Add NoPersist and use it in Logger.hs

1 files changed, 23 insertions, 0 deletions

diff --git a/src/Internal/NoPersist.hs b/src/Internal/NoPersist.hs
new file mode 100644
index 0000000..a67e649
--- /dev/null
+++ b/src/Internal/NoPersist.hs
@@ -0,0 +1,23 @@
+-- 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