Scala/Haskell has the same thing, and it's an amazing feature. The proper type is that of

    trait IndexedStateT[A, B, C]

Which signifies a typelevel state machine moving from state A to state B emitting a value of type C.

I can only speak for scala, but i'm assuming haskell has singleton and literal types as well. Meaning that code like this works great.

    object DoorOpen
    object DoorClosed
   
    class Door {
      def open: IndexedState[DoorClosed.type, DoorOpen.type, Unit]
      def close: IndexedState[DoorOpen.type, DoorClosed.type, Unit]
    }

   val d = Door()
   for {
      _ <- d.open() //works
      _ <- d.close() // works
      // _ <- d.close() //compile error
   }

By my understanding of the article, it uses the borrow/move state to implement the state transistion. Is this generalizable to arbitrary state machines, or only a simple 2-state one?