    --------------------------------------------------------------------
    -- |
    -- Module     : XMonad.Util.CustomKeys
    -- Copyright  : (c) 2007 Valery V. Vorotyntsev
    -- License    : BSD3-style (see LICENSE)
    --
    -- Maintainer : Valery V. Vorotynsev <valery.vv@gmail.com>
    --
    -- Customized key bindings.
    --
    -- (See also "XMonad.Util.EZConfig" in xmonad-contrib.)
    --------------------------------------------------------------------

    module XMonad.Util.CustomKeys (
                                  -- * Usage
                                  -- $usage
                                   customKeys
                                  , customKeysFrom
                                  ) where

    import XMonad
    import Control.Monad.Reader

    import qualified Data.Map as M

    -- $usage
    --
    -- 1. In @~\/.xmonad\/xmonad.hs@ add:
    --
    -- > import XMonad.Util.CustomKeys
    --
    -- 2. Set key bindings with 'customKeys':
    --
    -- > main = xmonad defaultConfig { keys = customKeys delkeys inskeys }
    -- >     where
    -- >       delkeys :: XConfig l -> [(KeyMask, KeySym)]
    -- >       delkeys XConfig {modMask = modm} =
    -- >           -- we're preferring Futurama to Xinerama here
    -- >           [ (modm .|. m, k) | (m, k) <- zip [0, shiftMask] [xK_w, xK_e, xK_r] ]
    -- >
    -- >       inskeys :: XConfig l -> [((KeyMask, KeySym), X ())]
    -- >       inskeys conf@(XConfig {modMask = modm}) =
    -- >           [ ((mod1Mask,             xK_F2  ), spawn $ terminal conf)
    -- >           , ((modm .|. controlMask, xK_F11 ), spawn "xscreensaver-command -lock")
    -- >           , ((mod1Mask,             xK_Down), spawn "amixer set Master 1-")
    -- >           , ((mod1Mask,             xK_Up  ), spawn "amixer set Master 1+")
    -- >           ]
    --
    -- 0 (/hidden feature/). You can always replace bindings map
    --   entirely. No need to import "CustomKeys" this time:
    --
    -- > import XMonad
    -- > import System.Exit
    -- > import qualified Data.Map as M
    -- >
    -- > main = xmonad defaultConfig {
    -- >          keys = \_ -> M.fromList [
    -- >                  -- Let me out of here! I want my KDE back! Help! Help!
    -- >                  ( (0, xK_Escape), io (exitWith ExitSuccess) ) ] }

    -- | Customize 'XMonad.Config.defaultConfig' -- delete needless
    -- shortcuts and insert those you will use.
    customKeys :: (XConfig Layout -> [(KeyMask, KeySym)]) -- ^ shortcuts to delete
               -> (XConfig Layout -> [((KeyMask, KeySym), X ())]) -- ^ key bindings to insert
               -> XConfig Layout -> M.Map (KeyMask, KeySym) (X ())
    customKeys = customKeysFrom defaultConfig

    -- | General variant of 'customKeys': customize key bindings of
    -- third-party configuration.
    customKeysFrom :: XConfig l -- ^ original configuration
                   -> (XConfig Layout -> [(KeyMask, KeySym)]) -- ^ shortcuts to delete
                   -> (XConfig Layout -> [((KeyMask, KeySym), X ())]) -- ^ key bindings to insert
                   -> XConfig Layout -> M.Map (KeyMask, KeySym) (X ())
    customKeysFrom conf = (runReader .) . customize conf

    customize :: XConfig l
              -> (XConfig Layout -> [(KeyMask, KeySym)])
              -> (XConfig Layout -> [((KeyMask, KeySym), X ())])
              -> Reader (XConfig Layout) (M.Map (KeyMask, KeySym) (X ()))
    customize conf ds is = Reader (keys conf) >>= delete ds >>= insert is

    delete :: (MonadReader r m, Ord a) => (r -> [a]) -> M.Map a b -> m (M.Map a b)
    delete dels kmap = asks dels >>= return . foldr M.delete kmap

    insert :: (MonadReader r m, Ord a) =>
              (r -> [(a, b)]) -> M.Map a b -> m (M.Map a b)
    insert ins kmap = asks ins >>= return . foldr (uncurry M.insert) kmap