ANTLR是否可以在内部嵌入语法制作语法?

本文介绍了ANTLR是否可以在内部嵌入语法制作语法?的处理方法，对大家解决问题具有一定的参考价值，需要的朋友们下面随着小编来一起学习吧！ 问题描述

ANTLR:是否可以通过在内部嵌入语法(使用自己的词法分析器)来制作语法?

ANTLR: Is it possible to make grammar with embed grammar (with it's own lexer) inside?

例如，以我的语言，我可以使用嵌入式SQL语言:

For example in my language I have ability to use embed SQL language:

var Query = [select * from table]; with Query do something ....;

使用ANTLR可以吗?

Is it possible with ANTLR?

推荐答案

是否可以通过在内部嵌入语法(带有自己的词法分析器)来制作语法?

Is it possible to make grammar with embed grammar (with it's own lexer) inside?

如果您的意思是是否可以在一个语法中定义两种语言(使用单独的词法分析器)，那么答案是:不，那是不可能的.

If you mean whether it is possible to define two languages in a single grammar (using separate lexers), then the answer is: no, that's not possible.

但是，如果问题是是否可以将两种语言解析为一个AST，那么答案是:是的，这是可能的.

However, if the question is whether it is possible to parse two languages into a single AST, then the answer is: yes, it is possible.

您只需要:

• 用自己的语法定义两种语言；
• 在您的主语法中创建一个词法分析器规则，以捕获嵌入式语言的全部输入；
• 使用重写规则，该规则调用一个自定义方法，该方法将解析外部AST并使用{ ... }将其插入到主AST中(请参阅主语法(MyLanguage.g)中的expr规则).

• define both languages in their own grammar;
• create a lexer rule in you main grammar that captures the entire input of the embedded language;
• use a rewrite rule that calls a custom method that parses the external AST and inserts it in the main AST using { ... } (see the expr rule in the main grammar (MyLanguage.g)).

grammar MyLanguage; options { output=AST; ASTLabelType=CommonTree; } tokens { ROOT; } @members { private CommonTree parseSQL(String sqlSrc) { try { MiniSQLLexer lexer = new MiniSQLLexer(new ANTLRStringStream(sqlSrc)); MiniSQLParser parser = new MiniSQLParser(new CommonTokenStream(lexer)); return (CommonTree)parser.parse().getTree(); } catch(Exception e) { return new CommonTree(new CommonToken(-1, e.getMessage())); } } } parse : assignment+ EOF -> ^(ROOT assignment+) ; assignment : Var Id '=' expr ';' -> ^('=' Id expr) ; expr : Num | SQL -> {parseSQL($SQL.text)} ; Var : 'var'; Id : ('a'..'z' | 'A'..'Z')+; Num : '0'..'9'+; SQL : '[' ~']'* ']'; Space : ' ' {skip();};

MiniSQL.g

grammar MiniSQL; options { output=AST; ASTLabelType=CommonTree; } parse : '[' statement ']' EOF -> statement ; statement : select ; select : Select '*' From ID -> ^(Select '*' From ID) ; Select : 'select'; From : 'from'; ID : ('a'..'z' | 'A'..'Z')+; Space : ' ' {skip();};

Main.java

import org.antlr.runtime.*; import org.antlr.runtime.tree.*; import org.antlr.stringtemplate.*; public class Main { public static void main(String[] args) throws Exception { String src = "var Query = [select * from table]; var x = 42;"; MyLanguageLexer lexer = new MyLanguageLexer(new ANTLRStringStream(src)); MyLanguageParser parser = new MyLanguageParser(new CommonTokenStream(lexer)); CommonTree tree = (CommonTree)parser.parse().getTree(); DOTTreeGenerator gen = new DOTTreeGenerator(); StringTemplate st = gen.toDOT(tree); System.out.println(st); } }

运行演示

java -cp antlr-3.3.jar org.antlr.Tool MiniSQL.g java -cp antlr-3.3.jar org.antlr.Tool MyLanguage.g javac -cp antlr-3.3.jar *.java java -cp .:antlr-3.3.jar Main

输入:

var Query = [select * from table]; var x = 42;

Main类的输出对应于以下AST:

the output of the Main class corresponds to the following AST:

如果您想在SQL中允许使用字符串文字(可能包含])和注释(可能包含'和])，则可以在您的SQL中使用以下SQL规则主要语法:

And if you want to allow string literals inside your SQL (which could contain ]), and comments (which could contain ' and ]), the you could use the following SQL rule inside your main grammar:

SQL : '[' ( ~(']' | '\'' | '-') | '-' ~'-' | COMMENT | STR )* ']' ; fragment STR : '\'' (~('\'' | '\r' | '\n') | '\'\'')+ '\'' | '\'\'' ; fragment COMMENT : '--' ~('\r' | '\n')* ;

可以在单个令牌中正确解析以下输入:

which would properly parse the following input in a single token:

[ select a,b,c from table where a='A''B]C' and b='' -- some ] comment ] here' ]

请注意，尝试为整个SQL方言(甚至是很大的子集)创建语法并不是一件容易的事！您可能要搜索现有的SQL解析器，或查看ANTLR Wiki中的示例语法.

Just beware that trying to create a grammar for an entire SQL dialect (or even a large subset) is no trivial task! You may want to search for existing SQL parsers, or look at the ANTLR wiki for example-grammars.