Fibonacci

Fib.scala

def fib: Stream[Long] = {
    def tail(h: Long, n: Long): Stream[Long] = h #:: tail(n, h + n)
    tail(0, 1)
}

Stream.scala

//from scala.collection.immutable.Stream  http://www.scala-lang.org/api/current/index.html#scala.collection.immutable.Stream

import scala.math.BigInt
object Main extends App {

  val fibs: Stream[BigInt] = BigInt(0) #:: BigInt(1) #:: fibs.zip(fibs.tail).map { n => n._1 + n._2 }

  fibs take 5 foreach println
}