list extensions

//some nice but perhaps not so useful list operations

object ListOps {
//translated to Scala: http://www.haskell.org/pipermail/libraries/2010-July/013842.html
  def select[T](l: List[T]): List[(T, List[T])] = l match {
    case Nil => Nil
    case x::xs => (x, xs) :: (for {(y, ys) <- select(xs)} yield (y, x::ys))
  }

  def separate[T](l: List[T]): List[(List[T], T, List[T])] = l match {
    case Nil => Nil
    case x::xs => (Nil, x, xs) :: (for {(us, y, ys) <- separate(xs)} yield (x::us, y, ys))
  }

//http://stackoverflow.com/questions/2243812/functional-programming-implementing-scan-prefix-sum-using-fold
//'This, of course, is a horrible way to express scan but it is a fun exercise of jamming a square peg into a round hole'
//scanLeft does exactly the same thing, but anyway:
  def prefixSum(l:List[Int]) = l.foldLeft(List(0)){(l,e) => l ::: List(e + l.last)} 

}