added new methods for Validation

zio-schema/shared/src/main/scala/zio/schema/validation/Bool.scala

@@ -4,6 +4,13 @@ sealed trait Bool[A] { self =>
   def &&(that: Bool[A]): Bool[A] = Bool.And(self, that)
   def ||(that: Bool[A]): Bool[A] = Bool.Or(self, that)
   def unary_! : Bool[A]          = Bool.Not(self)
+
+  def map[B](f: A => B, notCounter: Int = 0): Bool[B] = self match {
+    case Bool.And(left, right) => Bool.And(left.map(f, notCounter), right.map(f, notCounter))
+    case Bool.Or(left, right)  => Bool.Or(left.map(f, notCounter), right.map(f, notCounter))
+    case Bool.Leaf(value)      => Bool.Leaf(f(value))
+    case Bool.Not(value)       => Bool.Not(value.map(f, notCounter + 1))
+  }
 }
 
 object Bool {

zio-schema/shared/src/main/scala/zio/schema/validation/Predicate.scala

@@ -2,10 +2,11 @@ package zio.schema.validation
 
 import zio.Chunk
 
-sealed trait Predicate[A] {
+sealed trait Predicate[A] { self =>
   type Errors = Chunk[ValidationError]
   type Result = Either[Errors, Errors]
   def validate(value: A): Result
+  def premap[B](f: B => A): Predicate[B] = Predicate.Premap(Bool.Leaf(self), f)
 }
 
 object Predicate {
@@ -69,4 +70,27 @@ object Predicate {
   final case class True[A]() extends Predicate[A] { // A => True
     def validate(value: A): Result = Right(Chunk.empty)
   }
+
+  final case class Optional[A](pred: Bool[Predicate[A]], validNone: Boolean) extends Predicate[Option[A]] {
+
+    def validate(value: Option[A]): Result = value match {
+      case None =>
+        if (validNone) Right(Chunk(ValidationError.EqualToNone())) else Left(Chunk(ValidationError.EqualToNone()))
+      case Some(v) => Validation(pred).validate(v).map(_ => Chunk.empty)
+    }
+  }
+
+  final case class Premap[B, A](pred: Bool[Predicate[A]], f: (B => A)) extends Predicate[B] {
+    def validate(value: B): Result = Validation(pred).validate(f(value)).map(_ => Chunk.empty)
+  }
+
+  final case class Either[L, R](left: Bool[Predicate[L]], right: Bool[Predicate[R]])
+      extends Predicate[scala.util.Either[L, R]] {
+
+    def validate(value: scala.util.Either[L, R]): Result = value match {
+      case scala.util.Left(l)  => Validation(left).validate(l).map(_ => Chunk.empty)
+      case scala.util.Right(r) => Validation(right).validate(r).map(_ => Chunk.empty)
+    }
+  }
+
 }

zio-schema/shared/src/main/scala/zio/schema/validation/Validation.scala

@@ -7,6 +7,27 @@ final case class Validation[A](bool: Bool[Predicate[A]]) { self =>
   def ||(that: Validation[A]): Validation[A] = Validation(self.bool || that.bool)
   def unary_! : Validation[A]                = Validation(!self.bool)
 
+  /*
+    Returns a `Validation` for `Option[A]` applying current `Validation` if found value is `Some(_)` and accepts `None` depending on `validNone`.
+   */
+  def optional(validNone: Boolean = true): Validation[Option[A]] =
+    Validation(Bool.Leaf(Predicate.Optional(bool, validNone)))
+
+  /*
+    Returns a new `Validation` transforming a `B` value using `f` and then validating.
+   */
+  def premap[B](f: B => A): Validation[B] = Validation(bool.map(_.premap(f)))
+
+  /*
+    Returns a new `Validation` for `Either[B, A]`. With default `onLeft` fails on `Left` and applies current validation on `Right`.
+   */
+  def right[B](onLeft: Validation[B] = Validation.fail[B]): Validation[Either[B, A]] = Validation.either(onLeft, self)
+
+  /*
+    Returns a new `Validation` for `Either[A, B]`. With default `onRight` fails on `Right` and applies current validation on `Left`.
+   */
+  def left[B](onRight: Validation[B] = Validation.fail[B]): Validation[Either[A, B]] = Validation.either(self, onRight)
+
   def validate(value: A): Either[Chunk[ValidationError], Unit] = {
     type Errors = Chunk[ValidationError]
     type Result = Either[Errors, Errors]
@@ -76,4 +97,7 @@ object Validation extends Regexs with Time {
 
