First-class function 头等函数

Python 介绍说 Python has first class functions，记得lua也这么说过，那么头等函数是什么意思是呢？

摘自first class functions wiki百科

In computer science, a programming language is said to have first-class functions if it treats functions as first-class citizens. Specifically, this means the language supports passing functions as arguments to other functions, returning them as the values from other functions, and assigning them to variables or storing them in data structures.

在计算机科学中，如果一门编程语言把函数看做头等公民就可以这门语言支持头等函数。具体也就是说，函数能像参数那样被传递到另一个函数、从另一个函数那像值一样被返回出来、函数可以赋值给变量或者存在数据结构中。

头等公民

摘自first-class citizens wiki百科

In programming language design, a first-class citizen (also object, entity, or value) in a given programming language is an entity which supports all the operations generally available to other entities. These operations typically include being passed as a parameter, returned from a function, and assigned to a variable.