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Lớp kiểu MonadState class Monad m => MonadState s m | m -> s where layTrangThai :: m s layTrangThai = trangThai (\s -> (s, s)) datTrangThai :: s -> m () datTrangThai s = trangThai (\_ -> ((), s)) trangThai :: (s -> (a, s)) -> m a trangThai f = do s <- layTrangThai let ~(a, s') = f s ...