powerset.scala

import scala.annotation.tailrec

val a = List(1, 2, 3, 4)

@tailrec
def powerset(current: List[List[Int]], given: List[Int]): List[List[Int]] = given match {
  case Nil => current
  case head :: tail => powerset(current ++ (current map {x => head::x}), tail)
}

for (i <- powerset(List(Nil), a)) {
  println(i)
}