class Object
  fun fac_case(0): U64 => 1
  fun fac_case(n: U64): U64 ? => n * (fac_case(n - 1) as U64)
actor Main
  new create(env: Env) =>
    let x: U64 = try
      (Object.fac_case(-7) as U64)
    else
      env.out.print("Error")
      U64(0)
    end
    env.out.print(x.string())