gistfile1.scala

case class Position(x: Double, y: Double)

case class Bullet(position: Position, direction: Double)
case class Enemy(position: Position, health: Short)

var bullets = List[Bullet].empty
var enemies = List[Enemy].empty

def update() = {
  bullets =
    bullets.map(_.copy(position = /* magic to move it in its direction */))

  (hittingBullets, nonHittingBullets) =
    bullets.filter(_.position distanceTo enemy.position < 2)
  enemies =
    enemies
    .map { enemy => enemy.copy(health = enemy.health - hittingBullets.size) }
    .filter(_.health > 0)
  bullets = nonHittingBullets
}