什么是函数式编程？

#Innolight

So. What is “functional programming,” exactly?
那么，究竟什么是“函数式编程”呢？

Functional programming isn’t a framework or a tool, but a way of writing code. In functional programming, we place a major emphasis on writing code using functions as “building blocks.”
函数式编程不是一种框架或工具，而是一种编写代码的方式。在函数式编程中，我们强调使用函数作为“构建块”来编写代码。

Your program is defined in terms of one main function. This main function is defined in terms of other functions, which are in turn defined in terms of still more functions — until at the bottom level the functions are just language primitives like “number” or “string.”
你的程序定义为一个主函数，这个主函数又由其他函数定义，而这些函数又进一步由更底层的函数定义，直到最底层，这些函数只是语言的基本元素，如“数字”或“字符串”。

Pasted image 20250402103922.png|650

If you’re reading this thinking, “Hmm, but wait? Doesn’t every language use functions to write code?” then good ?. It means you’re paying attention.
如果你正在阅读这篇文章，心想，“嗯？等等，难道不是每种语言都用函数来编写代码吗？”那么很好。这说明你在认真思考。

You’re right — every programming language has functions. But functional programming takes it to a whole ‘nother level ?
你说得对——每种编程语言都有函数。但函数式编程将其提升到了一个全新的层次？

Pasted image 20250402103949.png

To understand what I mean, let’s rewind and start with the basics.
为了理解我的意思，让我们回顾一下，从基础知识开始。

Every software program has two things:
每个软件程序都有两个东西：

  1. Behavior (what the program does) 行为（程序做什么）
  2. Data (data, is well, data) 数据（数据，很好，数据）

When we’re learning about a programming paradigm — like functional programming — it’s often helpful to consider how the paradigm approaches behavior and data respectively.
当我们学习一种编程范式——比如函数式编程——时，考虑该范式如何分别处理行为和数据通常很有帮助。

Behavior, in functional programming, is handled purely using functions in functional programming. Functions are “self contained” pieces of code that accomplish a specific task. They define a relationship between a set of possible inputs and a set of possible outputs — they usually take in data, process it, and return a result. Once a function is written, it can be used over and over and over again.
行为在函数式编程中完全通过函数来处理。函数是“自包含”的代码片段，用于完成特定任务。它们定义了一组可能的输入与一组可能的输出之间的关系——它们通常接收数据，处理它，并返回一个结果。一旦编写了一个函数，就可以反复使用它。

Data, in functional programming, is immutable — meaning it can’t be changed. Rather than changing data they take in, functions in functional programming take in data as input and produce new values as output. Always.
在函数式编程中，数据是不可变的——这意味着它不能被更改。与更改它们接收到的数据不同，函数式编程中的函数接收数据作为输入，并始终产生新的值作为输出。

Functions and immutable data are the only two things you need to ever deal with in functional programming. To make it even simpler, functions are treated no differently than data.
函数和不可变数据是你在函数式编程中需要处理的唯一两种事物。为了使其更加简单，函数被当作数据一样对待。

Put another way, functions in functional programming can be passed around as easily as data. You can refer to them from constants and variables, pass them as parameters to other functions, and return them as results from other functions.
换句话说，在函数式编程中，函数可以像数据一样轻松传递。你可以从常量和变量中引用它们，将它们作为参数传递给其他函数，也可以将它们作为其他函数的结果返回。

This is the most important thing to understand when approaching functional programming.
这是接近函数式编程时需要理解的最重要的事情。

Pasted image 20250402104142.png|650

By treating functions as nothing more special than a piece of data and by only using data that is immutable, we are given a lot more freedom in terms of how we can use functions.
通过将函数视为不比数据更特殊的东西，并且只使用不可变数据，我们在如何使用函数方面获得了更多的自由。

Namely, it allows us to create small, independent functions that can be reused and combined together to build up increasingly complex logic. We can break any complex problem down into smaller sub-problems, solve them using functions, and finally combine them together to solve the bigger problem.
也就是说，它允许我们创建小型、独立的函数，这些函数可以重复使用并组合在一起来构建越来越复杂的逻辑。我们可以将任何复杂问题分解成更小的子问题，使用函数来解决它们，最后将它们组合起来解决更大的问题。

Considering the ever-growing complexity of software applications, this kind of “building-block” approach makes a huge difference in keeping programs simple, modular, and understandable. This is also why developers strive to make their functions as general-purpose as possible, so that they can be combined to solve large, complex problems and reused to speed up development time for subsequent programs.
考虑到软件应用复杂性的不断增长，这种“积木式”的方法在保持程序简单、模块化和可理解性方面产生了巨大的影响。这也是为什么开发者们努力使他们的函数尽可能通用，以便它们可以组合起来解决大型、复杂的问题，并可以重复使用以加快后续程序的开发时间。

Pasted image 20250402104209.png|650

Ultimately, the reason that functions are so powerful in functional programming is because the functions follow certain core tenets.
最终，函数在函数式编程中之所以如此强大，是因为它们遵循某些核心原则。