Делаю GUI на Haskell

mkExampleWidgetHelloWorld :: WidgetInit SimpleWidget
mkExampleWidgetHelloWorld = mkSimpleWidget (WidgetMarginXY 20 10) $ defNoChildrenFns{
        onCreate = (\widget -> notifyParentOnSizeChangedAndMarkForRedraw widget $ V2 0 80)
        ,onDraw=drawFn}
    where drawFn widget canvas = do
                canvasRect <- getCanvasRect widget
                setColor canvas $ V4 0 0 255 0
                fillRect canvas canvasRect
                setColor canvas $ V4 255 0 0 0
                drawRect canvas $ shrinkRect' 5 canvasRect
                fnt <- getFont canvas ""
                drawStrAligned canvas fnt AlignCenter DrawStrFine (V4 255 255 255 0) canvasRect 
                                             "Привет, мир!"
 
mkExampleWidgetPicture :: WidgetInit SimpleWidget
mkExampleWidgetPicture = mkSimpleWidget (WidgetMarginXY 20 10) $ defNoChildrenFns{
        onCreate = (\widget -> notifyParentOnSizeChangedAndMarkForRedraw widget $ V2 0 160)
        ,onDraw=(\widget canvas -> do
                    canvasRect <- getCanvasRect widget
                    drawStretchedTextureR canvas "snapshot_00.41.57.jpg" Nothing canvasRect
                )}
 
mkExampleTextGrid :: WidgetInit SimpleWidget
mkExampleTextGrid = mkSimpleWidget (WidgetMarginXY 20 10) $ defNoChildrenFns{
        onCreate = (\widget -> notifyParentOnSizeChangedAndMarkForRedraw widget $ V2 0 (-1))
        ,onDraw=drawFn}
  where drawFn widget canvas = do
            canvasRect@(   SDL.Rectangle (P (V2 l t)) (V2 w h)) <- getCanvasRect widget
            setColor canvas $ grayColor 200
            fillRect canvas canvasRect
            fnt <- getFont canvas ""
            let dx = 30
                dy = 20
                txtColor = (V4 0 100 0 0)
                txtFill r y =
                    let txtRow c x = when (x < w) $ do
                                drawStr canvas fnt txtColor (P (V2 x y)) [c,r]
                                txtRow (succ c) (x+dx)
                    in when (y < h) $ do
                        txtRow '0' l
                        txtFill (succ r) (y+dy)
            txtFill '0' t
 
main :: IO ()
main = runGUI defSkin [GuiFontDef "" "PTM55F.ttf" 14] $ \gui _ -> do
    win <- newWindow gui "GUI : vertical layout test" $ 
                       SDL.defaultWindow { SDL.windowInitialSize = V2 300 400 }
    vLayout <- (win $+) =<< mkVLayout WidgetMarginNone zero (grayColor 230)
    mapM_ (vLayout $+) [mkExampleWidgetHelloWorld, mkExampleWidgetPicture, mkExampleTextGrid]