Ivan Lazar Miljenovic writes:

Andy Stewart writes:

...

Hi all,

I have some incorrect "Read instance" make i got error "Prelude.read: no parse", and i don't know how to fix it.

newtype SerializedWindow = SerializedWindow (Maybe DrawWindow)

instance Show SerializedWindow where show _ = "SerializedWindow Nothing"

instance Read SerializedWindow where readsPrec _ str = [(SerializedWindow Nothing, idStr) | (val :: String, idStr) <- reads str]

Try using Derive or DrIFT to generate a proto-typical instance for you, and then hack that and make it neater. If you don't care about cross-compiler compatability, using ReadP rather than ReadS also results in nicer parsing code. Sorry, i haven't explain my situation.

I'm try to serialized/derserialized Gtk+ Event C struct over the network. Since DrawWindow is ForeignPtr to point C structure, and "deriving Read" nothing help. So i want build a "bogus value" -- "SerializedWindow Nothing" to fill DrawWindow pointer field. I just want got "SerializedWindow Nothing" and don't care the value that return by *reads*. Below are C struct that i want to serialized with Haskell data-type: typedef struct { GdkEventType type; GdkWindow *window; gint8 send_event; guint32 time; guint state; guint keyval; gint length; gchar *string; guint16 hardware_keycode; guint8 group; guint is_modifier : 1; } GdkEventKey; Below are my C binding that explain my purpose: ------------------------------> C binding start <------------------------------ {-# LANGUAGE ScopedTypeVariables #-} -- -*-haskell-*- #include #include "template-hsc-gtk2hs.h" -- GIMP Toolkit (GTK) GDK Serializabled Event -- -- Author : Andy Stewart -- -- Created: 01 Jul 2010 -- -- Copyright (C) 2010 Andy Stewart -- -- This library is free software; you can redistribute it and/or -- modify it under the terms of the GNU Lesser General Public -- License as published by the Free Software Foundation; either -- version 2.1 of the License, or (at your option) any later version. -- -- This library is distributed in the hope that it will be useful, -- but WITHOUT ANY WARRANTY; without even the implied warranty of -- MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU -- Lesser General Public License for more details. -- -- | -- Maintainer : gtk2hs-users\@lists.sourceforge.net -- Stability : deprecated -- Portability : portable (depends on GHC) -- module Graphics.UI.Gtk.Gdk.SerializedEvent ( -- * Types SerializedEventKey (..), -- * Methods serializedEvent, deserializeEventKey, ) where import Control.Monad.Reader (ReaderT, ask, runReaderT ) import Control.Monad.Trans (liftIO) import Data.Maybe import Data.Ord import Graphics.UI.Gtk.Gdk.DrawWindow import Graphics.UI.Gtk.Gdk.EventM import Graphics.UI.Gtk.Gdk.Keys (KeyVal) import Graphics.UI.GtkInternals import System.Glib.FFI import System.Glib.Flags data SerializedEventKey = SerializedEventKey {sEventType :: Int ,sEventWindow :: SerializedWindow ,sEventSent :: Bool ,sEventTime :: Word32 ,sEventState :: Int ,sEventKeyval :: KeyVal ,sEventLength :: Int ,sEventString :: String ,sEventKeycode :: Word16 ,sEventGroup :: Word8 ,sEventIsModifier:: Int} deriving (Show, Eq, Ord, Read) newtype SerializedWindow = SerializedWindow (Maybe DrawWindow) instance Eq SerializedWindow where (==) _ _ = True instance Ord SerializedWindow where compare _ _ = EQ instance Show SerializedWindow where show _ = "SerializedWindow Nothing" instance Read SerializedWindow where readsPrec _ str = [(SerializedWindow