Allow for events to do io

src/Loop.hs

@@ -23,7 +23,7 @@ setupLoop
     -> (world -> IO ())    -- ^ Function for cleaning up parameters, applied when exiting loop.
     -> IO world             -- ^ Initial simulation state.
     -> (world -> IO world)   -- ^ update, called once per frame. Allows for side effects such as rendering.
-    -> (world -> Event -> Maybe world)
+    -> (world -> Event -> IO (Maybe world))
                             -- ^ SDL Event handling, once per frame. Evaluating 'Nothing' exits the loop.
     -> IO ()
 setupLoop spf (xSize,ySize) winpos paramCleanup ioStartWorld sideEffects eventFn = do 
@@ -43,7 +43,7 @@ doLoop
     :: Int      -- ^ target msec per frame
     -> Window   -- ^ The SDL window.
     -> (world -> IO world) -- ^ simulation update. 
-    -> (world -> Event -> Maybe world) -- ^ SDL Event handling.
+    -> (world -> Event -> IO (Maybe world)) -- ^ SDL Event handling.
     -> world    -- ^ Current simulation state.
     -> IO ()
 doLoop 
@@ -70,13 +70,17 @@ doLoop
         Nothing -> return ()
 -- | Handle quit events in a manner to exit the loop. Other events handled as
 -- determined by the custom function, although resize events also change the viewport.
-applyEventIO :: (world -> Event -> Maybe world) -> Maybe world -> Event -> IO (Maybe world)
+applyEventIO :: (world -> Event -> IO (Maybe world)) -> Maybe world -> Event -> IO (Maybe world)
 applyEventIO fn mw e = case eventPayload e of
     QuitEvent           -> return Nothing
     WindowClosedEvent _ -> return Nothing
     WindowSizeChangedEvent WindowSizeChangedEventData {windowSizeChangedEventSize = V2 x y}
-                        -> GL.viewport $= (GL.Position 0 0,GL.Size x y) >> return (mw >>= \w -> fn w e)
-    _                   -> return $ mw >>= flip fn e
+                        -> (GL.viewport $= (GL.Position 0 0,GL.Size x y)) >> mupdate
+    _                   -> mupdate
+  where
+    mupdate = case mw of
+        Nothing -> return Nothing
+        Just w  -> fn w e
 -- | Create an OpenGL SDL window configuration with a given x and y size.
 winConfig :: Int -> Int -> Maybe (Int, Int) -> WindowConfig
 winConfig x y winpos = defaultWindow