F#类型和循环 [英] F# Types and Looping

问题描述

我正在研究F#教程，该教程创建了一副纸牌.列出了这些类型，但是我不明白如何遍历这些类型来创建整个甲板的地图.我希望做类似

I am working on an F# tutorial that creates a deck of cards. The types are listed, but I cannot understand how to loop through the types to create the map of the full deck. I expected to do something like

Foreach rank in ranks
   Foreach suit in suits
       somehow combine the two
   next suit
next rank

有没有办法做到这一点?下面是创建的类型.

Is there no way to do this? Below are the types created.

我想如果我将它们从类型更改为列表，它们可以合并，对吗?那么，类型有什么意义呢?

I think if I changed them from types to lists they could union, right? So, what's the point of types?

type suits=
    |Spade=1
    |Heart=2
    |Club=3
    |Diamond=4

type ranks=
    |ValCard of int
    |Jack 
    |Queen
    |King

type deck= Deck of ranks * suits

推荐答案

枚举是代表卡片的好选择.您可以免费在西装之间和等级之间进行比较，并轻松将枚举从/转换为int.

Enums is a good choice for representing cards. You have comparison among suits and among ranks for free, and easily convert enums from/to int.

type suit =
    | Spade = 1
    | Heart = 2
    | Club = 3
    | Diamond = 4

type rank = 
    | Ace = 1 | Two = 2 | Three = 3 | Four = 4 | Five = 5 | Six = 6 | Seven = 7 
    | Eight = 8 | Nine = 9 | Ten = 10 | Jack = 11 | Queen = 12 | King = 13

/// 'Card' is a type which represents a particular card     
type Card = Card of rank * suit

/// 'deck' is a list consisting of all cards in a full deck
let deck = [ for r in 1..13 do
               for s in 1..4 do
                 yield Card(enum<rank> r, enum<suit> s) ]

如果您要使用歧视的工会，则必须手动创建所有suit和所有rank的列表.优点是DU的模式匹配比枚举更好.

If you go for discriminated unions, you have to manually make lists of all suits and all ranks. The advantage is better pattern matching of DUs than that of enums.

type suit =
    | Spade
    | Heart
    | Club
    | Diamond

type rank = | Ace | Two | Three | Four | Five | Six | Seven 
            | Eight | Nine | Ten | Jack | Queen | King

type Card = Card of rank * suit

let private suits = [Spade; Heart; Club; Diamond]
let private ranks = [Ace; Two; Three; Four; Five; Six; Seven; 
                     Eight; Nine; Ten; Jack; Queen; King]

let deck = [ for rank in ranks do
               for suit in suits do
                 yield Card(rank, suit) ]

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