First cut at attempting to support CPS plugin and collections.

SuspendableProxy.scala

import collection.generic.CanBuildFrom
import util.continuations._

class SuspendableProxy[+T, +Repr <: Iterable[T]](xs: Repr)(implicit cbf : CanBuildFrom[Repr, T, Repr]) {
  private[this] def newBuilder = cbf()

  def foreach[A](body: T => Unit @cps[A]): Unit @cps[A] = {
    val it = xs.iterator
    while (it.hasNext) {
      body(it.next)
    }
  }
  def map[B, A, To](f : T => B @cps[A])(implicit bf : CanBuildFrom[Repr, B, To]) : To @cps[A] = {
    val b = bf()
    b.sizeHint(xs)
    val it = xs.iterator
    while (it.hasNext) {
      b += f(it.next)
    }
    b.result
  }
  def filter[A](f : T => Boolean) : Repr @cps[A] = {
    val it = xs.iterator
    val b = newBuilder
    b.sizeHint(xs)
    while (it.hasNext) {
      val elem = it.next
      if (f(elem))
        b += elem
    }
    b.result
  }

  def flatMap[B, A, To](f : T => Iterable[B] @cps[A])(implicit bf : CanBuildFrom[Repr, B, To]) : To @cps[A] = {
    val it = xs.iterator
    val b = bf()
    b.sizeHint(xs)
    while (it.hasNext) {
      b ++= f(it.next)
    }
    b.result
  }
}