Union.scala

// From http://milessabin.com/blog/2011/06/09/scala-union-types-curry-howard/

type ∧[A, B] = A with B
type ¬[A] = A => Nothing
type ¬¬[A] = ¬[¬[A]]
type ∨[A, B] = ¬[¬[A] ∧ ¬[B]] // De Morgan equivalence
type <|[X, T] =  ¬¬[X] <:< T  // lift and check subtype

def size[T: ? <| (Int ∨ String)](t: T): Int =
  t match {
    case i: Int => i
    case s: String => s.length
  }

size("meow")