Give NonEmptyChain more presence

core/src/main/scala/cats/data/EitherT.scala

@@ -205,6 +205,8 @@ final case class EitherT[F[_], A, B](value: F[Either[A, B]]) {
   def toValidatedNel(implicit F: Functor[F]): F[ValidatedNel[A, B]] =
     F.map(value)(_.toValidatedNel)
 
+  def toValidatedNec(implicit F: Functor[F]): F[ValidatedNec[A, B]] = ???
+
   /** Run this value as a `[[Validated]]` against the function and convert it back to an `[[EitherT]]`.
    *
    * The [[Applicative]] instance for `EitherT` "fails fast" - it is often useful to "momentarily" have
@@ -274,6 +276,12 @@ final case class EitherT[F[_], A, B](value: F[Either[A, B]]) {
    */
   def toNestedValidatedNel(implicit F: Functor[F]): Nested[F, ValidatedNel[A, ?], B] =
     Nested[F, ValidatedNel[A, ?], B](F.map(value)(_.toValidatedNel))
+
+  /**
+   * Transform this `EitherT[F, A, B]` into a `[[Nested]][F, ValidatedNec[A, ?], B]`.
+   */
+  def toNestedValidatedNec(implicit F: Functor[F]): Nested[F, ValidatedNec[A, ?], B] =
+    Nested[F, ValidatedNec[A, ?], B](F.map(value)(_.toValidatedNec))
 }
 
 object EitherT extends EitherTInstances {

core/src/main/scala/cats/data/Validated.scala

@@ -314,7 +314,7 @@ sealed abstract class Validated[+E, +A] extends Product with Serializable {
   }
 }
 
-object Validated extends ValidatedInstances with ValidatedFunctions{
+object Validated extends ValidatedInstances with ValidatedFunctions with ValidatedFunctionsBinCompat0 {
   final case class Valid[+A](a: A) extends Validated[Nothing, A]
   final case class Invalid[+E](e: E) extends Validated[E, Nothing]
 
@@ -602,3 +602,38 @@ private[data] trait ValidatedFunctions {
   final def condNel[A, B](test: Boolean, b: => B, a: => A): ValidatedNel[A, B] =
     if (test) validNel(b) else invalidNel(a)
 }
+
+private[data] trait ValidatedFunctionsBinCompat0 {
+
+
+  /**
+   * Converts a `B` to a `ValidatedNec[A, B]`.
+   *
+   * For example:
+   * {{{
+   * scala> Validated.validNec[IllegalArgumentException, String]("Hello world")
+   * res0: ValidatedNec[IllegalArgumentException, String] = Valid(Hello world)
+   * }}}
+   */
+  def validNec[A, B](b: B): ValidatedNec[A, B] = Validated.Valid(b)
+
+
+
+  /**
+   * Converts an `A` to a `ValidatedNec[A, B]`.
+   *
+   * For example:
+   * {{{
+   * scala> Validated.invalidNec[IllegalArgumentException, String](new IllegalArgumentException("Argument is nonzero"))
+   * res0: ValidatedNec[IllegalArgumentException, String] = Invalid(Chain(java.lang.IllegalArgumentException: Argument is nonzero))
+   * }}}
+   */
+  def invalidNec[A, B](a: A): ValidatedNec[A, B] = Validated.Invalid(NonEmptyChain.one(a))
+
+  /**
+   * If the condition is satisfied, return the given `B` as valid NEC,
+   * otherwise return the given `A` as invalid NEC.
+   */
+  final def condNec[A, B](test: Boolean, b: => B, a: => A): ValidatedNec[A, B] =
+    if (test) validNec(b) else invalidNec(a)
+}

core/src/main/scala/cats/data/package.scala

@@ -5,6 +5,9 @@ package object data {
   type ValidatedNel[+E, +A] = Validated[NonEmptyList[E], A]
   type IorNel[+B, +A] = Ior[NonEmptyList[B], A]
   type EitherNel[+E, +A] = Either[NonEmptyList[E], A]
+  type ValidatedNec[+E, +A] = Validated[NonEmptyChain[E], A]
+  type IorNec[+B, +A] = Ior[NonEmptyChain[B], A]
+  type EitherNec[+E, +A] = Either[NonEmptyChain[E], A]
 
