harbl-cli/src/Hosts.hs

   1 -- | A newtype around a list of Strings which represent hosts to look up.
   2 --   This is all to avoid an orphan instance of 'Configured' for
   3 --   [String] if we had defined one in e.g. 'OptionalConfiguration'.
   4 --
   5 {-# LANGUAGE DeriveDataTypeable #-}
   6 {-# LANGUAGE GeneralizedNewtypeDeriving #-}
   7
   8 module Hosts ( Hosts(..) )
   9 where
  10
  11 import Data.Configurator () -- Needed for predefined instances.
  12 import Data.Configurator.Types ( Configured(..) )
  13 import Data.Monoid ( Monoid )
  14 import Data.Data ( Data )
  15 import System.Console.CmdArgs.Default ( Default(..) )
  16 import Data.Typeable ( Typeable )
  17
  18 import Configurator ( convert_newtype_list )
  19
  20
  21 -- | A (wrapper around a) list of hosts.
  22 --
  23 newtype Hosts =
  24   Hosts { get_hosts :: [String] }
  25     deriving (Data, Eq, Monoid, Show, Typeable)
  26
  27
  28 -- | The default list of hosts. It's empty.
  29 --
  30 instance Default Hosts where def = Hosts []
  31
  32 instance Configured Hosts where
  33   -- | This allows us to read a Hosts object out of a Configurator
  34   --   config file: by default Configurator wouldn't know what to do.
  35   convert = convert_newtype_list Hosts