Succeeded
An ExitCase that signals successful completion.
Note that "successful" is from the type of view of the
MonadCancel type.
When combining such a type with EitherT or OptionT for
example, this exit condition might not signal a successful
outcome for the user, but it does for the purposes of the
bracket operation. <-- TODO still true?
trait Singleton
trait Product
trait Mirror
trait ExitCase
trait Serializable
trait Product
trait Equals
class Object
trait Matchable
class Any