ValidationTraverseOps.scala

import scala.language.higherKinds
import scalaz.{Semigroup, Traverse, Validation}

object ValidationTraverseOps {
  implicit class ValidationTraverseOps[G[_], T](val gt: G[T]) extends AnyVal {
    def traverseRight[U, E : Semigroup](fun: T => Validation[E, U])(implicit traverseG: Traverse[G]): Validation[E, G[U]] = {
      traverseG.traverse[({type L[TT] = Validation[E, TT]})#L, T, U](gt)(fun)
    }
  }
  
  //sample
  import scalaz.syntax.validation._
  import scalaz.std.option._
  import scalaz.ValidationNel

  val opt: Option[Int] = Some(5)
  def validate(s: Int): ValidationNel[String, Int] = s.success.ensure("too much")(_ <= 2).toValidationNel
  
  val result: ValidationNel[String, Option[Int]] = opt.traverseRight(validate)
}

This is, in fact, the same as traverseU, except made concrete for the * -> * -> * kind, Validation in specific. We removed this syntactic class and replaced all usages with traverseU, which I recomment to anyone that might be, or want to be, using this.