Nothing, idStr) | (val :: String, idStr) <- reads str] instance Storable SerializedEventKey where sizeOf _ = #{const sizeof (GdkEventKey)} alignment _ = alignment (undefined:: #gtk2hs_type gint) peek ptr = peekSerializedKey ptr poke ptr event = pokeSerializedKey ptr event serializedEvent :: EventM t SerializedEventKey serializedEvent = do ptr <- ask eType <- liftIO $ do (typ::#gtk2hs_type GdkEventType) <- #{peek GdkEventAny,type} ptr return typ case eType of #{const GDK_KEY_PRESS} -> serializedKey #{const GDK_KEY_RELEASE} -> serializedKey ty -> error ("serializedEvent: haven't handle event type " ++ show ty) serializedKey :: EventM t SerializedEventKey serializedKey = do ptr <- ask liftIO $ peekSerializedKey ptr peekSerializedKey ptr = do (typ_ ::#gtk2hs_type GdkEventType) <- #{peek GdkEventKey, type} ptr (sent_ ::#gtk2hs_type gint8) <- #{peek GdkEventKey, send_event} ptr (time_ ::#gtk2hs_type guint32) <- #{peek GdkEventKey, time} ptr (state_ ::#gtk2hs_type guint) <- #{peek GdkEventKey, state} ptr (keyval_ ::#gtk2hs_type guint) <- #{peek GdkEventKey, keyval} ptr (length_ ::#gtk2hs_type gint) <- #{peek GdkEventKey, length} ptr (keycode_ ::#gtk2hs_type guint16) <- #{peek GdkEventKey, hardware_keycode} ptr (group_ ::#gtk2hs_type guint8) <- #{peek GdkEventKey, group} ptr -- (isModifier_ ::#gtk2hs_type guint) <- #{peek GdkEventKey, is_modifier} ptr return $ SerializedEventKey {sEventType = fromIntegral typ_ ,sEventWindow = SerializedWindow Nothing -- this field need synthesize at client side ,sEventSent = toBool sent_ ,sEventTime = fromIntegral time_ -- this field need synthesize at client side ,sEventState = fromIntegral state_ ,sEventKeyval = keyval_ ,sEventLength = fromIntegral length_ ,sEventString = "" -- this filed has deprecated and should never be used ,sEventKeycode = keycode_ ,sEventGroup = group_ -- ,sEventIsModifier = isModifier_ ,sEventIsModifier = 0 } pokeSerializedKey ptr (SerializedEventKey {sEventType = typ_ ,sEventWindow = SerializedWindow window_ ,sEventSent = sent_ ,sEventTime = time_ ,sEventState = state_ ,sEventKeyval = keyval_ ,sEventLength = length_ ,sEventString = string_ ,sEventKeycode = keycode_ ,sEventGroup = group_ ,sEventIsModifier = isModifier_ }) = do #{poke GdkEventKey, type} ptr ((fromIntegral typ_) ::#gtk2hs_type GdkEventType) case (fromMaybe (DrawWindow nullForeignPtr) window_) of win_ -> withForeignPtr (unDrawWindow win_) $ \winPtr -> #{poke GdkEventKey, window} ptr winPtr #{poke GdkEventKey, send_event} ptr ((fromBool sent_) ::#gtk2hs_type gint8) #{poke GdkEventKey, time} ptr ((fromIntegral time_) ::#gtk2hs_type guint32) #{poke GdkEventKey, state} ptr ((fromIntegral state_) ::#gtk2hs_type guint) #{poke GdkEventKey, keyval} ptr (keyval_ ::#gtk2hs_type guint) #{poke GdkEventKey, length} ptr ((fromIntegral length_) ::#gtk2hs_type gint) #{poke GdkEventKey, hardware_keycode} ptr (keycode_ ::#gtk2hs_type guint16) #{poke GdkEventKey, group} ptr (group_ ::#gtk2hs_type guint8) -- | Insert DrawWindow and TimeStamp field when deserialized SerializedEventKey. deserializeEventKey :: SerializedEventKey -> DrawWindow -> (EventM t a) -> IO a deserializeEventKey event drawWindow fun = do -- We need use *client* value replace field of event. let newEvent = event {sEventWindow = SerializedWindow $ Just drawWindow ,sEventTime = currentTime} with newEvent $ \eventPtr -> runReaderT fun (castPtr eventPtr) ------------------------------> C binding end <------------------------------ -- Andy