[Haskell-cafe] Re: StateT IO Action on `onKeyPress`

[Andy Stewart]

Hi Ryan,

Ryan Ingram <ryani.spam at gmail.com> writes:

> Hi Andy.
>
> The GTK bindings use IO for their callbacks, not any custom monad like
> your WindowListT.
>
> I suggest, instead of StateT s IO a, you use ReaderT (IORef s) IO a:
>
> putR :: s -> ReaderT (IORef s) IO ()
> putR s = do
>     r <- ask
>     liftIO $ writeIORef r s
>
> getR :: ReaderT (IORef s) IO s
> getR = ask >>= liftIO . readIORef
>
> Otherwise, there are techniques to use an IORef to hold onto the state
> while calling into IO (which might make callbacks), and then read it
> back out and put it in the state while running your action.  But it's
> simpler to just switch to ReaderT
I'm curious another techniques that use IORef hold on state.

Can you implement a simple example that make my code pass `onKeyPress`? 

Thanks!

  -- Andy

>
>   -- ryan
>
> On Sun, May 3, 2009 at 8:27 AM, Andy Stewart <lazycat.manatee at gmail.com> wrote:
>> Hi all,
>>
>> I have a function named `keymapTest` need moand state WindowListT, and
>> WindowListT is `type WindowListT = StateT WindowList IO`.
>>
>> when i add "(\event -> keymapTest winList event >> return False)" after
>> `onKeyPress` for handle key press event, i got GHC error:
>>
>> Manatee.hs:57:58:
>>    Couldn't match expected type `IO a'
>>           against inferred type `WindowListT Bool'
>>    In the first argument of `(>>)', namely `keymapTest winList event'
>>    In the expression: keymapTest winList event >> return False
>>    In the second argument of `onKeyPress', namely
>>        `(\ event -> keymapTest winList event >> return False)'
>>
>> So function `onKeyPress` just accept *one* IO-action?
>> Have a way to fix above problem?
>>
>> Any help?
>>
>> Thanks!
>>
>>  -- Andy
>>
>> Below is source code of Manatee.hs file.
>>
>> ------------------------------> Manatee.hs start   <------------------------------
>> module Main where
>>
>> import Text.Printf
>> import Data.Monoid
>> import Data.List
>> import Data.Maybe
>> import Control.Monad
>> import Control.Monad.State
>> import Control.Applicative
>>
>> import Data.IORef
>>
>> import Graphics.UI.Gtk hiding (Window, windowNew, get)
>> import Graphics.UI.Gtk.SourceView
>> import Graphics.UI.Gtk.Abstract.Widget
>>
>> import Manatee.Event
>> import Manatee.Buffer
>> import Manatee.WindowList
>> import Manatee.Pane
>> import Manatee.Statusbar
>> import Manatee.Utils
>> import Manatee.Window
>>
>> import qualified Data.Set as Set
>> import qualified Graphics.UI.Gtk.Windows.Window as W
>> import qualified Graphics.UI.Gtk.Gdk.Events as E
>>
>> main :: IO ()
>> main = do
>>  -- Init.
>>  initGUI
>>
>>  -- Root frame.
>>  rootFrame <- W.windowNew
>>  rootFrame `onDestroy` mainQuit  -- quit main loop when root frame close
>>
>>  -- Root frame status.
>>  windowFullscreen rootFrame   -- fullscreen
>>
>>  -- Windows list.
>>  let windowsList = WindowList 0 Set.empty
>>
>>  evalStateT (do
>>               -- Window 1
>>               window1 <- windowNewWithBuffer DTop "test"
>>               liftIO $ containerAdd rootFrame $ windowPaned window1
>>
>>               (window2, window3) <- windowSplitVertically window1
>>
>>               (window4, window5) <- windowSplitHorizontally window3
>>
>>               winList <- windowListGetList
>>               liftIO $ rootFrame `onKeyPress` (\event -> keymapTest winList event >> return False)
>>
>>               -- Handle window content synchronous.
>>               windowHandleSynchronous
>>               ) windowsList
>>
>>  -- Loop
>>  widgetShowAll rootFrame       -- display all widget
>>  mainGUI
>>
>> keymapTest :: [Window] -> E.Event -> WindowListT Bool
>> keymapTest winList event = do
>>  window <- liftIO $ windowFindFocus winList
>>  case window of
>>    Just x -> handleKeyPress x event
>>    Nothing -> return False
>>
>> handleKeyPress :: Window -> E.Event -> WindowListT Bool
>> handleKeyPress window ev = do
>>  liftIO $
>>         case eventTransform ev of
>>           Nothing -> return False
>>           Just e -> do
>>             let display = statusbarOutputSubitemSetText $ paneStatusbar $ windowPane $ window
>>                 eventName = eventGetName e
>>             case eventName of
>>                -- Window commands.
>>                "M-t" -> display "windowSplitVertically"
>>                -- "M-t" -> windowSplitVertically window >> return False
>>                _ -> display $ printf "%s undefined." eventName
>> ------------------------------> Manatee.hs end   <------------------------------
>>
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