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// error with -Xunapply, (because of missing call to memberType?)
trait Gunk[a] {
type Seq
object Cons {
def unapply(s: Seq) = unapply_Cons(s)
}
def unapply_Cons(s: Any): Option[Tuple2[a, Seq]]
}
class Join[a] extends Gunk[a] {
type Seq = JoinSeq
abstract class JoinSeq
case class App(xs: Seq, ys: Seq) extends JoinSeq
def append(s1: Seq, s2: Seq): Seq = s1 // mock implementation
def unapply_Cons(s: Any) = s match {
case App(Cons(x, xs), ys) => Some(Pair(x, append(xs, ys)))
case _ => null
}
}
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