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
   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