From a08f6e400772899b9b0fc16befc50391cd70696b Mon Sep 17 00:00:00 2001
From: Felix Yan <felixonmars@archlinux.org>
Date: Fri, 18 May 2018 16:24:41 +0800
Subject: [PATCH] GHC 8.4 support

---
 src/Term/Maude/Signature.hs          |  8 ++--
 src/Term/Rewriting/Definitions.hs    | 23 ++++++----
 src/Term/Unification.hs              |  4 +-
 11 files changed, 79 insertions(+), 48 deletions(-)

diff --git a/src/Term/Maude/Signature.hs b/src/Term/Maude/Signature.hs
index 98c25d9f..1a4ce82f 100644
--- a/src/Term/Maude/Signature.hs
+++ b/src/Term/Maude/Signature.hs
@@ -104,9 +104,9 @@ maudeSig msig@(MaudeSig {enableDH,enableBP,enableMSet,enableXor,enableDiff=_,stF
           `S.union` dhReducibleFunSig `S.union` bpReducibleFunSig `S.union` xorReducibleFunSig
 
 -- | A monoid instance to combine maude signatures.
-instance Monoid MaudeSig where
-    (MaudeSig dh1 bp1 mset1 xor1 diff1 stFunSyms1 stRules1 _ _) `mappend`
-      (MaudeSig dh2 bp2 mset2 xor2 diff2 stFunSyms2 stRules2 _ _) =
+instance Semigroup MaudeSig where
+    MaudeSig dh1 bp1 mset1 xor1 diff1 stFunSyms1 stRules1 _ _ <>
+      MaudeSig dh2 bp2 mset2 xor2 diff2 stFunSyms2 stRules2 _ _ =
           maudeSig (mempty {enableDH=dh1||dh2
                            ,enableBP=bp1||bp2
                            ,enableMSet=mset1||mset2
@@ -114,6 +114,8 @@ instance Monoid MaudeSig where
                            ,enableDiff=diff1||diff2
                            ,stFunSyms=S.union stFunSyms1 stFunSyms2
                            ,stRules=S.union stRules1 stRules2})
+
+instance Monoid MaudeSig where
     mempty = MaudeSig False False False False False S.empty S.empty S.empty S.empty
 
 -- | Non-AC function symbols.
diff --git a/src/Term/Rewriting/Definitions.hs b/src/Term/Rewriting/Definitions.hs
index bd942b6a..18562e4e 100644
--- a/src/Term/Rewriting/Definitions.hs
+++ b/src/Term/Rewriting/Definitions.hs
@@ -44,10 +44,12 @@ evalEqual (Equal l r) = l == r
 instance Functor Equal where
     fmap f (Equal lhs rhs) = Equal (f lhs) (f rhs)
 
+instance Semigroup a => Semigroup (Equal a) where
+    (Equal l1 r1) <> (Equal l2 r2) =
+        Equal (l1 <> l2) (r1 <> r2)
+
 instance Monoid a => Monoid (Equal a) where
     mempty                                = Equal mempty mempty
-    (Equal l1 r1) `mappend` (Equal l2 r2) =
-        Equal (l1 `mappend` l2) (r1 `mappend` r2)
 
 instance Foldable Equal where
     foldMap f (Equal l r) = f l `mappend` f r
@@ -104,14 +106,15 @@ instance Functor Match where
     fmap _ NoMatch             = NoMatch
     fmap f (DelayedMatches ms) = DelayedMatches (fmap (f *** f) ms)
 
+instance Semigroup (Match a) where
+    NoMatch            <> _                  = NoMatch
+    _                  <> NoMatch            = NoMatch
+    DelayedMatches ms1 <> DelayedMatches ms2 =
+        DelayedMatches (ms1 <> ms2)
+
 instance Monoid (Match a) where
     mempty = DelayedMatches []
 
-    NoMatch            `mappend` _                  = NoMatch
-    _                  `mappend` NoMatch            = NoMatch
-    DelayedMatches ms1 `mappend` DelayedMatches ms2 =
-        DelayedMatches (ms1 `mappend` ms2)
-
 
 instance Foldable Match where
     foldMap _ NoMatch             = mempty
@@ -136,10 +139,12 @@ data RRule a = RRule a a
 instance Functor RRule where
     fmap f (RRule lhs rhs) = RRule (f lhs) (f rhs)
 
+instance Monoid a => Semigroup (RRule a) where
+    (RRule l1 r1) <> (RRule l2 r2) =
+        RRule (l1 <> l2) (r1 <> r2)
+
 instance Monoid a => Monoid (RRule a) where
     mempty                                = RRule mempty mempty
-    (RRule l1 r1) `mappend` (RRule l2 r2) =
-        RRule (l1 `mappend` l2) (r1 `mappend` r2)
 
 instance Foldable RRule where
     foldMap f (RRule l r) = f l `mappend` f r
diff --git a/src/Term/Unification.hs b/src/Term/Unification.hs
index e1de0163..7ce6bb41 100644
--- a/src/Term/Unification.hs
+++ b/src/Term/Unification.hs
@@ -265,9 +265,11 @@ unifyRaw l0 r0 = do
 
 data MatchFailure = NoMatcher | ACProblem
 
+instance Semigroup MatchFailure where
+  _ <> _ = NoMatcher
+
 instance Monoid MatchFailure where
   mempty = NoMatcher
-  mappend _ _ = NoMatcher
 
 -- | Ensure that the computed substitution @sigma@ satisfies
 -- @t ==_AC apply sigma p@ after the delayed equations are solved.