"Entity component system" with type classes

Entites.scala

                                         
case class Map(
  // in real code use something that has better copy characteristics like some tree
  walls: List[Wall],
  boundaries: MapBoundaries)

case class World(
  player: PlayerCharacter, 
  map: Map,
  enemies: List[Enemy])

case class BoundingBox(x: Int, y: Int, width: Int, height: Int)

trait HasBoundingBox[T] {
  def bbox(t: T): BoundingBox
}

trait Movable[T] {
  def move(t: T, dx: Int, dy: Int): T 
}

trait PlayerOwned[T] {
  def react(t: T, input: PlayerInput): T
}

trait Renderable[T] {
  def render(t: T): Unit // or IO[Unit] if you want to
}

trait AiControlled[T] {
  def takeAction(t: T): T
}

case class PlayerCharacter(x: Int, y: Int)
object PlayerCharacter extends PlayerCharacterInstances

trait PlayerCharacterInstances {
  val PlayerSize = 10

  implicit val instance = new HasBoundingBox[Player] with Movable[Player] with PlayerOwned[Player] with Renderable[Player] {
    override def bbox(player: Player): BoundingBox = 
      BoundingBox(player.x - (PlayerSize / 2), player.y - (PlayerSize/ 2), PlayerSize, PlayerSize)

    override def move(player: Player, dx: Int, dy: Int): Player = {
      // for more complicated objects and logics look at lenses / monocle project
      Player.copy(x = x + dx, y = y + dy)
    }

    override def render(player: Player): Unit = {
      println(s"rendering: ${player}")
    }

    override def react(t: T, input: PlayerInput)
  }
}

case class Wall(x1: Int, y1: Int, x2: Int, y2: Int)

object Wall extends WallInstances

trait WallInstances {
  implicit val instance = new HasBoundingBox[Wall] with Movable[Wall] with Renderable[Wall] {
    // blah
  }
}

case class MapBoundaries(path: Path)
object MapBoundaries extends MapBoundariesInstances

trait MapBoundariesInstances {
  implicit val instance = new HasBoundingBox[Wall] {
    // blah
  }
}

case class Enemy(x: Int, y: Int, hp: Int)

object Enemy extends EnemyInstances

trait EnemyInstances {
  implicit val instance = new HasBoundingBox[Enemy] with Movable[Enemy] with AiControlled[Enemy] with Renderable[Enemy] {
    // blah
  }
}