I found this code interesting (not sarcasm) in demo/boiling.ml:
  let increase_level t =
    let level =
      match t.level with
      | No_Fire -> One_Fire
      | One_Fire -> Two_Fires
      | Two_Fires -> Three_Fires
      | Three_Fires -> Three_Fires
    in
    { t with level }
  ;;
  let decrease_level t =
    let level =
      match t.level with
      | No_Fire -> No_Fire
      | One_Fire -> No_Fire
      | Two_Fires -> One_Fire
      | Three_Fires -> Two_Fires
    in
    { t with level }
  ;; replies(1):