Unique

A typeclass which is a source of unique tokens via unique

trait Unique[F[_]] {
  def unique: F[Unique.Token]
}

unique is guaranteed to produce a distinct value every time it is evaluated

val token: F[Unique.Token] = Unique[F].unique
(token, token).mapN { (x, y) => x === y } <-> Monad[F].pure(false)

Both Sync[F] and Spawn[F] extend Unique[F] as both typeclasses trivially have the ability to create unique values via delay(new Unique.Token()) and start respectively (fibers are always unique).