From 9400e3a3ee6f3b33a5eefe2f563ba92e9a8e24a4 Mon Sep 17 00:00:00 2001
From: Rob Rix <rob.rix@github.com>
Date: Mon, 14 Mar 2016 22:51:54 -0400
Subject: [PATCH] `coalesce` operates within an Alternative functor.

---
 test/Data/Adjoined/Spec.hs | 9 +++++----
 1 file changed, 5 insertions(+), 4 deletions(-)

diff --git a/test/Data/Adjoined/Spec.hs b/test/Data/Adjoined/Spec.hs
index bd2a1da23..3ce8b726a 100644
--- a/test/Data/Adjoined/Spec.hs
+++ b/test/Data/Adjoined/Spec.hs
@@ -1,5 +1,6 @@
 module Data.Adjoined.Spec (spec) where
 
+import Control.Applicative
 import Data.Adjoined
 import Data.Coalescent
 import Data.Typeable
@@ -43,7 +44,7 @@ instance Arbitrary a => Arbitrary (Uncoalesced a) where
   arbitrary = Uncoalesced <$> arbitrary
 
 instance Coalescent (Uncoalesced a) where
-  coalesce _ _ = Nothing
+  coalesce a b = pure a <|> pure b
 
 
 -- | A wrapper which always coalesces values.
@@ -54,7 +55,7 @@ instance Arbitrary a => Arbitrary (Coalesced a) where
   arbitrary = Coalesced <$> arbitrary
 
 instance Monoid a => Coalescent (Coalesced a) where
-  coalesce a b = Just (Coalesced (runCoalesced a `mappend` runCoalesced b))
+  coalesce a b = pure (Coalesced (runCoalesced a `mappend` runCoalesced b))
 
 
 -- | A wrapper which coalesces asymmetrically.
@@ -67,8 +68,8 @@ instance Arbitrary a => Arbitrary (Semicoalesced a) where
   arbitrary = Semicoalesced <$> arbitrary
 
 instance Monoid a => Coalescent (Semicoalesced a) where
-  Semicoalesced (True, a) `coalesce` Semicoalesced (flag, b) = Just (Semicoalesced (flag, a `mappend` b))
-  Semicoalesced (False, _) `coalesce` _ = Nothing
+  Semicoalesced (True, a) `coalesce` Semicoalesced (flag, b) = pure (Semicoalesced (flag, a `mappend` b))
+  a `coalesce` b = pure a <|> pure b
 
 
 -- | Returns a string with the name of a type.