如何在Haskell中搜索整数列表

Question

好的，所以我对Haskell来说是个新手，我知道这方面有很多信息，但我只是不了解。 如果有人可以帮助解释并告诉我我在做错什么，将不胜感激，

这是一些代码：

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 

这是成分

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，我正在尝试更改规则，以使其符合注释掉的要求，本质上是在成分列表中进行搜索，我尝试了一些类似的方法

r = if any ( 5== ) Recipe

但是很明显它没有用，有人可以详细说明我在做什么

Answer 1

不要使用数字，而要使用自己的数据类型，例如

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

您可以通过使用诸如enumFromTo函数来获得各种配料

然后你可以写一些东西

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

您可以使用以下方法测试所有规则是否都适用

legal receipt = all ($ receipt)  ruleset