removeHandler :: HandlerRef -> HandlerMap a -> HandlerMap a
removeHandler k hs = hs
  { handlers = Map.delete k (handlers hs)
  }
removeHandler :: HandlerRef -> HandlerMap a -> HandlerMap a
removeHandler k hs = hs
  { handlers = Map.delete k (handlers hs)
  }
removeHandler k hs = hs
  { handlers = Map.delete k (handlers hs)
  }