   def NonEmptyStream[A](head: A, tail: Stream[A] = Stream.empty): NonEmptyStream[A] =
     OneAnd(head, tail)

core/src/main/scala/cats/syntax/all.scala

@@ -72,3 +72,5 @@ trait AllSyntaxBinCompat1
 
 trait AllSyntaxBinCompat2
   extends ParallelTraverseSyntax
+    with EitherSyntaxBinCompat0
+    with ListSyntaxBinCompat0

core/src/main/scala/cats/syntax/either.scala

@@ -1,7 +1,8 @@
 package cats
 package syntax
 
-import cats.data.{EitherT, Ior, NonEmptyList, Validated, ValidatedNel}
+import cats.data._
+
 import scala.reflect.ClassTag
 import scala.util.{Failure, Success, Try}
 import EitherSyntax._
@@ -374,6 +375,49 @@ final class EitherIdOps[A](val obj: A) extends AnyVal {
 
 }
 
+trait EitherSyntaxBinCompat0 {
+  implicit final def catsSyntaxEitherBinCompat0[A, B](eab: Either[A, B]): EitherOpsBinCompat0[A, B] =
+    new EitherOpsBinCompat0(eab)
+
+  implicit final def catsSyntaxEitherIdBinCompat0[A](a: A): EitherIdOpsBinCompat0[A] =
+    new EitherIdOpsBinCompat0(a)
+}
+
+final class EitherIdOpsBinCompat0[A](val value: A) extends AnyVal {
+  /**
+   * Wrap a value to a left EitherNec
+   *
+   * For example:
+   * {{{
+   * scala> import cats.implicits._, cats.data.NonEmptyChain
+   * scala> "Err".leftNec[Int]
+   * res0: Either[NonEmptyChain[String], Int] = Left(Chain(Err))
+   * }}}
+   */
+  def leftNec[B]: Either[NonEmptyChain[A], B] = Left(NonEmptyChain.one(value))
+
+  /**
+   * Wrap a value to a right EitherNec
+   *
+   * For example:
+   * {{{
+   * scala> import cats.implicits._, cats.data.NonEmptyChain
+   * scala> 1.rightNec[String]
+   * res0: Either[NonEmptyChain[String], Int] = Right(1)
+   * }}}
+   */
+  def rightNec[B]: Either[NonEmptyChain[B], A] = Right(value)
+}
+
+final class EitherOpsBinCompat0[A, B](val value: Either[A, B]) extends AnyVal {
+  /** Returns a [[cats.data.ValidatedNec]] representation of this disjunction with the `Left` value
+   * as a single element on the `Invalid` side of the [[cats.data.NonEmptyList]]. */
+  def toValidatedNec[AA >: A]: ValidatedNec[AA, B] = value match {
+    case Left(a)  => Validated.invalidNec(a)
+    case Right(b) => Validated.valid(b)
+  }
+}
+
 /** Convenience methods to use `Either` syntax inside `Either` syntax definitions. */
 private[cats] object EitherUtil {
   def leftCast[A, B, C](right: Right[A, B]): Either[C, B] =

core/src/main/scala/cats/syntax/list.scala

@@ -2,7 +2,7 @@ package cats
 package syntax
 
 import scala.collection.immutable.SortedMap
-import cats.data.NonEmptyList
+import cats.data.{NonEmptyChain, NonEmptyList}
 
 trait ListSyntax {
   implicit final def catsSyntaxList[A](la: List[A]): ListOps[A] = new ListOps(la)
@@ -49,3 +49,30 @@ final class ListOps[A](val la: List[A]) extends AnyVal {
     toNel.fold(SortedMap.empty[B, NonEmptyList[A]])(_.groupBy(f))
   }
 }
+
+trait ListSyntaxBinCompat0 {
+  implicit final def catsSyntaxListBinCompat0[A](la: List[A]): ListOpsBinCompat0[A] = new ListOpsBinCompat0(la)
+}
+
+final class ListOpsBinCompat0[A](val la: List[A]) extends AnyVal {
+
+  /**
+   * Groups elements inside this `List` according to the `Order` of the keys
+   * produced by the given mapping function.
+   *
+   * {{{
+   * scala> import cats.data.NonEmptyChain
+   * scala> import scala.collection.immutable.SortedMap
+   * scala> import cats.implicits._
+   *
+   * scala> val list = List(12, -2, 3, -5)
+   *
+   * scala> list.groupByNec(_ >= 0)
+   * res0: SortedMap[Boolean, NonEmptyChain[Int]] = Map(false -> Chain(-2, -5), true -> Chain(12, 3))
+   * }}}
+   */
+  def groupByNec[B](f: A => B)(implicit B: Order[B]): SortedMap[B, NonEmptyChain[A]] = {
+    implicit val ordering = B.toOrdering
+    NonEmptyChain.fromSeq(la).fold(SortedMap.empty[B, NonEmptyChain[A]])(_.groupBy(f).toSortedMap)
+  }
+}

