package monocle.law
import monocle.Traversal
import org.scalacheck.Prop._
import org.scalacheck.{Arbitrary, Properties}
import scalaz.Equal
import scalaz.Id._
import scalaz.syntax.equal._
import scalaz.std.list._
import scalaz.std.option._
object TraversalLaws {
def apply[S: Arbitrary: Equal, A: Arbitrary: Equal](traversal: Traversal[S, A]) = new Properties("Traversal") {
property("you get what you set") = forAll { (s: S, a: A) =>
traversal.getAll(traversal.set(a)(s)) === traversal.getAll(s).map(_ => a)
}
property("set is idempotent") = forAll { (s: S, a: A) =>
traversal.set(a)(traversal.set(a)(s)) === traversal.set(a)(s)
}
property("modifyF preserves the structure") = forAll { s: S =>
traversal.modifyF[Id](id.point[A](_))(s) === s
}
property("modify preserves the structure") = forAll { s: S =>
traversal.modify(identity)(s) === s
}
property("headMaybe returns the first element of getAll (if getAll is finite)") = forAll { s: S =>
traversal.headOption(s) === traversal.getAll(s).headOption
}
}
}