list - Haskell:制作一副纸牌

Question

我是 Haskell 的新手，在使用递归制作一副纸牌时遇到了问题。

我有所有这些定义:

data Suit = Club | Diamond | Heart | Spade

data Value = Two | Three | Four | Five | Six | Seven
              | Eight | Nine | Ten | Jack | Queen
              | King | Ace

type Card = (Suit, Value)
type Deck = [Card]

instance Show Suit where
   show Club = "Club"
   show Diamond = "Diamond"
   show Heart = "Heart"
   show Spade = "Spade"

instance Show Value where
  show Two = "Two"
  show Three = "Three"
  show Four = "Four"
  show Five = "Five"
  show Six = "Six"
  show Seven = "Seven"
  show Eight = "Eight"
  show Nine = "Nine"
  show Ten = "Ten"
  show Jack = "Jack"
  show Queen = "Queen"
  show King = "King"
  show Ace = "Ace"

我正在尝试编写一个函数

makeDeck :: Deck

它按照给定数据的顺序返回卡片列表，因此 (Club, Two - Ace), (Diamond, Two-Ace) 等。

我想使用递归来做到这一点，这就是我遇到这么多困难的原因。

任何帮助将不胜感激。

谢谢!

Answer 1

这不使用递归，但更规范的方法是:

添加 deriving Enum到西装和值(value)的定义，然后:

makeDeck :: Deck
makeDeck = [(suit, value) | suit <- [Club..Spade], value <- [Two..Ace]]

或者，提供所有花色和值的完整定义列表，而不是使用 Enum .