API: handleEvent now runs in EventM

programs/DialogDemo.hs

@@ -31,7 +31,7 @@ appEvent d ev =
     case ev of
         V.EvKey V.KEsc [] -> M.halt d
         V.EvKey V.KEnter [] -> M.halt d
-        _ -> M.continue $ T.handleEvent ev d
+        _ -> M.continue =<< T.handleEvent ev d
 
 initialState :: D.Dialog Choice
 initialState = D.dialog "dialog" (Just "Title") (Just (0, choices)) 50

programs/EditDemo.hs

@@ -61,7 +61,9 @@ appEvent st ev =
     case ev of
         V.EvKey V.KEsc [] -> M.halt st
         V.EvKey (V.KChar '\t') [] -> M.continue $ switchEditors st
-        _ -> M.continue $ st & currentEditorL st %~ T.handleEvent ev
+        _ -> do
+            e <- T.handleEvent ev (st ^. currentEditorL st)
+            M.continue $ st & currentEditorL st .~ e
 
 initialState :: St
 initialState =

programs/ListDemo.hs

@@ -58,7 +58,7 @@ appEvent l e =
 
         V.EvKey V.KEsc [] -> M.halt l
 
-        ev -> M.continue $ T.handleEvent ev l
+        ev -> M.continue =<< T.handleEvent ev l
 
 listDrawElement :: Bool -> Int -> Widget
 listDrawElement sel i =

src/Brick/Types.hs

@@ -69,7 +69,7 @@ data Padding = Pad Int
 -- | The class of types that provide some basic event-handling.
 class HandleEvent a where
     -- | Handle a Vty event
-    handleEvent :: Event -> a -> a
+    handleEvent :: Event -> a -> EventM a
 
 -- | The monad in which event handlers run.
 type EventM a = StateT EventState IO a

src/Brick/Widgets/Dialog.hs

@@ -68,9 +68,9 @@ suffixLenses ''Dialog
 instance HandleEvent (Dialog a) where
     handleEvent ev d =
         case ev of
-            EvKey (KChar '\t') [] -> nextButtonBy 1 d
-            EvKey KBackTab [] -> nextButtonBy (-1) d
-            _ -> d
+            EvKey (KChar '\t') [] -> return $ nextButtonBy 1 d
+            EvKey KBackTab [] -> return $ nextButtonBy (-1) d
+            _ -> return d
 
 -- | Create a dialog.
 dialog :: Name

src/Brick/Widgets/Edit.hs

@@ -72,7 +72,7 @@ instance HandleEvent Editor where
                   EvKey KRight [] -> Z.moveRight
                   EvKey KBS [] -> Z.deletePrevChar
                   _ -> id
-        in applyEdit f ed
+        in return $ applyEdit f ed
 
 -- | Construct an editor.
 editor :: Name

src/Brick/Widgets/List.hs

@@ -59,7 +59,7 @@ data List e =
 suffixLenses ''List
 
 instance HandleEvent (List e) where
-    handleEvent e theList = f theList
+    handleEvent e theList = return $ f theList
         where
             f = case e of
                   EvKey KUp [] -> listMoveUp