scalaz and reify/reflect

gistfile1.scala

import util.continuations._
import scalaz._
import Scalaz._

def reify[M[_] : Monad, A](body: => A @cps[M[A]]): M[A] =
  reset{val result: A = body; implicitly[Monad[M]].pure[A](result)}

implicit def monad2reflect[M[_] : Monad, A](action: M[A]) = new {
  def reflect[B]: A @cps[M[B]] =
    shift{(k: A => M[B]) => implicitly[Monad[M]].bind(action, k)}
}

def guard[M[_], A](x: Boolean)(
  implicit m: Monad[M], z: Zero[M[Unit]]
): Unit @cps[M[A]] =
  if (x) m.pure[Unit](()).reflect[A] else z.zero.reflect[A]

//example
reify {
  type Result = Seq[Int]
  val nums = 0 to 9 toStream
  val nums1 = 1 to 9 toStream
  val S = nums1.reflect[Result]
  val E = nums.filterNot(S ==).reflect[Result]
  val N = nums.filterNot(Seq(S, E).contains).reflect[Result]
  val D = nums.filterNot(Seq(S, E, N).contains).reflect[Result]
  val M = nums1.filterNot(Seq(S, E, N, D).contains).reflect[Result]
  val O = nums.filterNot(Seq(S, E, N, D, M).contains).reflect[Result]
  val R = nums.filterNot(Seq(S, E, N, D, M, O).contains).reflect[Result]
  val Y = nums.filterNot(Seq(S, E, N, D, M, O, R).contains).reflect[Result]
  def toNum(nums: Seq[Int]) = nums.foldLeft(0)(_*10+_)
  guard[Stream, Result] {
    toNum(Seq(S, E, N, D)) + toNum(Seq(M, O, R, E)) ==
      toNum(Seq(M, O, N, E, Y))
  }
  Seq(S, E, N, D, M, O, R, E, M, O, N, E, Y)
}