Adding an Antlr4 parse tree to another Antlr4 parse tree

Question

I need to implement generics with Antlr4. In order to do this, I need to be able to take a class and, as it is used, dynamically generate code for it like a macro, tokenize that code, generate a tree, and then add that new tree to my original parse tree.

I saw these two classes

http://www.antlr.org/api/JavaTool/org/antlr/v4/runtime/RuleContext.html

http://www.antlr.org/api/JavaTool/org/antlr/v4/runtime/ParserRuleContext.html

However, I'm not sure what they actually do, nor am I sure how to use the constructor.

ParserRuleContext(ParserRuleContext parent, int invokingStateNumber)

RuleContext(RuleContext parent, int invokingState)

Specifically, are these the classes that will represent the new tree, and what should I pass into invokingState/invokingStateNumber?

Generally, Antlr4 does not support direct modification of the parse tree. Might be better to back up a step and ask the question of where and how generics can be implemented given more specifics about what you are trying to do. — GRosenberg
Sadly, there is no way to implement generics except by this method. Guess I'll dive into the constructor and try to figure out what that int argument does >: o. — nestharus

nestharus nestharus · Accepted Answer · 2015-04-15T04:41:46

Apparently it is as easy as this

When walking the first tree, it correctly displays information from both files.

    public class Program
    {
            private static ParserRuleContext getTree(String file) throws Exception
            {
                    InputStream input = new FileInputStream(file);
                    Reader reader = new InputStreamReader(input);
                    ANTLRInputStream inputStream = new ANTLRInputStream(reader);

                    JavaLexer lexer = new JavaLexer(inputStream);
                    CommonTokenStream tokens = new CommonTokenStream(lexer);
                    JavaParser parser = new JavaParser(tokens);
                    ParserRuleContext tree = parser.compilationUnit(); // parse

                    return tree;
            }

            public static void main(String args[]) throws Exception
            {
                    ParserRuleContext tree1 = getTree("E:\\Users\\nessy\\IdeaProjects\\AntlrTest\\src\\in1.java");
                    ParserRuleContext tree2 = getTree("E:\\Users\\nessy\\IdeaProjects\\AntlrTest\\src\\in2.java");

                    tree1.addChild(tree2);

                    ParseTreeWalker walker = new ParseTreeWalker(); // create standard walker
                    JavaWalker extractor = new JavaWalker();
                    walker.walk(extractor, tree1); // initiate walk of tree with listener
            }
    }

Adding an Antlr4 parse tree to another Antlr4 parse tree

1 Answers