SafeBool

   sealed trait Enabled extends SafeBool[Enabled] {
     override final def companion = Enabled
   }

   case object Enabled extends Enabled with SafeBool.Object[Enabled] {
     override def positive = Enabled
     override def negative = Disabled
   }

   case object Disabled extends Enabled

   sealed abstract class Permission extends SafeBool.WithBoolOps[Permission] {
     override final def companion = Permission
   }

   case object Allow extends Permission
   case object Deny extends Permission

   object Permission extends SafeBool.Object[Permission] {
     override def positive = Allow
     override def negative = Deny
   }