   def anyOf[A](vs: Validation[A]*): Validation[A]          = vs.foldLeft(fail[A])(_ || _)
   def anyOf[A](vl: Iterable[Validation[A]]): Validation[A] = anyOf(vl.toSeq: _*)
+
+  def either[L, R](left: Validation[L], right: Validation[R]): Validation[scala.util.Either[L, R]] =
+    Validation(Bool.Leaf(Predicate.Either(left.bool, right.bool)))
 }

zio-schema/shared/src/main/scala/zio/schema/validation/ValidationErrors.scala

@@ -26,7 +26,18 @@ object ValidationError {
     override def message: String =
       s"$value should be equal to $expected"
   }
-
+  final case class EqualToNone() extends ValidationError {
+    override def message: String =
+      s"Value should not be None"
+  }
+  final case class EqualToLeft[A](value: A) extends ValidationError {
+    override def message: String =
+      s"$value should not be Left"
+  }
+  final case class EqualToRight[A](value: A) extends ValidationError {
+    override def message: String =
+      s"$value should not be Right"
+  }
   final case class NotEqualTo[A](value: A, expected: A) extends ValidationError {
     override def message: String =
       s"$value should not be equal to $expected"

zio-schema/shared/src/test/scala/zio/schema/validation/ValidationSpec.scala

@@ -18,6 +18,47 @@ object ValidationSpec extends ZIOSpecDefault {
   import zio.schema.validation.ValidationSpec.Second._
 
   def spec: Spec[Environment with TestEnvironment with Scope, Any] = suite("ValidationSpec")(
+    test("Optional") {
+      val validationDefault = Validation.greaterThan(4).optional(true)
+      val validationTrue    = Validation.greaterThan(4).optional(true)
+      val validationFalse   = Validation.greaterThan(4).optional(false)
+
+      assertTrue(validationDefault.validate(Some(4)).isLeft) &&
+      assertTrue(validationDefault.validate(Some(5)).isRight) &&
+      assertTrue(validationDefault.validate(None).isRight) &&
+      assertTrue(validationTrue.validate(Some(4)).isLeft) &&
+      assertTrue(validationTrue.validate(Some(5)).isRight) &&
+      assertTrue(validationTrue.validate(None).isRight) &&
+      assertTrue(validationFalse.validate(Some(4)).isLeft) &&
+      assertTrue(validationFalse.validate(Some(5)).isRight) &&
+      assertTrue(validationFalse.validate(None).isLeft)
+
+    },
+    test("Premap") {
+      val validation = Validation.greaterThan(4).premap[Int](x => x - 10)
+
+      assertTrue(validation.validate(14).isLeft) &&
+      assertTrue(validation.validate(15).isRight)
+
+    },
+    test("Either") {
+      val validation      = Validation.greaterThan(4)
+      val validationLeft  = validation.left[String]()
+      val validationRight = validation.right[String]()
+      val validationBoth  = Validation.either(Validation.greaterThan(4), Validation.greaterThan(5))
+
+      assertTrue(validationLeft.validate(Left(4)).isLeft) &&
+      assertTrue(validationLeft.validate(Left(5)).isRight) &&
+      assertTrue(validationLeft.validate(Right("a")).isLeft) &&
+      assertTrue(validationRight.validate(Right(4)).isLeft) &&
+      assertTrue(validationRight.validate(Left("a")).isLeft) &&
+      assertTrue(validationRight.validate(Right(5)).isRight) &&
+      assertTrue(validationBoth.validate(Left(4)).isLeft) &&
+      assertTrue(validationBoth.validate(Left(5)).isRight) &&
+      assertTrue(validationBoth.validate(Right(5)).isLeft) &&
+      assertTrue(validationBoth.validate(Right(6)).isRight)
+
+    },
     test("Greater than") {
       val validation = Validation.greaterThan(4)