Hi,
I am trying out existential type, some sample code works well. Well,
my own code could not be compiled with message:
Grid.hs:45:11:
Kind error: `GridWidget' is applied to too many type arguments
In the type `GridWidget widget'
In the type `(GridWidget widget) -> (widget -> t) -> t'
In the type signature for `liftGW':
liftGW :: (GridWidget widget) -> (widget -> t) -> t
The code is:
{-# OPTIONS -fglasgow-exts #-}
module Grid where
import Graphics.UI.Gtk
data GridWidgetType = GridLabel
| GridTextView
data GridWidget = forall widget. (WidgetClass widget) => GridWidget widget
--GWLabel Label
-- | GWTextView TextView
gridNew defaultWidget = do
self <- fixedNew
-- gw <- gridWidgetNew defaultWidget
-- gridAddWidget self gw (0, 0)
-- self `on` realize $ do
-- (ww, wh) <- liftGW gw widgetGetSize
-- (w, h) <- widgetGetSize self
-- mapM_ (\x ->
-- mapM_ (\y -> do
-- gw <- gridWidgetNew defaultWidget
-- liftGW gw $ \gw -> fixedPut self gw (x * ww,
y * wh)
-- ) [0..floor (h / wh)]
-- ) [0..floor (w / ww)]
return self
-- gridSetWidget self (x, y) widget = do
-- w <- gridGetWidget self (x, y)
-- if w == widget
-- then return ()
-- else do
-- (w, h) <- widgetGetSize w
-- gw <- gridWidgetNew widget
-- fixedPut self gw (x * w, y * h)
-- widgetDestroy w
-- gridWidgetNew GridLabel = labelNew Nothing >>= return . GW
-- gridWidgetNew GridTextView = textViewNew >>= return . GW
-- gridAddWidget grid (GWLabel label) (x, y) = fixedPut grid label (x,
y)
-- gridAddWidget grid (GWTextView textView) (x, y) = fixedPut grid
textView (x, y)
liftGW :: (GridWidget widget) -> (widget -> t) -> t
liftGW (GridWidget label) f = f label
liftGW (GridWidget textView) f = f textView
--
竹密岂妨流水过
山高哪阻野云飞
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