Derive MonoidK hierarchy (#342)

core/src/main/scala-3.0.0-RC3/cats/derived/all.scala

@@ -4,13 +4,16 @@ object all extends
   CommutativeMonoidDerivation,
   CommutativeSemigroupDerivation,
   EmptyDerivation,
+  EmptyKDerivation,
   EqDerivation,
   FoldableDerivation,
   FunctorDerivation,
   HashDerivation,
   MonoidDerivation,
+  MonoidKDerivation,
   OrderDerivation,
   PartialOrderDerivation,
   SemigroupDerivation,
+  SemigroupKDerivation,
   ShowDerivation,
   TraverseDerivation

core/src/main/scala-3.0.0-RC3/cats/derived/emptyk.scala

@@ -0,0 +1,19 @@
+package cats.derived
+
+import alleycats.{Empty, EmptyK}
+import shapeless3.deriving.K1
+
+object emptyk extends EmptyKDerivation
+
+trait ProductEmptyK[T[x[_]] <: EmptyK[x], F[_]](
+  using inst: K1.ProductInstances[T, F]
+) extends EmptyK[F]:
+  def empty[A]: F[A] = inst.construct([t[_]] => (emp: T[t]) => emp.empty[A])
+
+trait EmptyKDerivation:
+  extension (E: EmptyK.type)
+    inline def derived[F[_]](using gen: K1.ProductGeneric[F]): EmptyK[F] =
+      new ProductEmptyK[EmptyK, F]{}
+
+  given [X](using X: Empty[X]): EmptyK[Const[X]] with
+    def empty[A]: Const[X][A] = X.empty

core/src/main/scala-3.0.0-RC3/cats/derived/functor.scala

@@ -22,4 +22,4 @@ trait FunctorDerivation:
     new ProductFunctor[Functor, F]{}
 
   given [X]: Functor[Const[X]] with
-      def map[A, B](fa: Const[X][A])(f: A => B): Const[X][B] = fa
+    def map[A, B](fa: Const[X][A])(f: A => B): Const[X][B] = fa

core/src/main/scala-3.0.0-RC3/cats/derived/monoidk.scala

@@ -0,0 +1,20 @@
+package cats.derived
+
+import cats.{Monoid, MonoidK}
+import shapeless3.deriving.K1
+
+object monoidk extends MonoidKDerivation
+
+trait ProductMonoidK[T[x[_]] <: MonoidK[x], F[_]](using inst: K1.ProductInstances[T, F])
+  extends ProductSemigroupK[T, F], MonoidK[F]:
+    def empty[A]: F[A] = inst.construct([t[_]] => (emp: T[t]) => emp.empty[A])
+
+trait MonoidKDerivation:
+  extension (F: MonoidK.type)
+    inline def derived[F[_]](using gen: K1.Generic[F]): MonoidK[F] = ???
+
+  given [X](using X: Monoid[X]): MonoidK[Const[X]] with
+    def empty[A]: Const[X][A] = X.empty
+
+    def combineK[A](x: Const[X][A], y: Const[X][A]): Const[X][A] =
+      X.combine(x, y)

core/src/main/scala-3.0.0-RC3/cats/derived/semigroupk.scala

@@ -0,0 +1,21 @@
+package cats.derived
+
+import cats.{Semigroup, SemigroupK}
+import shapeless3.deriving.K1
+
+object semigroupk extends SemigroupKDerivation
+
+trait ProductSemigroupK[T[x[_]] <: SemigroupK[x], F[_]](using inst: K1.ProductInstances[T, F])
+  extends SemigroupK[F]:
+    def combineK[A](x: F[A], y: F[A]): F[A] = inst.map2[A, A, A](x,y)(
+      [t[_]] => (smgrpk: T[t], t0: t[A], t1: t[A]) => smgrpk.combineK(t0, t1)
+    )
+
+trait SemigroupKDerivation:
+  extension (F: SemigroupK.type)
+    inline def derived[F[_]](using gen: K1.ProductGeneric[F]): SemigroupK[F] =
+      new ProductSemigroupK[SemigroupK, F]{}
+
+  given [X](using X: Semigroup[X]): SemigroupK[Const[X]] with
+    def combineK[A](x: Const[X][A], y: Const[X][A]): Const[X][A] =
+      X.combine(x, y)

core/src/test/scala-3.0.0-RC3/cats/derived/EmptyKTests.scala

@@ -0,0 +1,11 @@
+package cats.derived
+
+import alleycats._
+import alleycats.std.all._
+import cats._
+import cats.derived.all._
+import cats.derived.all.given
+
+class EmptyKTests { //
+  case class Foo[A](i: String, l: List[A]) derives EmptyK
+}

core/src/test/scala-3.0.0-RC3/cats/derived/MonoidKTests.scala

@@ -0,0 +1,10 @@
+package cats.derived
+
+import alleycats._
+import cats._
+import cats.derived.all._
+import cats.derived.all.given
+
+class MonoidKTests { //
+  case class Foo[A](i: String, l: List[A]) derives MonoidK
+}

core/src/test/scala-3.0.0-RC3/cats/derived/SemigroupKTests.scala

@@ -0,0 +1,10 @@
+package cats.derived
+
+import alleycats._
+import cats._
+import cats.derived.all._
+import cats.derived.all.given
+
+class SemigroupKTests { //
+  case class Foo[A](i: String, l: List[A]) derives SemigroupK
+}