Haskell 如何获取元组列表中两种不同数据类型之间的差异？

Question

我想知道是否有一种简单的方法可以在元组列表中获得 Haskell 中两种数据类型之间的差异。

假设我定义了 2 种数据类型：

type Name = String
type Age = String
type Color = String
type Size = Int 

data Animal = Animal Name Age Color Size
data Cat = Cat Name Age Color

然后，我想获得一个元组列表，其中包含除猫以外的所有动物。该功能类似于：

getAnimalsButCats :: [Animal] -> [Cat] -> [(Name, Age, Color)]
getAnimalsButCats [(Animal name age color _)] [(Cat nameC ageC colorC)] = //diff between [Animal] and [Cat]

Answer 1

你可能想要这样的东西

type Name = String
type Age = String
type Color = String
type Size = Int

data AnimalKind = Cat | Dog | Horse | Bird
data Animal = Animal AnimalKind Name Age Color Size

getAnimalsButCats :: [Animal] -> [(Name, Age, Color)]
getAnimalsButCats [] = []
-- Skip cats
getAnimalsButCats ((Animal Cat _ _ _ _):xs) = getAnimalsButCats xs
-- Save name, age, color for any other animal
getAnimalsButCats ((Animal _ name age color _): xs) = (name, age, color) : (getAnimalsButCats xs)

Haskell 如何获取元组列表中两种不同数据类型之间的差异？

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