后面跟着一个等号（:: =）的双冒号在编程文档中是什么意思？ [英] What does a double colon followed by an equals sign (::=) mean in programming documentation?

问题描述

例如在Lua文档中： href =http://www.lua.org/manual/5.2/manual.html#3.2 =noreferrer> http://www.lua.org/manual/5.2/manual.html#3.2

或Python文档： http://docs.python.org/release/2.7.1/reference/lexical_analysis.html#identifiers

解决方案

它表示 Backus-Naur表单

含义：

 < symbol> :: = __expression__ 
  

nonterminal < symbol> 由...组成（被定义为，由...构造，从...导出） __表达式__

它用于描述语言语法。

请注意，这两个示例都在扩展Backus -Naur表单，但使用传统的BNF符号表达式分隔符（ :: = ）。

What does ::= mean in programming documentation?

For example in the Lua documentation: http://www.lua.org/manual/5.2/manual.html#3.2

Or the Python documentation: http://docs.python.org/release/2.7.1/reference/lexical_analysis.html#identifiers

解决方案

It symbolizes 'symbol derivation rule' in Backus–Naur Form

Meaning that in:

<symbol> ::= __expression__ 

nonterminal <symbol> consists of (is defined as, is constructed from, derives from) __expression__

It's used to describe language grammars.

Notice that both examples are in Extended Backus–Naur Form, but using a traditional BNF symbol-expression separator (::=).

这篇关于后面跟着一个等号（:: =）的双冒号在编程文档中是什么意思？的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！