# Pastebin MCWdxUyf
memo' :: forall t a. Grouping t => (t -> a) -> IO (t -> IO a)
memo' t2a = do
  output <- newIORef (error "you done goofed")
  f <- getGroup (grouping @t) \(t2a -> a) -> do
    writeIORef output a
    return \_ -> writeIORef output a
  return \t -> f t t *> readIORef output