X-Git-Url: http://gitweb.michael.orlitzky.com/?p=dead%2Fhalcyon.git;a=blobdiff_plain;f=src%2FUsernames.hs;h=e31b118405c908c1eab3e09b6fc54b43d3e18cae;hp=92e5c4376f77fc2416044941ee3457f0597727cc;hb=15fd6f764f88f79424d7caaba564e57df564b532;hpb=d7c6b5499c0969b6e488d9fc583f93bbb4e3d4c7

diff --git a/src/Usernames.hs b/src/Usernames.hs
index 92e5c43..e31b118 100644
--- a/src/Usernames.hs
+++ b/src/Usernames.hs
@@ -11,20 +11,45 @@ where
 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).
+--
 newtype Usernames =
   Usernames { get_usernames :: [String] }
     deriving (Data, Show, Typeable)
 
 
 instance Default Usernames where
+  -- | The default list of usernames is empty.
+  --
   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
+  --   Configurator config file. By default Configurator wouldn't know
+  --   what to do, so we have to tell it that we expect a list, and if
+  --   that list has strings in it, we can apply the Usernames
+  --   constructor to it.
   convert (DCT.List xs) =
     fmap Usernames (mapM convert_string xs)
     where