From 2e0ba8479fb0554596954e2089a39a1219dbe77d Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Baldur=20Bl=C3=B6ndal?= <baldur.blondal@iohk.io>
Date: Wed, 21 Feb 2024 14:25:10 +0000
Subject: [PATCH] Applicative, Alternative instances for Cayley.

---
 CHANGELOG.markdown            |  1 +
 src/Data/Profunctor/Cayley.hs | 17 ++++++++++++++---
 2 files changed, 15 insertions(+), 3 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..c3603930 100644
--- a/src/Data/Profunctor/Cayley.hs
+++ b/src/Data/Profunctor/Cayley.hs
@@ -1,7 +1,12 @@
-{-# LANGUAGE DeriveTraversable #-}
-{-# LANGUAGE DeriveGeneric #-}
+{-# LANGUAGE CPP #-}
+Hello: __GLASGOW_HASKELL__
 {-# LANGUAGE DeriveDataTypeable #-}
+{-# LANGUAGE DeriveGeneric #-}
+{-# LANGUAGE DeriveTraversable #-}
+#if __GLASGOW_HASKELL__ < 811
 {-# LANGUAGE DerivingStrategies #-}
+#endif
+{-# LANGUAGE DerivingVia #-}
 {-# LANGUAGE PolyKinds #-}
 {-# LANGUAGE RankNTypes #-}
 {-# LANGUAGE StandaloneDeriving #-}
@@ -21,11 +26,13 @@ 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
@@ -45,6 +52,10 @@ newtype Cayley f p a b = Cayley { runCayley :: f (p a b) }
 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