ADD error message for device init

lib/Xmobar/Plugins/Bluetooth.hs

@@ -206,7 +206,12 @@ addDeviceRemovedListener state dpy adapter sys =
       old <- removeDevice state d
       forM_ old $ liftIO . removeMatch (toClient sys) . btDevSigHandler
 
-pathCallback :: MonadUnliftIO m => ObjectPath -> m () -> (ObjectPath -> m ()) -> SignalCallback m
+pathCallback
+  :: MonadUnliftIO m
+  => ObjectPath
+  -> m ()
+  -> (ObjectPath -> m ())
+  -> SignalCallback m
 pathCallback adapter dpy f [device, _] = forM_ (fromVariant device) $ \d ->
   when (adaptorHasDevice adapter d) $ f d >> dpy
 pathCallback _ _ _ _ = return ()
@@ -303,9 +308,12 @@ addAndInitDevice
   -> SysClient
   -> m ()
 addAndInitDevice state dpy device client = do
-  sh <- addDeviceListener state dpy device client
+  res <- addDeviceListener state dpy device client
-  -- TODO add some intelligent error messages here
+  case res of
-  forM_ sh $ \s -> initDevice state s device client
+    Just handler -> initDevice state handler device client
+    Nothing -> logError $ "could not initialize device at path " <> device_
+  where
+    device_ = displayWrapQuote $ displayObjectPath device
 
 initDevice
   :: (MonadReader env m, HasLogFunc env, MonadUnliftIO m)