ThiporKong

def tsort[A](edges: Traversable[(A, A)]): Iterable[A] = {
    @tailrec
    def tsort(toPreds: Map[A, Set[A]], done: Iterable[A]): Iterable[A] = {
        val (noPreds, hasPreds) = toPreds.partition { _._2.isEmpty }
        if (noPreds.isEmpty) {
            if (hasPreds.isEmpty) done else sys.error(hasPreds.toString)
        } else {
            val found = noPreds.map { _._1 }
            tsort(hasPreds.mapValues { _ -- found }, done ++ found)    
        }

ashee

// cycle will lazily cycle through values from the seq argument
def cycle[T](seq: Seq[T]) = Stream.continually(seq).flatten


scala> val c = cycle(List(1, 2, 3))
scala> c take 10 force
res24: scala.collection.immutable.Stream[Int] = Stream(1, 2, 3, 1, 2, 3, 1, 2, 3, 1)

jesperdj

// Mersenne Twister 19937
// Based on code from: http://www.math.sci.hiroshima-u.ac.jp/~m-mat/MT/emt.html
// Note: This implementation is not thread-safe!
final class MersenneTwister (seed: Int = 5489) {
  private val N = 624
  private val M = 397

  private val MatrixA = 0x9908b0dfL

  private val UpperMask = 0x80000000L