ZipperControl.scala

def tapRender[B: ToRefTree](value: B) = { render(value); value }

def zipperControl[A](zipper: Zipper[A])(implicit toRefTree: ToRefTree[Zipper[A]]): Unit = {
  Iterator
    .continually(Console.in.read())
    .takeWhile(_ != 'q')
    .filter(Set('w', 'a', 's', 'd'))
    .foldLeft(tapRender(zipper)) {
      case (z, 'w') ⇒ tapRender(z.tryMoveUp.orStay)
      case (z, 'a') ⇒ tapRender(z.tryMoveLeft.orStay)
      case (z, 's') ⇒ tapRender(z.tryMoveDownLeft.orStay)
      case (z, 'd') ⇒ tapRender(z.tryMoveRight.orStay)
    }
}