refB :: Ref a -> Event void -> UI (B a)
refB r ev = do
  (e,h) <- newEvent
  onEvent ev $ \_ -> do
    a' <- readRef r
    h a'
  a <- readRef r
  stepper a e
refB :: Ref a -> Event void -> UI (B a)
refB r ev = do
  (e,h) <- newEvent
  onEvent ev $ \_ -> do
    a' <- readRef r
    h a'
  a <- readRef r
  stepper a e
refB r ev = do
  (e,h) <- newEvent
  onEvent ev $ \_ -> do
    a' <- readRef r
    h a'
  a <- readRef r
  stepper a e