Extensions: Monoid instance for Extensions.

[API change]

1 files changed, 5 insertions, 1 deletions

diff --git a/src/Text/Pandoc/Extensions.hs b/src/Text/Pandoc/Extensions.hs
index 398944d47..79e3529e9 100644
--- a/src/Text/Pandoc/Extensions.hs
+++ b/src/Text/Pandoc/Extensions.hs
@@ -45,7 +45,7 @@ module Text.Pandoc.Extensions ( Extension(..)
                               , githubMarkdownExtensions
                               , multimarkdownExtensions )
 where
-import Data.Bits (clearBit, setBit, testBit)
+import Data.Bits (clearBit, setBit, testBit, (.|.))
 import Data.Data (Data)
 import Data.Typeable (Typeable)
 import GHC.Generics (Generic)
@@ -55,6 +55,10 @@ import Text.Parsec
 newtype Extensions = Extensions Integer
   deriving (Show, Read, Eq, Ord, Data, Typeable, Generic)
 
+instance Monoid Extensions where
+  mempty = Extensions 0
+  mappend (Extensions a) (Extensions b) = Extensions (a .|. b)
+
 extensionsFromList :: [Extension] -> Extensions
 extensionsFromList = foldr enableExtension emptyExtensions