gistfile1.txt

scala> class Foo
defined class Foo

scala> val l = List(1,2,3)
l: List[Int] = List(1, 2, 3)

scala> def f(i: Int): Option[Int] = if (i % 2 == 0) Some(i) else None
f: (i: Int)Option[Int]

scala> l.map(f)
res0: List[Option[Int]] = List(None, Some(2), None)

scala> l.flatMap(f)
res1: List[Int] = List(2)

scala> def f[T <: Foo](i: T): Option[T] = ???
f: [T <: Foo](i: T)Option[T]

scala> l.flatMap(f)
<console>:11: error: polymorphic expression cannot be instantiated to expected type;
 found   : [T <: Foo]T => Option[T]
 required: Int => scala.collection.GenTraversableOnce[?]
              l.flatMap(f)
                        ^