-- A little demo program that was proposed on gui@haskell.org to compare
-- toolkit APIs.  This is a version for the plain Gtk+HS API.
--
-- There is a single button, which, when clicked once, changes the display
-- and, when clicked a second time, terminates the application.
--

import Monad
import IOExts     (IORef, newIORef, readIORef, writeIORef)

import Gtk hiding (init, main)
import qualified
       Gtk        (init, main)

main :: IO ()
main = 
  do
    Gtk.init Nothing

    -- create a new window with a box to pack widgets vertically
    --
    window <- windowNew WindowToplevel
    vbox   <- vBoxNew False 10
    window `containerAdd` vbox

    -- terminate if the window disappears
    --
    window `signalConnect` WidgetDeleteEventHandler 
      (\_ _ -> mainQuit >> return False)

    -- add the label and button to the box
    --
    label  <- labelNew " Hello World "
    button <- buttonNewWithLabel " Bye "
    butlbl <- liftM fromWidget $ binGetChild button :: IO Label
    boxPackStart vbox label  True True 2
    boxPackStart vbox button True True 2

    -- create a stateful signal handler for the button
    --
    clickedAlreadyRef <- newIORef False
    button `signalConnect` ButtonClickedHandler 
      (\_ -> do 
	       clickedAlready <- readIORef clickedAlreadyRef
	       if clickedAlready
	         then 
		   mainQuit
		 else do
		   labelSetText label  " Goodbye "
		   labelSetText butlbl " Exit "
		   writeIORef clickedAlreadyRef True)

    -- display the window and enter the event loop
    --
    widgetShowAll window
    Gtk.main