-- Module for not persisting XMonad state. To be used with ExtensibleState
-- for data types that cannot be persisted.
module Internal.NoPersist where

import Data.Default (Default, def)
import Data.Typeable

import XMonad (ExtensionClass(..))

newtype NoPersist a = NoPersist a
  deriving (Typeable)

instance Show (NoPersist a) where
  show (NoPersist _) = show ()

instance (Default a) => Read (NoPersist a) where
  readsPrec i s = map (\(_, s) -> (NoPersist def, s)) (readsPrec i s :: [((), String)])

instance (Default a) => Default (NoPersist a) where
  def = NoPersist def

instance (Default a, Typeable a) => ExtensionClass (NoPersist a) where
  initialValue = NoPersist def