Monoid instance for Message

Data/OpenPGP.hs

@@ -67,6 +67,7 @@ import Numeric
 import Control.Monad
 import Control.Arrow
 import Control.Applicative
+import Data.Monoid
 import Data.Bits
 import Data.Word
 import Data.Char
@@ -883,6 +884,10 @@ instance BINARY_CLASS Message where
 	put (Message xs) = mapM_ put xs
 	get = fmap Message listUntilEnd
 
+instance Monoid Message where
+	mempty = Message []
+	mappend (Message a) (Message b) = Message (a ++ b)
+
 -- | Extract all signature and data packets from a 'Message'
 signatures_and_data :: Message -> ([Packet], [Packet])
 signatures_and_data (Message ((CompressedDataPacket {message = m}):_)) =