Custom Stream

Stream

import scala.annotation.tailrec


/**
  * Created by i.dey on 3/12/17.
  */
trait Stream[+T] {
  def isEmpty : Boolean
  def head : T
  def tail : Stream[T]

  @tailrec
  final def apply(n:Int): T = {
    if(isEmpty)
      throw new NoSuchElementException
    else if(n==0){
      head
    }else{
      tail.apply(n-1)
    }
  }
}

object EmptyStream extends Stream[Nothing]{
  override def isEmpty: Boolean = true
  override def head: Nothing = throw new NoSuchElementException
  override def tail: Stream[Nothing] = throw new NoSuchElementException
}


class ConStream[T](hd:T, tl: => Stream[T]) extends Stream[T]{
  override def isEmpty: Boolean = false
  override def head: T = hd
  lazy val tail: Stream[T] = tl
}

object Stream{
  def apply[T](lo:T, high: T)(greater:(T,T)=>Boolean, f:(T)=>T):Stream[T] = {
    if(greater(lo,high)){
      EmptyStream
    }else{
      new ConStream[T](lo,apply(f(lo),high)(greater,f))
    }
  }
  def apply[T](stream:Stream[T])(p:(T)=>Boolean): Stream[T] ={
    if(stream.isEmpty)
      EmptyStream
    else
    if(p(stream.head))
      new ConStream[T](stream.head, apply(stream.tail)(p))
    else
      apply(stream.tail)(p)
  }
}