Example of the inability of Store to form a Representable (yet is itself a sum of representables)

StoreRepresentable.scala

// Unable to implement `tabulate` without a value to provide as the index
implicit def representableForStore[S]: Representable.Aux[[A] =>> Store[S, A], S] =
  new Representable[[A] =>> Store[S, A]]:
    override type Representation = S
    override val F: Functor[[A] =>> Store[S, A]] = Functor[[A] =>> Store[S, A]]
    override def tabulate[A](f: S => A): Store[S, A] = ???
    override def index[A](f: Store[S, A]): S => A = (s: S) => f.peek(s)