gistfile1.scala

import language.higherKinds

import java.sql.Connection
import scalaz.{ Monad, StateT, Functor, State }
import scalaz.State._
import scalaz.MonadState._
import scalaz.std.tuple._
import scalaz.syntax.monad._
import scalaz.syntax.std.tuple._
import scalaz.effect.IO
import scalaz.effect.IO._

object Jed {

  class ConnectionWrapper(c: Connection) {
    def setAutoCommit(autoCommit: Boolean): IO[Unit] = IO(c.setAutoCommit(autoCommit))
    def getAutoCommit: IO[Boolean] = IO(c.getAutoCommit)
  }

  // State[Connection,A] becomes StateT[IO,ConnectionWrapper,A]
  def action: StateT[IO, ConnectionWrapper, Boolean] =
    for {
      w <- initT[IO, ConnectionWrapper]
      c <- liftM(w.getAutoCommit)
    } yield c

  val conn: Connection = ???

  val ioAction = action.eval(new ConnectionWrapper(conn))
  val result = ioAction.unsafePerformIO

  
  // Some combinators and lifted operations for StateT
  def lift[M[+_]: Monad, S, A](f: State[S, A]) = StateT[M, S, A](f(_).pure[M])
  def liftM[M[+_]: Functor, S, A](f: M[A]) = StateT[M, S, A](s => f.map((s, _)))
  def initT[M[+_]: Monad, S] = lift[M, S, S](init[S])
  def modifyT[M[+_]: Monad, S](f: S => S) = lift[M, S, Unit](modify[S](f))
  def putT[M[+_]: Monad, S](s: S) = lift[M, S, Unit](put(s))
  def getsT[M[+_]: Monad, S, A](f: S => A) = lift[M, S, A](gets(f))

}