From 6fb192d0a38672c3d9e8d6671625ba9d443c69a3 Mon Sep 17 00:00:00 2001
From: Icelandjack <501899+Icelandjack@users.noreply.github.com>
Date: Wed, 21 Feb 2024 17:00:38 +0000
Subject: [PATCH] Applicative, Alternative instances for Cayley. (#109)

---
 CHANGELOG.markdown            |  1 +
 src/Data/Profunctor/Cayley.hs | 15 +++++++++++----
 2 files changed, 12 insertions(+), 4 deletions(-)

diff --git a/CHANGELOG.markdown b/CHANGELOG.markdown
index b26950a3..e4e4f6f6 100644
--- a/CHANGELOG.markdown
+++ b/CHANGELOG.markdown
@@ -1,5 +1,6 @@
 6 [unreleased]
 --------------
+* `Applicative`, `Alternative` instances for `Cayley`
 * Removed support for GHC < 8.6
 * Inverted dependency between `distributive` v1 and `profunctors` v6
 * `Data.Profunctor.Mapping`, `Data.Profunctor.Closed`, `Data.Profunctor.Rep`
diff --git a/src/Data/Profunctor/Cayley.hs b/src/Data/Profunctor/Cayley.hs
index 6b37d62f..5664b275 100644
--- a/src/Data/Profunctor/Cayley.hs
+++ b/src/Data/Profunctor/Cayley.hs
@@ -1,7 +1,7 @@
-{-# LANGUAGE DeriveTraversable #-}
-{-# LANGUAGE DeriveGeneric #-}
 {-# LANGUAGE DeriveDataTypeable #-}
-{-# LANGUAGE DerivingStrategies #-}
+{-# LANGUAGE DeriveGeneric #-}
+{-# LANGUAGE DeriveTraversable #-}
+{-# LANGUAGE DerivingVia #-}
 {-# LANGUAGE PolyKinds #-}
 {-# LANGUAGE RankNTypes #-}
 {-# LANGUAGE StandaloneDeriving #-}
@@ -21,11 +21,13 @@ import Control.Arrow as A
 import Control.Category
 import Control.Comonad
 import Data.Biapplicative
+import Data.Bifoldable
 import Data.Bifunctor as B
 import Data.Bifunctor.Functor
-import Data.Bifoldable
 import Data.Bitraversable
 import Data.Data
+import Data.Functor.Compose
+import Data.Kind
 import Data.Profunctor
 import Data.Profunctor.Functor
 import Data.Profunctor.Monad
@@ -46,6 +48,11 @@ deriving stock instance (Functor f, Functor (p a)) => Functor (Cayley f p a)
 deriving stock instance (Foldable f, Foldable (p a)) => Foldable (Cayley f p a)
 deriving stock instance (Traversable f, Traversable (p a)) => Traversable (Cayley f p a)
 
+deriving via Compose f (p a :: Type -> Type)
+  instance (Applicative f, Applicative (p a)) => Applicative (Cayley f p a)
+deriving via Compose f (p a :: Type -> Type)
+  instance (Alternative f, Applicative (p a)) => Alternative (Cayley f p a)
+
 instance Functor f => ProfunctorFunctor (Cayley f) where
   promap = \f -> Cayley #. fmap f .# runCayley
   {-# inline promap #-}