在 Haskell 中访问自定义数据类型的成员 [英] Accessing members of a custom data type in Haskell

问题描述

假设我在 Haskell 中有以下自定义数据类型和函数:

Say I have the following custom data type and function in Haskell:

data Person = Person { first_name :: String, 
                       last_name :: String,
                       age :: Int 
                     } deriving (Eq, Ord, Show)

如果我想创建一个函数 print_age 来打印一个人的年龄，像这样: print_age (Person "John" "Smith" 21) ，我该怎么写print_age 访问年龄参数?我是一个面向对象的人，所以我在这里不合时宜.我基本上是在寻找相当于 Person.age 的东西.

If I want to create a function print_age to print a Person's age, like so: print_age (Person "John" "Smith" 21) , how would I write print_age to access the age parameter? I'm an Object Oriented guy, so I'm out of my element here. I'm basically looking for the equivalent of Person.age.

推荐答案

Function application 是前缀，所以 age person 将对应于常见的 person.age()面向对象语言.print_age 函数可以通过函数组合来定义pointfree

Function application is prefix, so age person would correspond to the person.age() common in OOP languages. The print_age function could be defined pointfree by function composition

print_age = print . age

或点满

print_age person = print (age person)

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