src/Usernames.hs

   1 {-# LANGUAGE DeriveDataTypeable #-}
   2
   3 -- | A newtype around a list of Strings which represent the usernames
   4 --   to watch. This is all to avoid an orphan instance of Configured
   5 --   for [String] if we had defined one in e.g. OptionalConfiguration.
   6 --
   7 module Usernames ( Usernames(..) )
   8 where
   9
  10 -- DC is needed only for the DCT.Configured instance of String.
  11 import qualified Data.Configurator as DC()
  12 import qualified Data.Configurator.Types as DCT
  13 import Data.Data ( Data )
  14 import System.Console.CmdArgs.Default ( Default(..) )
  15 import Data.Typeable ( Typeable )
  16
  17
  18 newtype Usernames =
  19   Usernames { get_usernames :: [String] }
  20     deriving (Data, Show, Typeable)
  21
  22
  23 instance Default Usernames where
  24   def = Usernames []
  25
  26
  27 instance DCT.Configured Usernames where
  28   convert (DCT.List xs) =
  29     fmap Usernames (mapM convert_string xs)
  30     where
  31       convert_string :: DCT.Value -> Maybe String
  32       convert_string = DCT.convert
  33
  34   convert _ = Nothing