Question

好的，所以我对Haskell非常陌生，而且我知道有很多关于这个东西的信息但是我不理解它。如果有人可以帮助解释并向我展示我做错的事情，那将非常感激，

这里有一些代码：

n = 8                     -- number of ingredients (excluding cream)

type Recipe = [Integer]   -- some ingredients

-- list all recipes with k of n ingredients

choose :: Integer -> Integer -> [Recipe]
choose n k
  | k == 0    = [[]]      -- only recipe with no ingredients

  | n == k    = [[1..n]]  -- only recipe with all ingredients

  | otherwise = choose (n-1) k ++ map (++ [n])(reverse (choose (n-1) (k-1)))

-- omlette legality (rules must hold conjunctively)

legal r = head $ map (\rule -> False) ruleset

ruleset = [rule0, rule1, rule2, rule3, rule4, rule5, rule6, rule7]


-- Rule 0: If truffles, then precisely truffles.
rule0 r = False

-- Rule 1: Either truffles, garlic, cream, or precisely one meat.
rule1 r = False 


-- Rule 2: Not both peppers and onions.
rule2 r = False

以下是成分

bacon     = elem 1
peppers   = elem 2
ham       = elem 3
mushrooms = elem 4
sausage   = elem 5
onions    = elem 6
garlic    = elem 7
truffles  = elem 8
cream     = elem 9

现在我试图改变规则，使它们满足注释要求，基本上搜索成分列表，

我尝试了一些东西

r = if any ( 5== ) Recipe

但很明显它没有用，有人可以详细说明我做错了吗

Answer 1

不要使用数字，而是使用您自己的数据类型，例如

data Ingredient = Bacon 
                | Peppers 
                | Ham 
                | Mushrooms 
                | Sausage
                | Onions 
                | Garlic
                | Truffles 
                | Cream 
                deriving (Eq, Ord, Bounded, Enum)

您可以使用enumFromTo

等功能获得一系列成分

然后你可以写像

这样的东西

rule2 receipt = not ((Peppers `elem` receipt) && (Onions `elem` receipt))

您可以使用

测试是否所有规则都适用

legal receipt = all ($ receipt)  ruleset

如何在Haskell中搜索整数列表

1 个答案: