An enumeratee which takes every Nth element and discards the rest

gistfile1.scala

def takeEveryNth[E, F[_]:Monad](n: Int): EnumerateeT[E, E, F] =
  new EnumerateeT[E, E, F] {
    def apply[A] = {
      def loop(m: Int) = step(m) andThen cont[E, F, StepT[E, F, A]]
      def step(m: Int): (Input[E] => IterateeT[E, F, A]) => (Input[E] => IterateeT[E, F, StepT[E, F, A]]) = {
        k => in => in(
          empty = cont(step(m)(k)),
          eof   = done(scont(k), in),
          el    = e => if (m == n) k(in) >>== doneOr(loop(1))
                       else cont(step(m+1)(k))
        )
      }

      doneOr(loop(1))
    }
  }