Lazy prime numbers in Scala

	def primes : Stream[Int] = {
	def findNextPrime(primes: List[Int])={
	var i = primes.head+1
	while(primes.exists(x => i % x == 0)){i+=1}
	i
	}
	def prim(primes:List[Int]): Stream[Int] = primes match{
	case Nil => 1 #:: 2 #:: prim(List(2))
	case _ => {
	val next = findNextPrime(primes)
	next #:: prim(next::primes)
	}
	}
	prim(Nil)
	}

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The key to understanding this example is the #:: operator. It is very similar to :: for collections. The difference is that it doesn't evaluate the right hand side argument immediately. Instead it keeps it's reference as a function and evaluates it only when needed. The evaluation is deferred until the actual element is needed.