eval (Chunk (s:stats)) = do
  res <- eval s
  case stats of
    [] -> return res
    _ -> eval $ Chunk stats
eval (Chunk (s:stats)) = do
  res <- eval s
  case stats of
    [] -> return res
    _ -> eval $ Chunk stats
eval (Chunk (s:stats)) = do
  res <- eval s
  case stats of
    [] -> return res
    _ -> eval $ Chunk stats