javascript - 此语法是否通过右递归定义右结合性

Question

我正在阅读 this article关于将 ** 运算符添加到 EcmaScript 规范中，作者声明如下:

Exponentiation must be evaluated before multiplication and more importantly, the BNF grammar must be written such that the operator’s right-associativity is clearly defined (unlike MultiplicativeExpression, which is left-associative).

并且他在文法中定义了新的非终结符号ExponentiationExpression为:

ExponentiationExpression : 
  UnaryExpression[?Yield]
  UnaryExpression[?Yield] ** ExponentiationExpression[?Yield]

MultiplicativeExpression[Yield] :
  ExponentiationExpression[?Yield]
  MultiplicativeExpression[?Yield] MultiplicativeOperator ExponentiationExpression[?Yield]

This article指出:

To write a grammar that correctly expresses operator associativity:

• For left associativity, use left recursion.
• For right associativity, use right recursion.

他似乎遵循了该规则并通过对此处的 ExponentiationExpression 使用右递归 来定义结合律:

ExponentiationExpression -> UnaryExpression[?Yield] ** ExponentiationExpression[?Yield]

我说得对吗？

Answer 1

Am I right?

是。