Haskell 将衍生过孔与幻像类型一起使用
很抱歉我的复述太长了,但我没能把它缩短。以下代码在最后一行之前编译良好:Haskell 将衍生过孔与幻像类型一起使用,haskell,deriving,coerce,Haskell,Deriving,Coerce,很抱歉我的复述太长了,但我没能把它缩短。以下代码在最后一行之前编译良好: {-# LANGUAGE RankNTypes #-} {-# LANGUAGE MultiParamTypeClasses, FlexibleInstances, UndecidableInstances #-} {-# LANGUAGE DerivingVia, DerivingStrategies, StandaloneDeriving #-} {-# LANGUAGE ScopedTypeVariables #-}
{-# LANGUAGE RankNTypes #-}
{-# LANGUAGE MultiParamTypeClasses, FlexibleInstances, UndecidableInstances #-}
{-# LANGUAGE DerivingVia, DerivingStrategies, StandaloneDeriving #-}
{-# LANGUAGE ScopedTypeVariables #-}
module Repro where
import Prelude hiding ((+))
class (Additive a) where
(+) :: a -> a -> a
data Vector2D u = Vector2D {
x :: u,
y :: u
}
addVector2 :: (Additive a) => Vector2D a -> Vector2D a -> Vector2D a
addVector2 Vector2D { x = x1, y = y1 } (Vector2D { x = x2, y = y2 }) =
Vector2D { x = x1 + x2, y = y1 + y2 }
instance (Additive a) => Additive (Vector2D a) where
(+) = addVector2
newtype Phantom1 d a = Phantom1 (Vector2D a) --Axial
deriving via (Vector2D a) instance forall d . (Additive a) => (Additive (Phantom1 d a))
data Via a b = Via a
class IsoEvidence a b where
convertTo :: a -> b
convertFrom :: b -> a
instance forall a b . (IsoEvidence a b, Additive b) => (Additive (Via a b)) where
(Via x) + (Via y) = Via $ convertFrom $ (convertTo x :: b) + (convertTo y :: b)
newtype Phantom2 d a = Phantom2 (Vector2D a) --Offset
instance (IsoEvidence (Phantom1 d a) (Phantom2 d a)) where
convertTo (Phantom1 x) = Phantom2 x
convertFrom (Phantom2 x) = Phantom1 x
deriving via (Via (Phantom2 d a) (Phantom1 d a))
instance (Additive a, IsoEvidence (Phantom1 d a) (Phantom2 d a)) =>
(Additive (Phantom2 d a))
之后,我得到以下错误:
- 无法匹配类型
与Vector2D a的表示形式
Via(phantom2da)(phantom1da)
我做错了什么?
通过新类型派生,但您编写了
data Via a b = Via a -- should be newtype
我是个白痴。谢谢你。