状态单子：用一种模式交换另一种模式？
因此，我正在用 Haskell 编写一个游戏，并将玩家的回合表示为一系列与各个回合阶段相关的状态改变函数。最初，这看起来像：
let game' = phase1 game
game'' = phase2 game'
-- etc.
国家独子的主要候选人，对吧？这导致更优雅：
do
phase1
phase2
-- etc.
但是，似乎我必须更改 phase1、phase2 等，以从样板“状态获取”步骤开始：
phase1 = get >>= \game -> -- ...
I'我希望有一种方法可以将其抽象出来，这样我就可以避免调用者和被调用者都出现样板。我只是太新了，不知道这种方式是什么（这是我的第一个真正的 Haskell 项目）。有什么建议吗？
So I'm writing a game in Haskell, and I'm expressing a player's turn as a series of state-altering functions that correlate to various turn phases. Originally, this looks something like:
let game' = phase1 game
game'' = phase2 game'
-- etc.
Prime candidate for State monadosity, right? This leads to the more elegant:
do
phase1
phase2
-- etc.
However, then it seems like I have to change phase1, phase2, et al to begin with a boilerplate "State getting" step:
phase1 = get >>= \game -> -- ...
I'm hoping there's a way to abstract this out, so I can avoid boilerplate on both the caller and the callee. I'm just too new to know what this way is (this is my first real Haskell project). Any advice?
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嗯，它还不是很单调。这是 Endo 幺半群。这会导致更优雅
，并且每个阶段都会被写入：
如果您需要在每个阶段中返回一些附加数据以及新状态，那么您将转向 monad。在这种情况下，一个简单的函数将使您的样板更容易忍受：
然后编写一个阶段：
但是如果您想使用状态，您可能必须给它一个名称（除非您可以通过以下方式欺骗pointfreeness：使用 获取 或 < a href="http://hackage.haskell.org/package/data-accessor" rel="nofollow noreferrer">data-accessor），在这种情况下，你不能得到比函数更简洁的东西和一个 lambda。
Well, it's not quite monadosic yet. This is a prime candidate for an Endo monoid. This leads to the more elegant
And each phase is written:
You would move to a monad if you needed to return a some additional data along with the new state in each phase. In that case a simple function will make your boilerplate more tolerable:
And then a phase is written:
But if you want to use the state, you are probably going to have to give it a name (unless you can finagle pointfreeness by, say, using gets or data-accessor), and in that case you can't get much terser than a function and a lambda.