Support GHC-8.8

Add MonadFail instances and constraints.

5 files changed, 14 insertions, 8 deletions

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)
 
 
 --------------------------------------------------------------------------------
diff --git a/lib/Hakyll/Web/Template/Context.hs b/lib/Hakyll/Web/Template/Context.hs
index 8627d5b..a5049c2 100644
--- a/lib/Hakyll/Web/Template/Context.hs
+++ b/lib/Hakyll/Web/Template/Context.hs
@@ -365,7 +365,7 @@ dateFieldWith locale key format = field key $ \i -> do
 -- | Parser to try to extract and parse the time from the @published@
 -- field or from the filename. See 'dateField' for more information.
 -- Exported for user convenience.
-getItemUTC :: MonadMetadata m
+getItemUTC :: (MonadMetadata m, MonadFail m)
            => TimeLocale        -- ^ Output time locale
            -> Identifier        -- ^ Input page
            -> m UTCTime         -- ^ Parsed UTCTime
diff --git a/lib/Hakyll/Web/Template/List.hs b/lib/Hakyll/Web/Template/List.hs
index 4d769fc..db3fff1 100644
--- a/lib/Hakyll/Web/Template/List.hs
+++ b/lib/Hakyll/Web/Template/List.hs
@@ -60,7 +60,7 @@ applyJoinTemplateList delimiter tpl context items = do
 --------------------------------------------------------------------------------
 -- | Sort pages chronologically. Uses the same method as 'dateField' for
 -- extracting the date.
-chronological :: MonadMetadata m => [Item a] -> m [Item a]
+chronological :: (MonadMetadata m, MonadFail m) => [Item a] -> m [Item a]
 chronological =
     sortByM $ getItemUTC defaultTimeLocale . itemIdentifier
   where
@@ -71,14 +71,14 @@ chronological =
 
 --------------------------------------------------------------------------------
 -- | The reverse of 'chronological'
-recentFirst :: MonadMetadata m => [Item a] -> m [Item a]
+recentFirst :: (MonadMetadata m, MonadFail m) => [Item a] -> m [Item a]
 recentFirst = liftM reverse . chronological
 
 
 --------------------------------------------------------------------------------
 -- | Version of 'chronological' which doesn't need the actual items.
 sortChronological
-    :: MonadMetadata m => [Identifier] -> m [Identifier]
+    :: (MonadMetadata m, MonadFail m) => [Identifier] -> m [Identifier]
 sortChronological ids =
     liftM (map itemIdentifier) $ chronological [Item i () | i <- ids]
 
@@ -86,6 +86,6 @@ sortChronological ids =
 --------------------------------------------------------------------------------
 -- | Version of 'recentFirst' which doesn't need the actual items.
 sortRecentFirst
-    :: MonadMetadata m => [Identifier] -> m [Identifier]
+    :: (MonadMetadata m, MonadFail m) => [Identifier] -> m [Identifier]
 sortRecentFirst ids =
     liftM (map itemIdentifier) $ recentFirst [Item i () | i <- ids]