Can't go above root

app/Main.hs

@@ -16,6 +16,7 @@ import           System.IO.Error
 import           Brick
 import           Brick.Widgets.Edit
 import           Graphics.Vty
+import           Data.List              ( isPrefixOf )
 import           Data.List.Extra        ( sortOn
                                         , (!?))
 import qualified Data.Ord
@@ -35,7 +36,10 @@ listSym dir = filterM pathIsSymbolicLink =<< listContents dir
 handlePermissionError :: IOError -> IO Integer
 handlePermissionError e = if isPermissionError e then pure 0 else ioError e
 
-getSizeSubpaths :: FilePath -> IORef (IOHashMap FilePath [(FilePath, Integer)]) -> IO [(FilePath, Integer)]
+getSizeSubpaths ::
+  FilePath ->
+  IORef (IOHashMap FilePath [(FilePath, Integer)]) ->
+  IO [(FilePath, Integer)]
 getSizeSubpaths x i = do
   memo <- readIORef i
   val <- lookup x memo
@@ -64,11 +68,12 @@ data ScrollDirection where
 
 data AppS = AppS
   {
-    appCWD :: FilePath
-  , appCursor :: Int
-  , appFocus :: Maybe FilePath
+    appCWD      :: FilePath
+  , appCursor   :: Int
+  , appFocus    :: Maybe FilePath
   , appSubFiles :: [(FilePath, Integer)]
-  , appMemo  :: IORef (IOHashMap FilePath [(FilePath, Integer)])
+  , appMemo     :: IORef (IOHashMap FilePath [(FilePath, Integer)])
+  , appRoot     :: FilePath
   }
 
 app :: App AppS e ()
@@ -150,12 +155,14 @@ overDir :: AppS -> IO AppS
 overDir s = do
   changeWorkingDirectory ".."
   a <- getWorkingDirectory
-  changeDir $ s {
-                  appCWD = a
-                , appCursor = 0
-                , appFocus = pure a
-                , appSubFiles = []
-                }
+  if a `isPrefixOf` appRoot s && a /= appRoot s then
+    pure s else
+    changeDir $ s {
+                    appCWD = a
+                  , appCursor = 0
+                  , appFocus = pure a
+                  , appSubFiles = []
+                  }
 
 scroll :: ScrollDirection -> AppS -> AppS
 scroll d s = s {
@@ -194,7 +201,10 @@ eventHandler (VtyEvent (EvKey k _)) = do
 eventHandler (VtyEvent (EvResize _ _)) = pure ()
 eventHandler _ = undefined
 
-initialState :: FilePath -> IORef (IOHashMap FilePath [(FilePath, Integer)]) -> AppS
+initialState ::
+  FilePath ->
+  IORef (IOHashMap FilePath [(FilePath, Integer)]) ->
+  AppS
 initialState f i =
   AppS {
           appCWD = f
@@ -202,6 +212,7 @@ initialState f i =
         , appFocus = pure f
         , appSubFiles = []
         , appMemo = i
+        , appRoot = f
         }
 
 main :: IO ()