Question

我正在尝试从paper编译一些Haskell代码。来自paper的相关文本描述和列表如下。

文字描述

“ 我们将AFFORDANCES引入为QUALITIES的子类，并示例性地建立模型作为步步入城的一种AFFORDANCES。 QUALITIES的构造函数要求像攀爬能力这样的质量始终与其宿主一起定义。清单1中显示了AFFORDANCES和Climbability的实现。....清单1中指定的AFFORDANCES类提供了规范如何在Haskell中编写负担能力。爬坡度实现此规范。“

列出1

class (QUALITIES affordance physicalEndurant, PHYSICAL_ENDURANTS physicalEndurant) => AFFORDANCES affordance physicalEndurant

data PHYSICAL_OBJECTS step => Climbability step = Climbability step

instance QUALITIES  Climbability Step
instance AFFORDANCES Climbability Step

按现状显示清单1 缺少一些定义，这些定义已添加到清单2 中的代码中。

清单2

{-#  LANGUAGE  MultiParamTypeClasses, DatatypeContexts,FlexibleInstances #-}
data Step =  Step
class  PHYSICAL_ENDURANTS physicalEndurant where
class  PHYSICAL_OBJECTS physicalEndurant where
class  QUALITIES affordance physicalEndurant where

instance  PHYSICAL_ENDURANTS (Climbability Step) where
instance  PHYSICAL_ENDURANTS Step where

class (QUALITIES affordance physicalEndurant,PHYSICAL_ENDURANTS physicalEndurant) => AFFORDANCES affordance physicalEndurant

data PHYSICAL_OBJECTS step => Climbability step = Climbability step
-- extra arguments
instance QUALITIES  (Climbability Step) Step
instance AFFORDANCES (Climbability Step) Step

但是要编译 Listing 2 ，我必须通过向QUALITIES和AFFORDANCES实例添加额外的参数来更改 Listing 1 。我是否缺少某种方法来从文件中获取原始代码进行编译？

Answer 1

您需要告诉编译器期望类affordance和QUALITIES中的AFFORDANCES参数是类型构造函数，换句话说，具有类型* -> *而不是类型*。

如果您将{-# LANGUAGE KindSignatures #-}添加到扩展名中，则可以使用该签名对QUALITIES进行注释，其余的将跟随：

{-# LANGUAGE MultiParamTypeClasses, DatatypeContexts, FlexibleInstances, KindSignatures #-}

data Step = Step   
class PHYSICAL_ENDURANTS physicalEndurant where   
class PHYSICAL_OBJECTS physicalEndurant where   
class QUALITIES (affordance :: * -> *) physicalEndurant where 

instance PHYSICAL_ENDURANTS Step where   


class ( QUALITIES affordance physicalEndurant
      , PHYSICAL_ENDURANTS physicalEndurant
      ) => AFFORDANCES affordance physicalEndurant

data PHYSICAL_OBJECTS step => Climbability step = Climbability step    

instance QUALITIES Climbability Step      
instance AFFORDANCES Climbability Step

能将此Haskell代码编译为书面形式吗？

1 个答案: