gistfile1.txt

trait Mutability[F[_]] {
  def init[A](a: A): F[Mutability.Var[F, A]]
}

object Mutability {
  trait Var[F[_], A] {
    def get: F[A]
    def put(a: A): F[Unit]
  }

  implicit val idMutableVar: Mutability[Id] = new Mutability[Id] {
    def init[A](a: A): Id[Var[Id, A]] = new Var[Id, A] {
      private var value: A = a
      def get: Id[A] = a
      def put(a: A): Id[Unit] = {
        value = a
      }
    }
  }

  implicit def syncMutableVar[F[_]: Sync]: Mutability[F] =
    new Mutability[F] {
      def init[A](a: A): F[Var[F, A]] = {
        for {
          ref <- Ref.of[F, A](a)
        } yield new Var[F, A] {
          def get: F[A] = ref.get
          def put(a: A): F[Unit] =
            ref.set(a)
        }
      }
    }
}