在Antlr中定义语法 [英] define a grammar in Antlr

问题描述

我定义了以下语法.

grammar Sample_1;


@header {
  package a;
}

@lexer::header {
  package a;
}

program
    :   
        define*
        implement*
    ;


define
    :   IDENT '=(' INTEGER',' INTEGER ')'
    ;

implement
    :IDENT '=(' (IDENT ','?)* ')'
    ;

fragment LETTER : ('a'..'z' | 'A'..'Z') ;
fragment DIGIT : '0'..'9';
INTEGER : DIGIT+ ;
IDENT : LETTER (LETTER | DIGIT)*;
WS : (' ' | '\t' | '\n' | '\r' | '\f')+ {$channel = HIDDEN;};
COMMENT : '//' .* ('\n'|'\r') {$channel = HIDDEN;};

如何检查语法，以便在我有示例时

How to check in this grammar so that when I have the example

A=(1,1)
B=(1,2)

G=(A,B)

结果成功，但是如果我写

the result is successful but if I write

A=(1,1)
B=(1,2)

G=(A,E)

它给出一个错误，未定义E 谢谢

it gives an error that E is not defined thanks

结果: 我让它正常工作非常感谢:

the result: i got it working thanks a lot:

grammar Sample_1;

@members{
    int level=0;
}

@header {
  package a;
}

@lexer::header {
  package a;
}

program
    :   
        block
    ;
block   
scope {
    List symbols;
}
@init {
    $block::symbols=new ArrayList();
    level++;
}
@after { 
     System.err.println("Hello");
     level--;
 }
    : (define* implement+)
    ;

define
    :   IDENT {$block::symbols.add($IDENT.text);} '=(' INTEGER',' INTEGER ')' 
    ;

implement
    :IDENT '=(' (a=IDENT 
    {if (!$block::symbols.contains($a.text)){
    System.err.println("undefined");
    }}','?)* ')'
    ;

fragment LETTER : ('a'..'z' | 'A'..'Z') ;
fragment DIGIT : '0'..'9';
INTEGER : DIGIT+ ;
IDENT : LETTER (LETTER | DIGIT)*;
WS : (' ' | '\t' | '\n' | '\r' | '\f')+ {$channel = HIDDEN;};
COMMENT : '//' .* ('\n'|'\r') {$channel = HIDDEN;};

推荐答案

Antlr支持 actions ，这是语法文件中嵌入的少量代码段.

Antlr supports actions, little snippets of code embedded in the grammar file.

一项分配动作可以存储到地图中.右侧IDENT的操作可能会尝试从映射中提取一个值，如果失败则抛出异常.

An action for an assignment could store into a map. An action for a right-hand-side IDENT could try to pull a value from the map, and throw an exception if it fails.

Terrence Parr的权威ANTLR参考"的第6章介绍了动作.

Chapter 6 in Terrence Parr's "The Definitive ANTLR Reference" covers actions.

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