榆树初学者:试图写二十一点

Question

我正在做一个关于榆树的独立研究,我觉得我正在学习重新编程!作为一个学习语言的项目,我试图让一个简单的二十一点启动和运行,但一旦我开始,我意识到我仍然没有掌握多少.我从甲板上绘制卡片并将它们添加到列表中:

import Random
import Mouse
import Array

--Build the deck
faces = [1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13]
suits = ['H', 'D', 'C', 'S']

allCards faces suits =
  case suits of
    x :: xs -> family faces x ++ allCards faces xs
    _ -> []

family faces suit =
  case faces of
    x :: xs -> (,) x suit :: family xs suit
    _ -> []

deck = allCards faces suits

rand : Signal Int
rand = Random.range 0 (length deck-1) Mouse.clicks 

pickCard n = head <| drop n deck
nextCard = lift pickCard rand

yourHand = foldp (::) [] nextCard

main = lift asText yourHand

我的问题主要是关于如何继续.看完已完成的榆树项目有点帮助,但其中很多都很难让我作为初学者进行解析.任何方向都有帮助!

1. 我遇到的第一个问题之一是试图弄清楚如何从牌组中取出牌,使用类似的dropCard deck card = filter (\card /= nextCard) deck方法从列表中过滤出抽出的牌.但我对榆树的理解是,每当信号发生变化时,程序就会重新评估,这意味着每次抽取卡片时都会重新创建一副牌.我还需要foldp原始套牌吗？

2. 从一个列表中删除元素并在函数式编程中将其添加到另一个列表的正确方法是什么？功能构成,喜欢toHand . dropCard card？

3. 为了添加卡面以确定输赢,我不确定如何从列表中获取整数值.我试过了fst (head deck),但是我遇到了类型错误,可能是因为deck本身就是某种信号.有什么我没看到的吗？

那就是说,到目前为止我真的很享受榆树!

Answer 1

问题

1. 对于简单程序,最简单的思考信号的方法是考虑程序中的哪些类型可以改变.在你的情况下,这将是甲板和手.然后你拿走这些东西并建立一个数据结构来存储它们.然后你foldp在整个数据结构上进行操作,所以不仅要跟踪手,还要跟踪平台.
2. 您可以编写一个获取列表和索引的函数,并返回列表中该索引处的项目以及删除该项目的列表.然后将项目添加到另一个列表中,您就完成了.
3. fst (head deck)应该管用.也许你lift在main尝试时忘了在定义中删除它？

示例代码

-- This first part is your code:
import Random
import Mouse
import Array

--Build the deck
faces = [1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13]
suits = ['H', 'D', 'C', 'S']

allCards faces suits =
  case suits of
    x :: xs -> family faces x ++ allCards faces xs
    _ -> []

family faces suit =
  case faces of
    x :: xs -> (,) x suit :: family xs suit
    _ -> []

-- Here come my additions/changes:
-- Naming some types for clarity
type Card = (Int,Char)
type ProgramState = { deck : [Card], hand : [Card] }

getFromList : Int -> [a] -> (a,[a])
getFromList index list =
  let prefix = take index list
      (item :: postfix) = drop index list
  in (item, prefix ++ postfix)

startState : ProgramState
startState = { deck = allCards faces suits, hand = [] }

rand : Signal Float
rand = Random.float Mouse.clicks 

rFloatToInt : Float -> Int -> Int -> Int
rFloatToInt rnd lo hi = round ((rnd + toFloat lo) * toFloat hi)

pickCard : Float -> ProgramState -> ProgramState
pickCard rnd {deck,hand} = 
  let index = rFloatToInt rnd 0 (length deck - 1)
      (item, newDeck) = getFromList index deck
  in { deck = newDeck, hand = item :: hand }

programState : Signal ProgramState
programState = foldp pickCard startState rand

main : Signal Element
main = lift asText programState

如果有什么不清楚,请告诉我.