Functional Programming: A PragPub Anthology

Lazy Collections

Scala also provides lazy collections, which allow us to postpone the creation to just in time or on-demand. This allows us to express some algorithms or logic in very succinct manner. Let’s see how laziness can be useful.

The following code will help us determine if a given number is prime:

def isPrime(number : Int) = {
  val sqrtOfNumber = math.sqrt(number).toInt
  val hasFactorsOtherThan1AndItself =
    (2 to sqrtOfNumber).exists { i => number % i == 0 }
  number > 1 && !hasFactorsOtherThan1AndItself
}

Suppose we need to determine a list of prime numbers. We could express it like this:

//Won't work
def primes(number : Int) : List[Int] = {
  if(isPrime(number)) number :: primes(number ...