后面跟着一个等号（:: =）的双冒号在编程文档中是什么意思？

问题描述

例如在Lua文档中：

或Python文档：

解决方案

它表示，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 (::=).

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