From d2ee5b2b0eb2afb970ab8d4feed84434dc8236e0 Mon Sep 17 00:00:00 2001
From: Veronika Romashkina <vrom911@gmail.com>
Date: Wed, 26 Feb 2020 10:49:03 +0000
Subject: Support GHC-8.8

Add MonadFail instances and constraints.
---
 lib/Hakyll/Core/Compiler/Internal.hs | 8 +++++++-
 lib/Hakyll/Core/Metadata.hs          | 2 +-
 lib/Hakyll/Core/Rules/Internal.hs    | 2 +-
 3 files changed, 9 insertions(+), 3 deletions(-)

(limited to 'lib/Hakyll/Core')

diff --git a/lib/Hakyll/Core/Compiler/Internal.hs b/lib/Hakyll/Core/Compiler/Internal.hs
index 762630c..3b62e2d 100644
--- a/lib/Hakyll/Core/Compiler/Internal.hs
+++ b/lib/Hakyll/Core/Compiler/Internal.hs
@@ -40,6 +40,7 @@ module Hakyll.Core.Compiler.Internal
 import           Control.Applicative            (Alternative (..))
 import           Control.Exception              (SomeException, handle)
 import           Control.Monad                  (forM_)
+import qualified Control.Monad.Fail             as Fail
 import           Control.Monad.Except           (MonadError (..))
 import           Data.List.NonEmpty             (NonEmpty (..))
 import qualified Data.List.NonEmpty             as NonEmpty
@@ -183,9 +184,14 @@ instance Monad Compiler where
             CompilerError e       -> return $ CompilerError e
     {-# INLINE (>>=) #-}
 
-    fail = compilerThrow . return
+#if !(MIN_VERSION_base(4,13,0))
+    fail = Fail.fail
     {-# INLINE fail #-}
+#endif
 
+instance Fail.MonadFail Compiler where
+    fail = compilerThrow . return
+    {-# INLINE fail #-}
 
 --------------------------------------------------------------------------------
 instance Applicative Compiler where
diff --git a/lib/Hakyll/Core/Metadata.hs b/lib/Hakyll/Core/Metadata.hs
index 1cf536e..9d99857 100644
--- a/lib/Hakyll/Core/Metadata.hs
+++ b/lib/Hakyll/Core/Metadata.hs
@@ -66,7 +66,7 @@ getMetadataField identifier key = do
 --------------------------------------------------------------------------------
 -- | Version of 'getMetadataField' which throws an error if the field does not
 -- exist.
-getMetadataField' :: MonadMetadata m => Identifier -> String -> m String
+getMetadataField' :: (MonadFail m, MonadMetadata m) => Identifier -> String -> m String
 getMetadataField' identifier key = do
     field <- getMetadataField identifier key
     case field of
diff --git a/lib/Hakyll/Core/Rules/Internal.hs b/lib/Hakyll/Core/Rules/Internal.hs
index 647af74..2617798 100644
--- a/lib/Hakyll/Core/Rules/Internal.hs
+++ b/lib/Hakyll/Core/Rules/Internal.hs
@@ -88,7 +88,7 @@ emptyRulesState = RulesState Nothing Nothing
 -- | The monad used to compose rules
 newtype Rules a = Rules
     { unRules :: RWST RulesRead RuleSet RulesState IO a
-    } deriving (Monad, Functor, Applicative)
+    } deriving (Monad, MonadFail, Functor, Applicative)
 
 
 --------------------------------------------------------------------------------
-- 
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