monad2.scala

def compute1(maybeFoo: Option[Foo]): Option[Int] =
  for {
    foo <- maybeFoo
    bar <- foo.bar
    baz <- bar.baz
  } yield baz.compute

// for compute2
import scalaz._
import Scalaz._ 

sealed trait Validation[E, A] {
  def map[B](f: A => B): Validation[E, B]
  def flatMap[B](f: A => Validation[E, B]): Validation[E, B]
  def liftFail[F](f: E => F): Validation[F, A] // unrelated to monads!
}

case class Success[E, A](a: A) extends Validation[E, A] {
  def map[B](f: A => B): Validation[E, B] = new Success(f(a))
  def flatMap[B](f: A => Validation[E, B]): Validation[E, B] = f(a)
  def liftFail[F](f: E => F): Validation[F, A] = new Success(a)
}

case class Failure[E, A](e: E) extends Validation[E, A] {
  def map[B](f: A => B): Validation[E, B] = new Failure(e)
  def flatMap[B](f: A => Validation[E, B]): Validation[E, B] = new Failure(e)
  def liftFail[F](f: E => F): Validation[F, A] = new Failure(f(e))
}

def compute2(foo: Foo): Validation[ComputeException, Int] =
  for {
    bar <- foo.bar.liftFail { new ComputeException(_) }
    baz <- bar.baz.liftFail { new ComputeException(_) }
    result <- baz.compute
  } yield result

Hi!
There is no liftFail method in Scalaz Validation today.. :(
How i can use this feature?