ANTLR4：如何在可能用于查找起始规则的语法中查找根规则

Question

我一直在查看位于：

的语法

Antlr 4 grammars

我一直在使用 Antlrworks 2 查看它们，但是我发现很难找到整个语法的起始规则。

我认为开始规则的定义是一个没有其他指针指向它的节点，有没有人有找到这些语法的开始规则的有效解决方案？

Answer 1

为了找到 root/start 规则，我实现了一个 ANTLR 树监听器，它创建了一个 ANTLR 语法中所有规则的邻接列表，并检查是否没有其他语法规则引用它。这将提示开始规则可能是什么。

为了运行，你将需要取自Antlr 4 grammar

的antlr语法

监听器实现如下：

(RootFinder.java)

import java.util.ArrayList;
import java.util.Collection;
import java.util.HashSet;
import java.util.LinkedHashMap;
import java.util.List;
import java.util.Map;
import java.util.Map.Entry;
import java.util.Set;


public class RootFinder extends ANTLRv4ParserBaseListener {

    private Set<String> rules = new HashSet<String>( );
    public Map<String, Set<String>> adjacencyList = new LinkedHashMap<String, Set<String>>( );

    public void enterParserRuleSpec(ANTLRv4Parser.ParserRuleSpecContext ctx)
    {
        rules = new HashSet<String>( );     
    }

    public void exitParserRuleSpec(ANTLRv4Parser.ParserRuleSpecContext ctx)
    {
        if(ctx != null)
        {
            adjacencyList.put(ctx.RULE_REF().getText(), rules);
        }
    }

    public void exitRuleref(ANTLRv4Parser.RulerefContext ctx) {
        if(ctx != null)
        {
            rules.add(ctx.getText());
        }
    }

    public List<String> leafNodes( )
    {
        List<String> leafs = new ArrayList<String>( );
        for(Entry<String, Set<String>> entry : adjacencyList.entrySet())
        {
            if( entry.getValue().size() == 0)
            {
                leafs.add(entry.getKey());
            }
        }
        return leafs;
    }

    public Set<String> rootNodes( )
    {
        Set<String> roots = new HashSet<String>( );
        Collection<Set<String>> values = adjacencyList.values();

        for(Entry<String, Set<String>> entry : adjacencyList.entrySet())
        {
            boolean found = false;
            for(Set<String> vals : values)
            {
                if(vals.contains(entry.getKey()))
                {
                    found = true;
                }
            }
            if(found == false)
            {
                roots.add(entry.getKey());
            }
        }
        return roots;
    }
}

这是运行的主程序

(Main.java)

import java.io.IOException;

import org.antlr.v4.runtime.ANTLRFileStream;
import org.antlr.v4.runtime.ANTLRInputStream;
import org.antlr.v4.runtime.CommonTokenStream;
import org.antlr.v4.runtime.tree.ParseTree;


public class Main {

    public static void main(String[] args) throws IOException {

        String filename = args[0];
        ANTLRInputStream reader = new ANTLRFileStream(filename);
        ANTLRv4Lexer lexer = new ANTLRv4Lexer(reader);
        CommonTokenStream tokenStream = new CommonTokenStream(lexer);
        ANTLRv4Parser parser = new ANTLRv4Parser(tokenStream);
        RootFinder rootfinder = new RootFinder();
        parser.addParseListener(rootfinder);

        ParseTree tree = parser.grammarSpec();
        System.out.println(rootfinder.leafNodes());
        System.out.println(rootfinder.rootNodes());
    }

}

ANTLR4：如何在可能用于查找起始规则的语法中查找根规则

ANTLR4: How to find the root rules in a gramar which maybe used to find the start rule

antlr4

antlrworks2