Continuations and for comprehensions — what's the incompatibility?

Question

I am new to Scala and trying to wrap my head around continuations I'm trying to reproduce the yield return C# statement.

Following this post, I have written the following code :

package com.company.scalatest

import scala.util.continuations._;

object GenTest {

  val gen = new Generator[Int] {
    def produce = {
      yieldValue(1)
      yieldValue(2)
      yieldValue(3)
      yieldValue(42)
    }
  }
  // Does not compile :(

  //  val gen2 = new Generator[Int] {
  //    def produce = {
  //      var ints = List(1, 2, 3, 42);
  //
  //      ints.foreach((theInt) => yieldValue(theInt));
  //    }
  //  }

  // But this works?
  val gen3 = new Generator[Int] {
    def produce = {
      var ints = List(1, 2, 3, 42);
      var i = 0;
      while (i < ints.length) {
        yieldValue(ints(i));
        i = i + 1;
      }
    }
  }

  def main(args: Array[String]): Unit = {
    gen.foreach(println);
    //    gen2.foreach(println);
    gen3.foreach(println);
  }
}

abstract class Generator[E] {

  var loopFn: (E => Unit) = null

  def produce(): Unit @cps[Unit]

  def foreach(f: => (E => Unit)): Unit = {
    loopFn = f
    reset[Unit, Unit](produce)
  }

  def yieldValue(value: E) =
    shift { genK: (Unit => Unit) =>
      loopFn(value)
      genK(())
      ()
    }
}

As you can see, gen2 is commented out as it does not compile. Since I can easily iterate over the content of a list using a while loop (see gen3), I expected the foreach loop to work just as well.

The compilation error is the following :

no type parameters for method foreach: (f: Int => B)Unit exist so that 
it can be applied to arguments (Int => Unit @scala.util.continuations.cpsParam[Unit,Unit])  
 --- because --- 
argument expression's type is not compatible with formal parameter type;  
found   : Int => Unit @scala.util.continuations.cpsParam[Unit,Unit]  
required: Int => ?B 

Why do I get this error and is there a way to work around this with something cleaner than a while loop?

Thank you