Translation of Raul Raja's article `FP for the average Joe - I - ScalaZ Validation` for using cats library instead of scalaz. @see http://bit.ly/1UzKBEW

validation.scala

/**
  Translation of Raul Raja's article
  `FP for the average Joe - I - ScalaZ Validation` 
  for using cats library instead of scalaz.
  
  @see http://bit.ly/1UzKBEW
*/

package joe

object Validation_1 {

  def toInts(maybeInts: List[String]): List[Int] =
    maybeInts map (_.toInt)

}

object Validation_2 {

  import scala.util.Try

  def toInts(maybeInts: List[String]): Try[List[Int]] =
    Try(maybeInts map (_.toInt))

}

object Validation_3 {

  import cats.data.{ValidatedNel, Validated}
  import cats.std.list._

  def toInts(maybeInts: List[String]): ValidatedNel[Throwable, List[Int]] = {
    val validationList = maybeInts map { s =>
      Validated.catchNonFatal(s.toInt :: Nil).toValidatedNel
    }
    validationList reduce (_ combine _)
  }

}

object Validation_4 {

  import cats._
  import cats.implicits._
  import cats.data.{ValidatedNel, Validated}

  import scala.language.higherKinds

  def validate[F[_]: Foldable, A, B: Monoid]
      (in: F[A])
      (out: A => B): ValidatedNel[Throwable, B] =
    in foldMap (a => Validated.catchNonFatal(out(a)).toValidatedNel)

  def toInts(maybeInts: List[String]): ValidatedNel[Throwable, List[Int]] =
    validate(maybeInts)(_.toInt :: Nil)    

}