我正在尝试像这样声明 MonadPlus 接口:
I'm trying to declare MonadPlus interface like that:
module NanoParsec.Plus %access public export interface Monad m => MonadPlus m where zero : m a plus : m a -> m a -> m a但是有一个错误:
| 5 | interface Monad m => MonadPlus m where | ~~~~~~~ When checking type of constructor of NanoParsec.Plus.MonadPlus#Monad m: When checking argument m to type constructor Prelude.Monad.Monad: Type mismatch between Type (Type of m) and Type -> Type (Expected type)我做错了什么?如何解决这个问题?Idris 没有自己的 MonadPlus 接口是对的吗?如果是,为什么?
What I'm doing wrong? How to fix this? Am I right that Idris has no its own MonadPlus interface? If so, why?
推荐答案在Idris中,当你定义一个接口时,参数类型默认为Type,所以MonadPlus m这里是 MonadPlus (m: Type) 的缩写,Idris 将 m 视为 Type.这当然不符合约束 Monad m,它需要 Type ->输入.
In Idris, when you define an interface, the parameter type defaults to Type, so MonadPlus m here is short for MonadPlus (m: Type), and Idris treats m as a Type. This of course doesn't fit with the constraint Monad m, which expects a Type -> Type.
如果你想参数化其他东西,你必须明确,比如
You have to be explicit if you want to parametrize over something else, like
interface Monad m => MonadPlus (m: Type -> Type) where zero : m a plus : m a -> m a -> m aMonadPlus 本身超出了我的知识范围,所以我不知道它在 Idris 中是否存在.
MonadPlus itself is beyond my knowledge so I don't know about its presence, or lack thereof, in Idris.
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无法声明受 Monad 约束的 MonadPlus 接口
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