Flip the arguments to application event handlers to make event pattern-matching more natural

programs/CustomEventDemo.hs

@@ -29,8 +29,8 @@ drawUI st = [a]
             <=>
             (str $ "Counter value is: " <> (show $ st^.stCounter))
 
-appEvent :: CustomEvent -> St -> EventM (Next St)
-appEvent e st =
+appEvent :: St -> CustomEvent -> EventM (Next St)
+appEvent st e =
     case e of
         VtyEvent (EvKey KEsc []) -> halt st
         VtyEvent ev -> continue $ st & stLastVtyEvent .~ (Just ev)

programs/EditDemo.hs

@@ -18,8 +18,8 @@ drawUI e = [ui]
     where
         ui = center $ "Input: " <+> (hLimit 30 $ renderEditor e)
 
-appEvent :: Event -> Editor -> EventM (Next Editor)
-appEvent ev e =
+appEvent :: Editor -> Event -> EventM (Next Editor)
+appEvent e ev =
     case ev of
         EvKey KEsc [] -> halt e
         EvKey KEnter [] -> halt e

programs/ListDemo.hs

@@ -33,8 +33,8 @@ drawUI l = [ui]
                             , hCenter "Press Esc to exit."
                             ]
 
-appEvent :: Event -> List Int -> EventM (Next (List Int))
-appEvent e l =
+appEvent :: List Int -> Event -> EventM (Next (List Int))
+appEvent l e =
     case e of
         EvKey (KChar '+') [] ->
             let el = length $ l^.listElementsL

programs/Main.hs

@@ -88,8 +88,8 @@ drawUI st = [withBorderStyle bs a]
               <=> (hCenter (kw "Arrow keys" <+> " navigates the list"))
               <=> (hCenter (kw "Ctrl-Arrow keys" <+> " move the interface"))
 
-appEvent :: Event -> St -> EventM (Next St)
-appEvent e st =
+appEvent :: St -> Event -> EventM (Next St)
+appEvent st e =
     case e of
         EvKey (KChar '+') [] ->
             continue $ st & stBorderStyle %~ ((`mod` (length styles)) . (+ 1))

programs/Rogue.hs

@@ -101,8 +101,8 @@ pieceA, dumpA :: Attr
 pieceA = defAttr `withForeColor` blue `withBackColor` green
 dumpA = defAttr `withStyle` reverseVideo
 
-processEvent :: Event -> World -> EventM (Next World)
-processEvent k world = do
+processEvent :: World -> Event -> EventM (Next World)
+processEvent world k = do
     case k of
         EvKey KEsc [] -> halt world
         EvKey KLeft  [] -> continue $ movePlayer world (-1) 0

programs/SuspendAndResumeDemo.hs

@@ -24,8 +24,8 @@ drawUI st = [ui]
                   , "(Press Esc to quit or Space to ask for input)"
                   ]
 
-appEvent :: Event -> St -> EventM (Next St)
-appEvent e st =
+appEvent :: St -> Event -> EventM (Next St)
+appEvent st e =
     case e of
         EvKey KEsc [] -> halt st
         EvKey (KChar ' ') [] -> suspendAndResume $ do

src/Brick/Main.hs

@@ -76,7 +76,7 @@ data App s e =
         -- is that many widgets may request a cursor placement but your
         -- application state is what you probably want to use to decide
         -- which one wins.
-        , appHandleEvent :: e -> s -> EventM (Next s)
+        , appHandleEvent :: s -> e -> EventM (Next s)
         -- ^ This function takes an event and your application state
         -- and returns an action to be taken. Possible options are
         -- 'continue', 'suspendAndResume', and 'halt'.
@@ -130,8 +130,8 @@ simpleMain w =
 -- a halt. This is a convenience function useful as an 'appHandleEvent'
 -- value for simple applications using the 'Event' type that do not need
 -- to get more sophisticated user input.
-resizeOrQuit :: Event -> s -> EventM (Next s)
-resizeOrQuit e a =
+resizeOrQuit :: s -> Event -> EventM (Next s)
+resizeOrQuit a e =
     case e of
         EvResize _ _ -> continue a
         _ -> halt a
@@ -193,7 +193,7 @@ runVty :: Vty -> Chan e -> App s e -> s -> RenderState -> IO (Next s, RenderStat
 runVty vty chan app appState rs = do
     firstRS <- renderApp vty app appState rs
     e <- readChan chan
-    (next, scrollReqs) <- runStateT (appHandleEvent app e appState) []
+    (next, scrollReqs) <- runStateT (appHandleEvent app appState e) []
     return (next, firstRS { _scrollRequests = scrollReqs })
 
 withVty :: IO Vty -> (Vty -> IO a) -> IO a