Merge pull request #4434 from armanbilge/topic/functor-compose-bifunctor

Add `Functor#composeBifunctor`
typelevel · May 7, 2023 · d5f7d63 · d5f7d63
2 parents d7b2288 + 3b50e1e
commit d5f7d63
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Showing 4 changed files with 15 additions and 5 deletions.
diff --git a/core/src/main/scala/cats/Bifunctor.scala b/core/src/main/scala/cats/Bifunctor.scala
@@ -138,11 +138,6 @@ object Bifunctor extends cats.instances.NTupleBifunctorInstances {
   @deprecated("Use cats.syntax object imports", "2.2.0")
   object nonInheritedOps extends ToBifunctorOps
 
-  implicit def bifunctorInFunctorInstance[F[_]: Functor, G[_, _]: Bifunctor]: Bifunctor[λ[(A, B) => F[G[A, B]]]] =
-    new Bifunctor[λ[(A, B) => F[G[A, B]]]] {
-      override def bimap[W, X, Y, Z](fab: F[G[W, X]])(f: W => Y, g: X => Z): F[G[Y, Z]] =
-        Functor[F].map(fab)(Bifunctor[G].bimap(_)(f, g))
-    }
 }
 
 private[cats] trait ComposedBifunctor[F[_, _], G[_, _]] extends Bifunctor[λ[(A, B) => F[G[A, B], G[A, B]]]] {

diff --git a/core/src/main/scala/cats/Composed.scala b/core/src/main/scala/cats/Composed.scala
@@ -46,6 +46,14 @@ private[cats] trait ComposedFunctor[F[_], G[_]] extends Functor[λ[α => F[G[α]
     F.map(fga)(ga => G.map(ga)(f))
 }
 
+private[cats] trait ComposedFunctorBifunctor[F[_], G[_, _]] extends Bifunctor[λ[(α, β) => F[G[α, β]]]] { outer =>
+  def F: Functor[F]
+  def G: Bifunctor[G]
+
+  def bimap[W, X, Y, Z](fab: F[G[W, X]])(f: W => Y, g: X => Z): F[G[Y, Z]] =
+    F.map(fab)(G.bimap(_)(f, g))
+}
+
 private[cats] trait ComposedApply[F[_], G[_]] extends Apply[λ[α => F[G[α]]]] with ComposedFunctor[F, G] { outer =>
   def F: Apply[F]
   def G: Apply[G]

diff --git a/core/src/main/scala/cats/Functor.scala b/core/src/main/scala/cats/Functor.scala
@@ -214,6 +214,12 @@ trait Functor[F[_]] extends Invariant[F] { self =>
       val G = Functor[G]
     }
 
+  def composeBifunctor[G[_, _]: Bifunctor]: Bifunctor[λ[(α, β) => F[G[α, β]]]] =
+    new ComposedFunctorBifunctor[F, G] {
+      val F = self
+      val G = Bifunctor[G]
+    }
+
   override def composeContravariant[G[_]: Contravariant]: Contravariant[λ[α => F[G[α]]]] =
     new ComposedCovariantContravariant[F, G] {
       val F = self

diff --git a/tests/shared/src/test/scala/cats/tests/BifunctorSuite.scala b/tests/shared/src/test/scala/cats/tests/BifunctorSuite.scala
@@ -48,6 +48,7 @@ class BifunctorSuite extends CatsSuite {
 
   {
     type Tuple2InsideOption[A, B] = Option[(A, B)]
+    implicit val composedBifunctor: Bifunctor[Tuple2InsideOption] = Functor[Option].composeBifunctor[(*, *)]
     checkAll(
       "Bifunctor[Option[(A, B)]",
       BifunctorTests[Tuple2InsideOption].bifunctor[String, String, String, Int, Int, Int]