import qualified Data.Configurator as DC()
import qualified Data.Configurator.Types as DCT
import Data.Data ( Data )
-import System.Console.CmdArgs.Default ( Default(..) )
+import Data.Monoid ( Monoid(..) )
import Data.Typeable ( Typeable )
+import System.Console.CmdArgs.Default ( Default(..) )
-- | Wrapper around a list of strings (usernames).
def = Usernames []
+-- | The 'Monoid' instance for 'Usernames' uses an
+-- 'Monoid' instance for lists.
+--
+instance Monoid Usernames where
+ -- | The \"empty\" 'Usernames' simply wraps an empty list.
+ mempty = Usernames []
+
+ -- | This mappend is a little funny; it always chooses the second
+ -- list if that list is nonempty. Otherwise, it chooses the
+ -- first. This is actually associative!
+ u1 `mappend` u2
+ | null (get_usernames u2) = u1
+ | otherwise = u2
+
instance DCT.Configured Usernames where
-- | This allows us to read a 'Usernames' object out of a