Compat stuff for Monoid / Semigroup

src/PDF/Output.hs

@@ -1,3 +1,4 @@
+{-# LANGUAGE CPP #-}
 module PDF.Output (
       OBuilder(..)
     , Output(..)
@@ -13,6 +14,9 @@ module PDF.Output (
 
 import Data.ByteString.Builder (Builder, char8, lazyByteString, string8, toLazyByteString)
 import Data.ByteString.Lazy.Char8 (ByteString)
+-- #if MIN_VERSION_base(4,9,0)
+-- import qualified Data.Semigroup as Sem
+-- #endif
 import Data.String (IsString(..))
 import Control.Monad.Reader (MonadReader(..), Reader, runReader)
 import qualified PDF.EOL as EOL (Style(..))
@@ -22,9 +26,19 @@ newtype OBuilder = OBuilder (Reader EOL.Style Builder)
 lift :: (a -> Builder) -> a -> OBuilder
 lift f a = OBuilder $ return (f a)
 
+append :: OBuilder -> OBuilder -> OBuilder
+append (OBuilder a) (OBuilder b) = OBuilder (mappend <$> a <*> b)
+
+#if MIN_VERSION_base(4,9,0)
+instance Semigroup OBuilder where
+  (<>) = append
+#endif
+
 instance Monoid OBuilder where
   mempty = OBuilder (return mempty)
-  mappend (OBuilder a) (OBuilder b) = OBuilder (mappend <$> a <*> b)
+#if !(MIN_VERSION_base(4,9,0))
+  mappend = append
+#endif
 
 instance IsString OBuilder where
   fromString = string