ludic/examples/ecs/world_query.ludic

# world_query.ludic — EV2b reflection: iterate the world by property (replaces
# tests/mod_c/world_query.c). world_query_next(prop, from) returns the next live
# entity (>= from) that has the property, or -1 — so a mod walks all bearers of a
# component without knowing the models. Two Units (hp 50, 60) → count 2, sum 110.
program WorldQuery {
  property Health { hp: int = 0, max: int = 0 }
  model Unit { Health }
  @Public @OnSpawn(Unit) handler Init { Health.hp = Health.max }

  entry {
    spawn Unit { Health { max: 50 } }
    spawn Unit { Health { max: 60 } }
    let H  = world_prop_id("Health")
    let hp = world_field_id(H, "hp")
    var count = 0
    var sum   = 0
    var e = world_query_next(H, 0)
    while e >= 0 {
      count = count + 1
      sum = sum + world_get(e, H, hp)
      e = world_query_next(H, e + 1)
    }
    print(count)   # 2
    print(sum)     # 110
  }
}