My first scala experiment -- The Sieve of Eratosthenes

sieve.scala

/*
Whenever I start learning a language, the first program I try 
to write is an implementation of The Sieve of Eratosthenes. 
It requires you to work with lists, which I think is 
very important for any language.

This is my first stab of the Sieve in Scala.

*/


def sieve(total : Int): List[Int] = {

   var primes : List[Int] = List()
   var composites : Set[Int] = Set()
   for (i <- 2 until total+1) {

     if (! composites.contains(i)) {
       primes::=i
       
       composites = composites ++ Range(i+i,total+1,i).toSet

     }

   }
  primes.sorted

}

After doing some of the koans in Scala Koans, I fixed it up to be more precise and, perhaps, even faster