Added Invisible to store layout state

Invisible is a data type to store information that will be lost when
restarting XMonad (the idea came from David Roundy)

darcs-hash:20070928190107-32816-ce095723ac5deb5cde50eab871416e3edee1e875.gz

1 files changed, 42 insertions, 0 deletions

diff --git a/Invisible.hs b/Invisible.hs
new file mode 100644
index 0000000..5d040f7
--- /dev/null
+++ b/Invisible.hs
@@ -0,0 +1,42 @@
+-----------------------------------------------------------------------------
+-- |
+-- Module      :  XMonadContrib.Invisible
+-- Copyright   :  (c) 2007 Andrea Rossato, David Roundy
+-- License     :  BSD-style (see xmonad/LICENSE)
+-- 
+-- Maintainer  :  andrea.rossato@unibz.it, droundy@darcs.net
+-- Stability   :  unstable
+-- Portability :  unportable
+--
+-- A data type to store the layout state
+--
+-----------------------------------------------------------------------------
+
+module XMonadContrib.Invisible ( 
+                             -- * Usage:
+                             -- $usage
+                             Invisible (..)
+                            , whenIJust
+                            ) where
+
+-- $usage
+-- A data type to store the layout state
+
+data Invisible m a = I (m a)
+
+instance (Functor m, Monad m) => Read (Invisible m a) where
+    readsPrec _ s = [(fail "Read Invisible", s)]
+
+instance Monad m => Show (Invisible m a) where
+    show _ = ""
+
+instance (Functor m, Monad m) => Monad (Invisible m) where
+    return a = I (return a)
+    m >>= f  = m >>= f
+
+instance (Functor m, Monad m) => Functor (Invisible m) where
+    fmap f (I x) = I (fmap f x)
+
+whenIJust :: (Monad m) => Invisible Maybe a -> (a -> m ()) -> m ()
+whenIJust (I (Just x)) f  = f x
+whenIJust (I  Nothing) _  = return ()