core/src/main/scala/cats/syntax/package.scala

@@ -23,15 +23,15 @@ package object syntax {
   object contravariant extends ContravariantSyntax
   object contravariantSemigroupal extends ContravariantSemigroupalSyntax
   object contravariantMonoidal extends ContravariantMonoidalSyntax
-  object either extends EitherSyntax
+  object either extends EitherSyntax with EitherSyntaxBinCompat0
   object eq extends EqSyntax
   object flatMap extends FlatMapSyntax
   object foldable extends FoldableSyntax
   object functor extends FunctorSyntax
   object group extends GroupSyntax
   object invariant extends InvariantSyntax
   object ior extends IorSyntax
-  object list extends ListSyntax
+  object list extends ListSyntax with ListSyntaxBinCompat0
   object monad extends MonadSyntax
   object monadError extends MonadErrorSyntax
   object monoid extends MonoidSyntax

tests/src/test/scala/cats/tests/EitherSuite.scala

@@ -223,6 +223,7 @@ class EitherSuite extends CatsSuite {
       x.isLeft should === (x.toList.isEmpty)
       x.isLeft should === (x.toValidated.isInvalid)
       x.isLeft should === (x.toValidatedNel.isInvalid)
+      x.isLeft should === (x.toValidatedNec.isInvalid)
       Option(x.isLeft) should === (x.toEitherT[Option].isLeft)
     }
   }

tests/src/test/scala/cats/tests/EitherTSuite.scala

@@ -159,6 +159,12 @@ class EitherTSuite extends CatsSuite {
     }
   }
 
+  test("toNestedValidatedNec") {
+    forAll { (eithert: EitherT[List, String, Int]) =>
+      eithert.toNestedValidatedNec.value should === (eithert.value.map(_.toValidatedNec))
+    }
+  }
+
   test("withValidated") {
     forAll { (eithert: EitherT[List, String, Int], f: String => Char, g: Int => Double) =>
       eithert.withValidated(_.bimap(f, g)) should === (eithert.bimap(f, g))

tests/src/test/scala/cats/tests/SyntaxSuite.scala

@@ -4,7 +4,7 @@ package tests
 import scala.collection.immutable.SortedSet
 import scala.collection.immutable.SortedMap
 import cats.arrow.Compose
-import cats.data.{Binested, Nested, NonEmptyList, NonEmptySet}
+import cats.data.{Binested, Nested, NonEmptyChain, NonEmptyList, NonEmptySet}
 import cats.instances.AllInstances
 import cats.syntax.{AllSyntax, AllSyntaxBinCompat}
 
@@ -377,5 +377,12 @@ object SyntaxSuite extends AllSyntaxBinCompat with AllInstances with AllSyntax {
     val grouped: SortedMap[B, NonEmptyList[A]] = list.groupByNel(f)
   }
 
+  def testNonEmptyChain[A, B: Order] : Unit = {
+    val f = mock[A => B]
+    val list = mock[List[A]]
+
+    val grouped: SortedMap[B, NonEmptyChain[A]] = list.groupByNec(f)
+  }
+
 }
 

tests/src/test/scala/cats/tests/ValidatedSuite.scala

@@ -280,6 +280,12 @@ class ValidatedSuite extends CatsSuite {
     }
   }
 
+  test("condNec consistent with Either.cond + toValidatedNec") {
+    forAll { (cond: Boolean, s: String, i: Int) =>
+      Validated.condNec(cond, s, i) should === (Either.cond(cond, s, i).toValidatedNec)
+    }
+  }
+
   test("liftTo consistent with direct to Option") {
     forAll { (v: Validated[Unit, Int]) =>
       v.liftTo[Option] shouldBe v.toOption