Lex，Yacc和EBNF规范 [英] Lex and Yacc and EBNF specification

问题描述

如果我只想检查一种语言的语法是否正确， 使用yacc编写语法分析器的简单方法是什么?

if I just want to check whether the syntax of a language is correct or not, what is the easy way of writing a syntax analyzer using yacc.

推荐答案

请注意，用于EBNF的ISO标准是ISO 14977:1996，您在问题中使用的"EBNF"与标准版本具有有限的相似之处.这使我们不得不解释您的语法规则.

Note that the ISO standard for EBNF is ISO 14977:1996 and the 'EBNF' you've used in the question bears limited resemblance to the standard version. That leaves us having to interpret your grammar rule.

• 所有非小写字母都用单个单词写成非终结符.
• 端子以大写形式写成单个单词.
• 冒号用于将非终结符与其定义分开.
• 点(句点)用于标记规则的结束.
• 方括号包含可选的材料(零或一次).

牢记这些定义，您需要:

With those definitions in mind, you need:

• 将DECLARATION，OF，CONST，VAR，END识别为终端(关键字)的词法分析器.
• 一种语法，其中包含用于声明单位，标识，const_declaration，var_declaration，procedure_interface，function_interface的规则.

给出:

%token DECLARATION
%token OF
%token CONST
%token VAR
%token END

%%

declaration_unit
    :   DECLARATION OF ident opt_const_declaration opt_var_declaration
        opt_procedure_interface opt_function_interface DECLARATION END
    ;

opt_const_declaration
    :   /* Nothing */
    |   CONST const_declaration
    ;

opt_var_declaration
    :   /* Nothing */
    |   VAR var_declaration
    ;

opt_procedure_interface
    :   /* Nothing */
    |   procedure_interface
    ;

opt_function_interface
    :   /* Nothing */
    |   function_interface
    ;

您现在只需填写ident，const_declaration，var_declaration，procedure_interface，function_interface的规则.

You now just have to fill in the rules for ident, const_declaration, var_declaration, procedure_interface, function_interface.

对于简单的语法检查，您可以为尚未完全定义的语法部分添加占位符和规则.例如，您可以添加:

For simple syntax checking, you could add placeholder tokens and rules for the parts of the grammar that you've not yet fully defined. For example, you might add:

%token IDENT
%token CONST_DECLARATION
%token VAR_DECLARATION
%token PROCEDURE_INTERFACE
%token FUNCTION_INTERFACE

和

ident
    :   IDENT
    ;

const_declaration
    :   CONST_DECLARATION
    ;

var_declaration
    :   VAR_DECLARATION
    ;

procedure_interface
    :   PROCEDURE_INTERFACE
    ;

function_interface
    :   FUNCTION_INTERFACE
    ;

您的词法分析器只需要能够可靠地识别那些虚拟标记，直到您提供正确的规则即可.

Your lexical analyzer simply needs to be able to recognize those dummy tokens reliably until you provide the correct rules.

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