anchor.diff:  type Car = {
       Make: string
       Model: string
  +    Mileage: int
   } with 
       static member make = 
           { Lens.Get = fun (x: Car) -> x.Make
  
positive.code: let LensChoice() = checkLens "choice" (Car.make .|. Car.model)
  
  [<Test>]
  let LensProduct() = checkLens "product" (Car.make *** Car.model)
negative.code: let stateMonadOperators() =
      let modify = 
          State.state {
              do! Editor.salary =! 1000
              do! Editor.salary += 100
          }
      let tom1 = modify tom |> snd
      Assert.AreEqual(1100, tom1.Salary)
  