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trait Zero
trait Succ[N]
trait ZipWith[N, S] {
type T
val x: T = sys.error("")
}
object ZipWith {
implicit def ZeroZipWith[S] = new ZipWith[Zero, S] {
type T = Stream[S]
}
implicit def SuccZipWith[N, S, R](implicit zWith : ZipWith[N, R]) = new ZipWith[Succ[N], S => R] {
type T = Stream[S] => zWith.T // dependent types replace the associated types functionality
}
// can't use implicitly[ZipWith[Succ[Succ[Zero]], Int => String => Boolean]],
// since that will chop of the {type T = ... } refinement in adapt (pt = ZipWith[Succ[Succ[Zero]], Int => String => Boolean])
// this works
// def zipWith(implicit zw: ZipWith[Succ[Succ[Zero]], Int => String => Boolean]): zw.T = zw.x
// thus, I present ?: implicitly on steroids!
def ?[T <: AnyRef](implicit w: T): w.type = w
type _2 = Succ[Succ[Zero]]
val zw = ?[ZipWith[_2, Int => String => Boolean]].x // : Stream[Int] => Stream[String] => Stream[Boolean]
// val zw = implicitly[ZipWith[Succ[Succ[Zero]], Int => String => Boolean]{type T = Stream[Int] => Stream[String] => Stream[Boolean]}].x
}
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