{-# LANGUAGE FlexibleContexts #-}
{-# LANGUAGE LambdaCase #-}
{-# LANGUAGE RecordWildCards #-}
{-# LANGUAGE TypeApplications #-}
-- | A simple application architecture style inspired by PureScript's Pux
-- framework.
module GI.Gtk.Declarative.App.Simple
( App(..)
, AppView
, Transition(..)
, run
, runLoop
)
where
import Control.Concurrent
import qualified Control.Concurrent.Async as Async
import Control.Exception ( SomeException,
Exception,
catch,
finally,
throwIO)
import Control.Monad
import Data.Typeable
import qualified GI.Gdk as Gdk
import qualified GI.GLib.Constants as GLib
import qualified GI.Gtk as Gtk
import GI.Gtk.Declarative
import GI.Gtk.Declarative.EventSource
import GI.Gtk.Declarative.State
import Pipes
import qualified Pipes.Prelude as Pipes
import Pipes.Concurrent
import System.Exit
import System.IO
-- | Describes an state reducer application.
data App window state event =
App
{ update :: state -> event -> Transition state event
-- ^ The update function of an application reduces the current state and
-- a new event to a 'Transition', which decides if and how to transition
-- to the next state.
, view :: state -> AppView window event
-- ^ The view renders a state value as a window, parameterized by the
-- 'App's event type.
, inputs :: [Producer event IO ()]
-- ^ Inputs are pipes 'Producer's that feed events into the application.
, initialState :: state
-- ^ The initial state value of the state reduction loop.
}
-- | The top-level widget for the 'view' function of an 'App',
-- requiring a GTK+ 'Window'.
type AppView window event = Bin window event
-- | The result of applying the 'update' function, deciding if and how to
-- transition to the next state.
data Transition state event =
-- Transition to the given state, and with an IO action that may return a
-- new event.
Transition state (IO (Maybe event))
-- | Exit the application.
| Exit
-- | An exception thrown by the 'run' function when gtk's main loop exits
-- before event/state handling which should never happen but can be caused
-- by user code calling 'Gtk.mainQuit'
data GtkMainExitedException =
GtkMainExitedException String deriving (Typeable, Show)
instance Exception GtkMainExitedException
-- | Initialize GTK and run the application in it. This is a
-- convenience function that is highly recommended. If you need more
-- flexibility, e.g. to set up GTK+ yourself, use 'runLoop' instead.
run
:: Gtk.IsBin window
=> App window state event -- ^ Application to run
-> IO state
run app = do
assertRuntimeSupportsBoundThreads
void $ Gtk.init Nothing
-- If any exception happen in `runLoop`, it will be re-thrown here
-- and the application will be killed.
main <- Async.async Gtk.main
runLoop app `finally` (Gtk.mainQuit >> Async.wait main)
-- | Run an 'App'. This IO action will loop, so run it in a separate thread
-- using 'async' if you're calling it before the GTK main loop.
-- Note: the following example take care of exception raised in 'runLoop'.
--
-- @
-- void $ Gtk.init Nothing
-- main <- Async.async Gtk.main
-- runLoop app `finally` (Gtk.mainQuit >> Async.wait main)
-- @
runLoop :: Gtk.IsBin window => App window state event -> IO state
runLoop App {..} = do
let firstMarkup = view initialState
events <- newChan
(firstState, subscription) <- do
firstState <- runUI (create firstMarkup)
runUI (Gtk.widgetShowAll =<< someStateWidget firstState)
sub <- subscribe firstMarkup firstState (publishEvent events)
return (firstState, sub)
Async.withAsync (runProducers events inputs) $ \inputs' -> do
Async.withAsync (wrappedLoop firstState firstMarkup events subscription) $ \loop' -> do
Async.waitEither inputs' loop' >>= \case
Left _ -> Async.wait loop'
Right state -> state <$ Async.uninterruptibleCancel inputs'
where
wrappedLoop firstState firstMarkup events subscription =
loop firstState firstMarkup events subscription initialState
-- Catch exception of linked thread and reraise them without the
-- async wrapping.
`catch` (\(Async.ExceptionInLinkedThread _ e) -> throwIO e)
loop oldState oldMarkup events oldSubscription oldModel = do
event <- readChan events
case update oldModel event of
Transition newModel action -> do
let newMarkup = view newModel
(newState, sub) <- case patch oldState oldMarkup newMarkup of
Modify ma -> runUI $ do
cancel oldSubscription
newState <- ma
sub <- subscribe newMarkup newState (publishEvent events)
return (newState, sub)
Replace createNew -> runUI $ do
Gtk.widgetDestroy =<< someStateWidget oldState
cancel oldSubscription
newState <- createNew
Gtk.widgetShowAll =<< someStateWidget newState
sub <- subscribe newMarkup newState (publishEvent events)
return (newState, sub)
Keep -> return (oldState, oldSubscription)
-- If the action returned by the update function produced an event, then
-- we write that to the channel.
-- This is done in a thread to avoid blocking the event loop.
a <- Async.async $
-- TODO: Use prioritized queue for events returned by 'update', to take
-- precendence over those from 'inputs'.
action >>= maybe (return ()) (writeChan events)
-- If any exception happen in the action, it will be reraised here and
-- catched in the thread. See the ExceptionInLinkedThread
-- catch.
Async.link a
loop newState newMarkup events sub newModel
Exit -> return oldModel
-- | Assert that the program was linked using the @-threaded@ flag, to
-- enable the threaded runtime required by this module.
assertRuntimeSupportsBoundThreads :: IO ()
assertRuntimeSupportsBoundThreads = unless rtsSupportsBoundThreads $ do
hPutStrLn
stderr
"GI.Gtk.Declarative.App.Simple requires the program to \
\be linked using the threaded runtime of GHC (-threaded \
\flag)."
exitFailure
publishEvent :: Chan event -> event -> IO ()
publishEvent mvar = void . writeChan mvar
runProducers :: Chan event -> [Producer event IO ()] -> IO ()
runProducers chan producers =
Async.forConcurrently_ producers $ \producer -> do
runEffect $ producer >-> Pipes.mapM_ (publishEvent chan)
performGC
runUI :: IO a -> IO a
runUI ma = do
r <- newEmptyMVar
runUI_ (ma >>= putMVar r)
takeMVar r
runUI_ :: IO () -> IO ()
runUI_ ma = do
tId <- myThreadId
void . Gdk.threadsAddIdle GLib.PRIORITY_DEFAULT $ do
-- Any exception in the gtk ui thread will be rethrown in the calling thread.
-- This ensure that this exception won't terminate the application without any control.
ma `catch` throwTo @SomeException tId
return False