BNF 中的 JavaScript for 循环

发布于 2024-07-18 07:09:27 字数 493 浏览 5 评论 0原文

我正在为 JavaScript 编写 BNF，它将用于生成该语言的词法分析器和解析器。不过，我想要一些关于如何设计 for 循环的想法。这是我当前 BNF 的简化版本：

[...]
VarDecl. Statement ::= "var" Identifier "=" Expr ";"
ForLoop. Statement ::= "for" "(" Expr ";" Expr ";" Expr ")"
[...]

如您所见，示例中有两个语句，变量声明和 for 循环。有很多不同的表达式，但没有一个表达式也是语句。

现在的问题是这段 JavaScript 代码不会通过解析器：

for (var x = 3; [...]; [...])

这是因为变量声明不是表达式。

您对如何解决这个问题有什么想法？我可以想到几个办法，但是不想妨碍大家自己的想法，所以这里就不说了。

原文

I'm writing BNF for JavaScript which will be used to generate a lexer and a parser for the language. However, I'd like some ideas on how to design the for-loop. Here is the simplified version of my current BNF:

[...]
VarDecl. Statement ::= "var" Identifier "=" Expr ";"
ForLoop. Statement ::= "for" "(" Expr ";" Expr ";" Expr ")"
[...]

So as you can see, there are two statements in the example, variable declarations and for-loops. There are a bunch of different expressions, but none of the expressions are also statements.

The problem now is that this JavaScript code will not pass through the parser:

for (var x = 3; [...]; [...])

This is because a variable declaration is not an expression.

What are your ideas on how to solve this? I can think of a few ways, but I don't want to get in the way of your own thoughts, so I won't mention them here.

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你的呼吸 2024-07-25 07:09:27

网上有一些示例，在 ANTLR ECMAScript 语法中，您可以找到这个结构：

iterationStatement:
'do' statement 'while' LPAREN expression RPAREN SEMI
| 'while' LPAREN expression RPAREN statement
| 'for' LPAREN (
    (expressionNoln)? SEMI (expression)? SEMI (expression)? RPAREN statement
    | 'var' variableDeclarationListNoln SEMI (expression)? SEMI (expression)? RPAREN statement
    | leftHandSideExpression 'in' expression RPAREN statement   
    | 'var' variableDeclarationNoln 'in' expression RPAREN statement
    )
;

There are a few examples over the net, in an ANTLR ECMAScript grammar you can find this structure:

iterationStatement:
'do' statement 'while' LPAREN expression RPAREN SEMI
| 'while' LPAREN expression RPAREN statement
| 'for' LPAREN (
    (expressionNoln)? SEMI (expression)? SEMI (expression)? RPAREN statement
    | 'var' variableDeclarationListNoln SEMI (expression)? SEMI (expression)? RPAREN statement
    | leftHandSideExpression 'in' expression RPAREN statement   
    | 'var' variableDeclarationNoln 'in' expression RPAREN statement
    )
;

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