scala> import scala.util.{Success, Failure}
import scala.util.{Success, Failure}

scala> def f1(b: Boolean) = if (b) Left(1) else Right(2)
f1: (b: Boolean)scala.util.Either[Int,Int]

scala> def f2(b: Boolean) = if (b) Nil else 1 :: Nil
f2: (b: Boolean)List[Int]

scala> def f3(b: Boolean) = if (b) Stream.Empty else new Stream.Cons(1, Stream.Empty)
f3: (b: Boolean)scala.collection.immutable.Stream[Int]

scala> def f4(b: Boolean) = if (b) Success(1) else Failure(new Exception(""))
f4: (b: Boolean)scala.util.Try[Int]

scala> :quit