Implement list element insertion and add demo

programs/Main.hs

@@ -37,7 +37,9 @@ appEvent :: Event -> St -> IO St
 appEvent e st =
     case e of
         EvKey KEsc [] -> exitSuccess
-        EvKey KEnter [] -> error $ editStr $ st^.stEditor
+        EvKey KEnter [] ->
+            let e = length $ listElements $ st^.stList
+            in return $ st & stList %~ listInsert 0 e
         ev -> return $ st & stEditor %~ (handleEvent ev)
                           & stList %~ (handleEvent ev)
 

src/Brick.hs

@@ -328,6 +328,20 @@ drawList l =
        vScroll (listScroll l) $
        VBox drawn <<= VPad ' '
 
+listInsert :: Int -> a -> List a -> List a
+listInsert pos e l =
+    let es = listElements l
+        newSel = case listSelected l of
+          Nothing -> 0
+          Just s -> if pos < s
+                    then s + 1
+                    else s
+        (front, back) = splitAt pos es
+    in l { listSelected = Just newSel
+         , listElements = front ++ (e : back)
+         , listScroll = vScrollToView newSel (listScroll l)
+         }
+
 class HandleEvent a where
     handleEvent :: Event -> a -> a