设计一元类型
我需要一些帮助来设计一个单子数据类型，我似乎很难理解这个想法，但我非常清楚我想要什么。在这方面，只有类型检查器似乎需要一些说服力。
我想要的是一些可以是 monad 的数据类型Primitive。其功能基本上是绘制基元，我希望能够将它们组合起来，并且组合也是基元，就像库 parsec 中的 Parser 类型一样。但实际的绘制必须使用IO monad 来完成。
顺便说一句，我还有一个类 Drawable a ，如下所示：
class Drawable a where
draw :: (MonadIO m) => Pos -> a -> m ()
并且我当然希望每个 Primitive 都是可绘制的。感谢您的任何意见。
I'd need some help to design a monadic datatype, I seem to have trouble wrapping my head around the idea, but I pretty definitely know what I want. Only the type checker seems to require some persuading in that matter.
What I want is some datatype Primitive that can be a monad. Functions of that are basically drawing primitives, and I want to be able to combine them and the combinations being primitives as well, much like the Parser type in the library parsec. But the actual drawing has to be done with an IO monad.
Incidentally, I also have a class Drawable a like this:
class Drawable a where
draw :: (MonadIO m) => Pos -> a -> m ()
And I want every Primitive of course to be drawable. Am thankful for any input.
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评论（1）
我不明白为什么你认为这应该是一个单子。它有什么一元的？
你应该先设计你想要的API，然后逐步思考如何抽象它。
顺便说一句，Brent 的图表库有一个非常好的组合 API，可以提供一些好主意： http://byorgey.wordpress.com/2008/04/30/new-haskell-diagrams-library/
I don't understand why you think this should be a monad. What's monadic about it?
You should design the API you want first, and incrementally think about how to abstract it.
Incidentally, Brent's diagrams library has a very nice compositional API that could provide some good ideas: http://byorgey.wordpress.com/2008/04/30/new-haskell-diagrams-library/