gistfile1.scala

scala> :pa
// Entering paste mode (ctrl-D to finish)

def subsets[A](as: List[A]): List[List[A]] = {
  def sub0(accum: List[List[A]], as: List[A]): List[List[A]] = 
    as match {
      case Nil => accum
      case a :: as => sub0(accum ++ accum.map(a :: _), as)
    }
  sub0(List(Nil), as)
}


// Exiting paste mode, now interpreting.

subsets: [A](as: List[A])List[List[A]]

scala> subsets(List(1, 2, 3, 4, 5)).filter(_.sum < 8)
res9: List[List[Int]] = List(List(), List(1), List(2), List(2, 1), List(3), List(3, 1), List(3, 2), List(3, 2, 1), List(4), List(4, 1), List(4, 2), List(4, 2, 1), List(4, 3), List(5), List(5, 1), List(5, 2))