Question

newtype Name = Name String deriving (Show)
newtype Age = Age Int deriving (Show)
newtype Weight = Weight Int deriving (Show)
newtype Person = Person (Name, Age, Weight) deriving (Show)   
type Gym = [Person]

isAdult :: Person -> Bool
isAdult (Person (_, Age a, _)) = a > 18

w = Person (Name "Lee", Age 30, Weight 120)

p = Person (Name "John" , Age 65, Weight 80)

updateWeight :: Person -> Int -> Person
updateWeight (Person (n, a, Weight w)) b = Person (n,  a, Weight $ w + b)

getWeight :: Person -> Int
getWeight (Person (a, b, Weight c)) = c

getAge :: Person -> Int
getAge (Person (a, Age b, c)) = b

我现在正想着尝试在两个年龄段内找到健身房里人的平均体重。

到目前为止我已经

了

getAverage:: Gym -> (Int, Int) -> Int
getAverage a (b,c) = sum . map getWeight . filter ((b >= age && c <= age) || (b <= age && c >= age))
    where
        age = getAge a

Answer 1

你所拥有的是近在咫尺，但并不完全在那里。我建议将问题分解为子表达式，并使用where或let本地绑定来更清楚地说明您要执行的操作：

getAverage :: Gym -> (Int, Int) -> Double
getAverage gym (minAge, maxAge) = fromIntegral total / fromIntegral count
    where
        isInAgeRange person = minAge <= age && age <= maxAge where age = getAge person
        validPeople = filter isInAgeRange gym
        total = sum $ map getWeight validPeople
        count = length validPeople

从这一点开始，您可以将这些行中的一些组合起来以缩短代码，但这非常易读，它不会受到许多效率问题的困扰（尽管您可以同时计算总和和计数）一个花哨的折叠，并没有太多的线来写，因为它。

基本的haskell：找到两个值之间的平均值

1 个答案: