record Item {
  k = 0
}
state items: list of Item
input fill = message { k: u32 }
input burst = message { step: u32 }
output out = message { k: u32 }
on fill {
  items.append(Item { k: fill.k })
}
on burst {
  for i in items {
    send out { k: i.k + burst.step }
  }
}
view count = count(i in items where i.k > 0)