From 2195a82f70bec8b0fc750930645694ba7e4790ce Mon Sep 17 00:00:00 2001
From: Oleg Grenrus <oleg.grenrus@iki.fi>
Date: Sun, 7 Jan 2018 22:36:20 +0200
Subject: [PATCH] Add Semigroup (Predicate a) instance

---
 .gitignore                        | 2 ++
 src/Data/Functor/Contravariant.hs | 9 +++++++++
 2 files changed, 11 insertions(+)

diff --git a/.gitignore b/.gitignore
index 7001208..276e37b 100644
--- a/.gitignore
+++ b/.gitignore
@@ -1,2 +1,4 @@
 _darcs
 dist
+dist-newstyle
+.ghc.environment.*
diff --git a/src/Data/Functor/Contravariant.hs b/src/Data/Functor/Contravariant.hs
index 59f9986..8096afd 100644
--- a/src/Data/Functor/Contravariant.hs
+++ b/src/Data/Functor/Contravariant.hs
@@ -310,9 +310,18 @@ newtype Predicate a = Predicate { getPredicate :: a -> Bool }
 instance Contravariant Predicate where
   contramap f g = Predicate $ getPredicate g . f
 
+#if defined(MIN_VERSION_semigroups) || __GLASGOW_HASKELL__ >= 711
+instance Semigroup (Predicate a) where
+  Predicate p <> Predicate q = Predicate $ \a -> p a && q a
+#endif
+
 instance Monoid (Predicate a) where
   mempty = Predicate $ const True
+#if defined(MIN_VERSION_semigroups) || __GLASGOW_HASKELL__ >= 711
+  mappend = (<>)
+#else
   mappend (Predicate p) (Predicate q) = Predicate $ \a -> p a && q a
+#endif
 
 -- | Defines a total ordering on a type as per 'compare'
 --