making scala stm look like haskell stm

gistfile1.scala

package util

import scalaz.effect.IO
import scalaz._
import Scalaz._
import scala.concurrent.stm.{ retry => stmRetry, _ }

object X {

  type STM[+A] = ReaderT[IO, InTxn, A]
  type TVar[A] = Ref[A]

  def readTVar[A](r: TVar[A]): STM[A] =
    Reader { implicit t: InTxn => r() }.lift[IO]

  def putTVar[A](r: TVar[A], a: A): STM[Unit] =
    Reader { implicit t: InTxn => r() = a }.lift[IO]

  val retry: STM[Nothing] =
    Reader { implicit t: InTxn => stmRetry }.lift[IO]

  def newTVar[A](a: A): IO[TVar[A]] =
    IO(Ref(a))

  def atomically[A](a: STM[A]): IO[A] =
    atomic(a.run)

}