{-# LANGUAGE DeriveDataTypeable #-} -- | A newtype around a list of Strings which represent the MXes whose -- remote forwards we don't report. This is all to avoid an orphan -- instance of Configured for [String] if we had defined one in -- e.g. 'OptionalConfiguration'. -- module MxList where -- DC is needed only for the DCT.Configured instance of String. import qualified Data.Configurator as DC() import qualified Data.Configurator.Types as DCT ( Configured, Value( List ), convert ) import Data.Data (Data) import System.Console.CmdArgs.Default (Default(..)) import Data.Typeable (Typeable) -- | A (wrapper around a) list of MX hostnames. -- newtype MxList = MxList { get_mxs :: [String] } deriving (Data, Show, Typeable) -- | The default (empty) list of MXes. -- instance Default MxList where def = MxList [] instance DCT.Configured MxList where -- | This allows us to read a MxList 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 MxList constructor to -- it. convert (DCT.List xs) = -- mapM gives us a Maybe [String] here. fmap MxList (mapM convert_string xs) where convert_string :: DCT.Value -> Maybe String convert_string = DCT.convert -- If we read anything other than a list of values out of the file, -- fail. convert _ = Nothing