My absolute coordinate version of doFloat

xmonad.hs

import XMonad
import qualified XMonad.StackSet as W

main :: IO ()
main = xmonad defaultConfig
  { manageHook = composeAll
    [ className =? "XTerm" --> doFloatAbsRect 0 0 600 300 ]
  }

doFloatAbsRect :: Rational -> Rational -> Rational -> Rational -> ManageHook
doFloatAbsRect x y width height = do
  win <- ask -- get Window
  q <- liftX (floatLocation win) -- get (ScreenId, W.RationalRect)
  let sid = fst q :: ScreenId
      oirgRect = snd q :: W.RationalRect
      ss2ss ss = -- :: StackSet ... -> StackSet ...
        W.float win newRect ss where
          mapping = map (\s -> (W.screen s, W.screenDetail s)) (c:v) where
            c = W.current ss
            v = W.visible ss
          maybeSD = lookup sid mapping
          scRect  = fmap screenRect maybeSD
          newRect = case scRect of
            Nothing -> oirgRect
            Just (Rectangle x0 y0 w0 h0) ->
              W.RationalRect x' y' w' h' where
                W.RationalRect x1 y1 w1 h1 = oirgRect
                x' = if x0 == 0 then x1 else x / (fromIntegral x0)
                y' = if y0 == 0 then y1 else y / (fromIntegral y0)
                w' = if w0 == 0 then w1 else width / (fromIntegral w0)
                h' = if h0 == 0 then h1 else height / (fromIntegral h0)
  doF ss2ss