build.sbt

libraryDependencies ++= Seq(
  "org.scalaz" %% "scalaz-core" % "7.1.0-M4"
)

scalaVersion := "2.10.3"

initialCommands in console := """
import scalaz._
import Scalaz._
import scalaz.std.scalaFuture._
import scala.concurrent.Future
import scala.concurrent.ExecutionContext.Implicits.global
"""

scalaz_validation_sample.scala

object Main {

  import scalaz._, Scalaz._

  case class Person(name: String, age: Int)

  type Error = String

  val parseName: String => ValidationNel[Error, String] = {
    case name if name.nonEmpty && name.forall(('a' to 'z').toSet) =>
      Success(name)
    case other =>
      "invalid name".failNel
  }

  val parseAge: String => ValidationNel[Error, Int] = { s =>
    util.Try(s.toInt).map{
      case n if n >= 0 => n.successNel[Error]
      case _ => "age must be positive".failNel[Int]
    }.getOrElse((s + " is not number").failNel)
  }

  def parsePerson(name: String, age: String): ValidationNel[Error, Person] =
    (parseName(name) |@| parseAge(age))(Person.apply)


  implicit val personEqual = Equal.equalA[Person]
  implicit val personShow = Show.showA[Person]


  def main(args: Array[String]){
    parsePerson("foo", "10") assert_=== Success(Person("foo", 10))

    parsePerson("foo bar", "10") assert_=== "invalid name".failNel[Person]

    parsePerson("foo bar", "aaa") assert_=== NonEmptyList("invalid name", "aaa is not number").fail[Person]

  }
}