Parameterized type tags

gistfile1.scala

import scalaz._
import Scalaz._
import java.lang.{Long => JLong}

object ParameterizedTags {
  trait Nanoseconds[A]
  
  type SampleDuration[A] = JLong @@ Nanoseconds[A]

  case class Bar(a: BarDuration)  
  type BarDuration = SampleDuration[Bar]

  case class Foo(a: FooDuration)  
  type FooDuration = SampleDuration[Foo]

  val f: FooDuration = Tag(1L)
  val b: BarDuration = Tag(1L)
  
    // does not compile
  // val ff: FooDuration = b

  implicit val JLongMonoid =
    new Monoid[JLong] {
      private val M = Monoid[Long]
      def zero: JLong = M.zero
      def append(f1: JLong, f2: => JLong): JLong =
        M.append(f1, f2)
    }

  implicit def DurationMonoid[A] =
    new Monoid[SampleDuration[A]] {
      private val M = Monoid[JLong]
      def zero: SampleDuration[A] = Tag(M.zero)
      def append(f1: SampleDuration[A], f2: => SampleDuration[A]): SampleDuration[A] =
        Tag(M.append(f1, f2))
    }

  //val m = Monoid[Long]
  val m = Monoid[FooDuration]

}