WxHaskell and DragAndDrop

I would like to know how to use the following events handlers : dropTargetOnData, dropTargetOnDrop, dropTargetOnEnter, dropTargetOnDragOver….[1]

Could you check if my current believes are corrects :

• From wx Widgets/ wxPython [2] / [3] / [4] it looks like they need to be used to manage DragAndDrog for non trivial examples.
• they are not actionable via an existing event like "on drag", etc..
• I tried and create my own event. but it does not get "activated". [7]
• besides, from the signatures [1], these look like being activated on DropTarget, unlike other events on Reactive/ Windows/Controls . Is It Correct ?

• Heinrich created its own events "onText", (in reactive-Banana) but this is on a Control. [6]

• Could someone confirm these events effectively worked for them in WxHaskell, and maybe hint how to do that

  [1]: from Graphics.UI.WXCore.Events , line 1933 onwards

  Set an event handler that is called when the drop target can be filled with data. This function require to use 'dropTargetGetData' in your event handler to fill data. dropTargetOnData :: DropTarget a -> (Point -> DragResult -> IO DragResult) -> IO () ...

  -- | Set an event handler for an drop command in a drop target. dropTargetOnDrop :: DropTarget a -> (Point -> IO Bool) -> IO ()

  -- | Set an event handler for an enter command in a drop target. dropTargetOnEnter :: DropTarget a -> (Point -> DragResult -> IO DragResult) -> IO ()

  -- | Set an event handler for a drag over command in a drop target. dropTargetOnDragOver :: DropTarget a -> (Point -> DragResult -> IO DragResult) -> IO ()

  -- | Set an event handler for a leave command in a drop target. dropTargetOnLeave :: DropTarget a -> (IO ()) -> IO ()

[2] : http://docs.wxwidgets.org/2.8/wx_wxdroptarget.html#wxdroptargetondrop

[3] : http://wiki.wxpython.org/DragAndDrop

[4] : http://www.blog.pythonlibrary.org/2012/06/20/wxpython-introduction-to-drag-and-drop/

[5] : http://wewantarock.wordpress.com/2011/06/17/how-does-wxhaskell-event-handling-work-part-1/

[6] : https://github.com/HeinrichApfelmus/reactive-banana/blob/master/reactive-banana-wx/src/Reactive/Banana/WX.hs L 88

[7] : module Main where

import Graphics.UI.WX hiding (empty)

import Data.Maybe
import Control.Monad
import Graphics.UI.WX.Events
import Graphics.UI.WXCore.WxcClassesMZ
--import Graphics.UI.WXCore.WxcClassesAL
import Graphics.UI.WXCore.DragAndDrop
import Graphics.UI.WXCore.Events    
main
  = start dndtest
dndtest
  = do
      f      <- frame  [text := "Drag And Drop test"]
      p      <- panel  f []
      ok     <- button p [text := "Ok"]
      xinput <- textEntry p [text := "here :"] --textEntry
      yinput <- staticText p [text := "drag me"]
      zinput <- staticText p [text := "result me"]

      set f [defaultButton := ok
             ,layout := container p $
                        margin 10 $
                        column 5 [boxed "coordinates" (grid 5 5 [[label "source:", hfill $ widget yinput]
                                                                ,[label "target(focus first):", hfill $ widget xinput]
                                                                ,[label "result:", hfill $ widget zinput]
                                                                ])
                                 ,floatBottomRight $ row 5 [widget ok]]
                                 ]

      set xinput [ on enter := onEnter]

      set yinput [ ]

---------------------------------------------------------
--- meaningful stuff starts here
---------------------------------------------------------

       -- prepare the drop source : create a DataObject and associate it with the source
      textdata' <- textDataObjectCreate "text dropped"
      src <- dropSource textdata' yinput



       -- prepare the drop target: create a DataObject (placeholder here) and associate it with the target
      textdata <- textDataObjectCreate ".."
      drop <- dropTarget xinput textdata
      set drop [ on onMyDrop := showMeDrop ]  ---- <<<< I am expecting this to get fired but no ...
      -- obj create a new event on drop invoking ..
      -- and see if it is invoked

      set yinput [ on drag := onDrag src ]
      set xinput [ ] ------ <<<< I am expecting the target to react when dropped  (Its DroopedTarget i fact)
      set zinput [ on mouse := showMeE]


      set ok [ on command := close f ]
      return ()

--- this is the custom event, just a setter to fire dropTargetOnDrop. not sure at all this is the correct way.

onMyDrop = newEvent "onmyDrop" (\w -> ioError (userError ("attribute '" ++ "onmyDrop" ++ "' is write-only.")))  dropTargetOnDrop
--dropTargetOnDrop :: DropTarget a -> (Point -> IO Bool) -> IO ()
--- the rest are jsut helper to see whats going on

showMeEo = putStr "showMeEo"
showMeDrop p = do
                putStr "showMeDrop"
                return True



onDrag s p  =  do

--    dragAndDrop :: DropSource a -> DragMode -> (DragResult -> IO ()) -> IO ()
    dragAndDrop s Default (\r -> do {putStr "DnD handler called: "; putStrLn(show r); return ()})
    putStrLn "on Drag activated:"



showMeE :: EventMouse -> IO ()
showMeE (MouseMotion point mod) = putStr ""  --- discard meaningless Motion event
showMeE  e = putStrLn $ show e

--
onEnter p = putStrLn $ "on Enter:" ++ show p