    {-# OPTIONS_GHC -fglasgow-exts #-} -- For deriving Data/Typeable
    {-# LANGUAGE FlexibleInstances, GeneralizedNewtypeDeriving, MultiParamTypeClasses #-}

    -----------------------------------------------------------------------------
    -- |
    -- Module      :  XMonad.Layout.ResizableTile
    -- Copyright   :  (c) MATSUYAMA Tomohiro <t.matsuyama.pub@gmail.com>
    -- License     :  BSD-style (see LICENSE)
    --
    -- Maintainer  :  MATSUYAMA Tomohiro <t.matsuyama.pub@gmail.com>
    -- Stability   :  unstable
    -- Portability :  unportable
    --
    -- More useful tiled layout that allows you to change a width\/height of window.
    --
    -----------------------------------------------------------------------------

    module XMonad.Layout.ResizableTile (
                                        -- * Usage
                                        -- $usage
                                        ResizableTall(..), MirrorResize(..)
                                       ) where

    import XMonad hiding (tile, splitVertically, splitHorizontallyBy)
    import qualified XMonad.StackSet as W
    import Control.Monad
    import qualified Data.Map as M
    import Data.List ((\\))

    -- $usage
    -- You can use this module with the following in your @~\/.xmonad\/xmonad.hs@:
    --
    -- > import XMonad.Layout.ResizableTile
    --
    -- Then edit your @layoutHook@ by adding the ResizableTile layout:
    --
    -- > myLayouts =  ResizableTall 1 (3/100) (1/2) [] ||| etc..
    -- > main = xmonad defaultConfig { layoutHook = myLayouts }
    --
    -- For more detailed instructions on editing the layoutHook see:
    --
    -- "XMonad.Doc.Extending#Editing_the_layout_hook"
    --
    -- You may also want to add the following key bindings:
    --
    -- > , ((modMask x,               xK_a), sendMessage MirrorShrink)
    -- > , ((modMask x,               xK_z), sendMessage MirrorExpand)
    --
    -- For detailed instruction on editing the key binding see:
    --
    -- "XMonad.Doc.Extending#Editing_key_bindings".

    data MirrorResize = MirrorShrink | MirrorExpand deriving Typeable
    instance Message MirrorResize

    data ResizableTall a = ResizableTall Int Rational Rational [Rational] deriving (Show, Read)
    instance LayoutClass ResizableTall a where
        doLayout (ResizableTall nmaster _ frac mfrac) r =
            return . (\x->(x,Nothing)) .
            ap zip (tile frac (mfrac ++ repeat 1) r nmaster . length) . W.integrate
        handleMessage (ResizableTall nmaster delta frac mfrac) m =
            do ms <- (W.stack . W.workspace . W.current) `fmap` gets windowset
               fs <- (M.keys . W.floating) `fmap` gets windowset
               return $ ms >>= unfloat fs >>= handleMesg
            where handleMesg s = msum [fmap resize (fromMessage m)
                                      ,fmap (\x -> mresize x s) (fromMessage m)
                                      ,fmap incmastern (fromMessage m)]
                  unfloat fs s = if W.focus s `elem` fs
                                   then Nothing
                                   else Just (s { W.up = (W.up s) \\ fs
                                                , W.down = (W.down s) \\ fs })
                  resize Shrink = ResizableTall nmaster delta (max 0 $ frac-delta) mfrac
                  resize Expand = ResizableTall nmaster delta (min 1 $ frac+delta) mfrac
                  mresize MirrorShrink s = mresize' s delta
                  mresize MirrorExpand s = mresize' s (0-delta)
                  mresize' s d = let n = length $ W.up s
                                     total = n + (length $ W.down s) + 1
                                     pos = if n == (nmaster-1) || n == (total-1) then n-1 else n
                                     mfrac' = modifymfrac (mfrac ++ repeat 1) d pos
                                 in ResizableTall nmaster delta frac $ take total mfrac'
                  modifymfrac [] _ _ = []
                  modifymfrac (f:fx) d n | n == 0    = f+d : fx
                                         | otherwise = f : modifymfrac fx d (n-1)
                  incmastern (IncMasterN d) = ResizableTall (max 0 (nmaster+d)) delta frac mfrac
        description _ = "ResizableTall"

    tile :: Rational -> [Rational] -> Rectangle -> Int -> Int -> [Rectangle]
    tile f mf r nmaster n = if n <= nmaster || nmaster == 0
        then splitVertically mf n r
        else splitVertically mf nmaster r1 ++ splitVertically (drop nmaster mf) (n-nmaster) r2 -- two columns
      where (r1,r2) = splitHorizontallyBy f r

    splitVertically :: RealFrac r => [r] -> Int -> Rectangle -> [Rectangle]
    splitVertically [] _ r = [r]
    splitVertically _ n r | n < 2 = [r]
    splitVertically (f:fx) n (Rectangle sx sy sw sh) = Rectangle sx sy sw smallh :
        splitVertically fx (n-1) (Rectangle sx (sy+fromIntegral smallh) sw (sh-smallh))
      where smallh = floor $ fromIntegral (sh `div` fromIntegral n) * f --hmm, this is a fold or map.

    splitHorizontallyBy :: RealFrac r => r -> Rectangle -> (Rectangle, Rectangle)
    splitHorizontallyBy f (Rectangle sx sy sw sh) =
        ( Rectangle sx sy leftw sh
        , Rectangle (sx + fromIntegral leftw) sy (sw-fromIntegral leftw) sh)
      where leftw = floor $ fromIntegral sw * f