mirror of
https://github.com/xmonad/xmonad-contrib.git
synced 2025-07-30 03:31:51 -07:00
94662bffc6
This change needs base-4.9.0.0 or later so that we can include Control.Monad.Fail. We could jump through hoops to support older compilers still, but it feels like it's not worthwhile.
49 lines
1.6 KiB
Haskell
49 lines
1.6 KiB
Haskell
{-# LANGUAGE GeneralizedNewtypeDeriving #-}
|
|
|
|
-----------------------------------------------------------------------------
|
|
-- |
|
|
-- Module : XMonad.Util.Invisible
|
|
-- Copyright : (c) 2007 Andrea Rossato, David Roundy
|
|
-- License : BSD-style (see xmonad/LICENSE)
|
|
--
|
|
-- Maintainer : andrea.rossato@unibz.it
|
|
-- Stability : unstable
|
|
-- Portability : unportable
|
|
--
|
|
-- A data type to store the layout state
|
|
--
|
|
-----------------------------------------------------------------------------
|
|
|
|
module XMonad.Util.Invisible (
|
|
-- * Usage:
|
|
-- $usage
|
|
Invisible (..)
|
|
, whenIJust
|
|
, fromIMaybe
|
|
) where
|
|
|
|
import Control.Applicative
|
|
import Control.Monad.Fail
|
|
|
|
-- $usage
|
|
-- A wrapper data type to store layout state that shouldn't be persisted across
|
|
-- restarts. A common wrapped type to use is @Maybe a@.
|
|
-- Invisible derives trivial definitions for Read and Show, so the wrapped data
|
|
-- type need not do so.
|
|
|
|
newtype Invisible m a = I (m a) deriving (Monad, MonadFail, Applicative, Functor)
|
|
|
|
instance (Functor m, Monad m, MonadFail m) => Read (Invisible m a) where
|
|
readsPrec _ s = [(Control.Monad.Fail.fail "Read Invisible", s)]
|
|
|
|
instance Monad m => Show (Invisible m a) where
|
|
show _ = ""
|
|
|
|
whenIJust :: (Monad m) => Invisible Maybe a -> (a -> m ()) -> m ()
|
|
whenIJust (I (Just x)) f = f x
|
|
whenIJust (I Nothing) _ = return ()
|
|
|
|
fromIMaybe :: a -> Invisible Maybe a -> a
|
|
fromIMaybe _ (I (Just x)) = x
|
|
fromIMaybe a (I Nothing) = a
|