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

Ryan Ingram writes:

Something like this:

-- Replaces "runStateT" for callbacks that might affect the state invert :: IORef s -> StateT s IO a -> IO a invert r m = do s <- readIORef r (a, s') <- runStateT m s writeIORef r s' return a

-- Replaces "liftIO" when the action called might use "invert" revert :: IORef s -> IO a -> StateT s IO a revert r m = do s <- get writeIORef r s a <- liftIO m s' <- readIORef r put s' return a

Then you use ... `onKeyPress` (\event -> invert windowListRef (...))

I'm not sure where in your code revert is required; I don't know when WindowListT might call back into IO. If you want to be extra safe, make the IORef be a Maybe WindowList and make sure it's "Nothing" except between 'revert' and 'invert'. Result is ReaderT is cleaner and simpler.

Thanks for your help! -- Andy

-- ryan

On Mon, May 4, 2009 at 1:02 AM, Andy Stewart wrote:

...

Hi Ryan,

Ryan Ingram 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 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   <------------------------------

_______________________________________________ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe

_______________________________________________ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe