Existential types

[phischu]

It would be great if we had existential types

type Packet {
   Wrap[E](x: E, E => E at {})
}

[b-studios]

Yes, this is somewhat related to #68 .

For the ml backend, this is difficult to support, though.

[jiribenes]

@Jonaskr8 ran into this issue recently when working on his thesis, wanting to have a List[forall A. Var[A]] which is also expressible as List[Var[_]] in Scala or possibly as List[SomeVar] where SomeVar is an existential wrapper -- type SomeVar { SomeVar[A](var: Var[A]) }.