(x)}
1
2
```

How is this useful? The second cons call can be recursive. (Note we don't need any var):

```scala> def s(n: Int):Stream[Int]  =
|   Stream.cons(n, s(n+1))  // 1
s: (n: Int)Stream[Int]
scala> lazy val q = s(0)
q: Stream[Int] = <lazy>
```

Here, we construct the lazy list by placing a recursive call to the method, `s`.

However, the following form is a succinct one:

```scala> def succ(n: Int):Stream[Int] = n #:: succ(n+1)
succ: (n: Int)Stream[Int]
scala> lazy val r...```