# annotations.ludic — the annotation-first style. A handler's query is an
# @Queries decorator instead of a clause, and the program lists the handlers it
# drives with @Handles. Both lower to the same code the older spellings did.

@Handles(Move)
program RPG2D {
  property Transform { x: int = 0, y: int = 0, scale: int = 1 }
  property Velocity  { dx: int = 0, dy: int = 0 }
  model Actor { Transform, Velocity }

  handler Spawn phase Start {
    spawn Actor { Transform { x: 0, scale: 2 }  Velocity { dx: 3, dy: 1 } }
    spawn Actor { Transform { x: 0, scale: 0 }  Velocity { dx: 9, dy: 9 } }
  }

  # Move every Actor whose scale is positive and that is actually moving. The
  # query lives in the annotation; each bound property is addressed by its own
  # name in the body (`Transform`, `Velocity`), and a constraint like
  # `Transform{scale > 0}` reads `scale` as a field of Transform.
  @Queries(these: [Transform{scale > 0}, Velocity{dx > 0 or dy > 0}], on: Actor)
  handler Move phase Update {
    Transform.x = Transform.x + Velocity.dx
    Transform.y = Transform.y + Velocity.dy
  }

  handler Report phase Render {
    for (t) in query [Transform] { print_int(t.x); print_int(t.y) }
    quit()
  }
}