I am a beginner of antlr. I was trying to use visitor in my code and following the instruction on the net. However, I found out that the visitor was not entering the method I create at all. May anyone tell me what I did wrong?
This is my visitor:
import java.util.LinkedList;
import org.antlr.v4.runtime.misc.NotNull;
/*
* To change this template, choose Tools | Templates
* and open the template in the editor.
*/
/**
*
* @author Sherwood
*/
public class ExtractMicroBaseVisitor extends MicroBaseVisitor<Integer> {
//LinkedList<IR> ll = new LinkedList<IR>();
//MicroParser parser;
//System.out.println("11");
@Override
public Integer visitPgm_body(@NotNull MicroParser.Pgm_bodyContext ctx){
System.out.println(ctx.getText());
return 467;
}
@Override
public Integer visitProgram(@NotNull MicroParser.ProgramContext ctx){
System.out.println("11");
return 456;
}
}
As you can see, the stdout should print 11 when the method "visitProgram" was entered. But the output screen gave me nothing (a null type).
This is my main code:
import java.io.IOException;
import org.antlr.v4.runtime.*;
import org.antlr.v4.runtime.tree.*;
/**
*
* @author Sherwood
*/
public class Compiler {
/**
* @param args the command line arguments
*/
public static void main(String[] args) {
// TODO code application logic here
//SymbolTable table = new SymbolTable();
try {
ANTLRFileStream reader = new ANTLRFileStream("TestCases/step4_testcase3.micro");
MicroLexer lexer = new MicroLexer((CharStream)reader);
TokenStream tokens = new CommonTokenStream(lexer);
MicroParser parser = new MicroParser(tokens);
parser.setErrorHandler(new MyErrorStrategy());
ParseTree tree = parser.program();
//ParseTreeWalker walker = new ParseTreeWalker(); // create standard walker
//ExtractMicroBaseListener extractor = new ExtractMicroBaseListener(parser);
//walker.walk(extractor, tree); // initiate walk of tree with listener
ExtractMicroBaseVisitor visitor = new ExtractMicroBaseVisitor();
int t = visitor.visit(tree);
//for(String str : extractor.table.checkDuplicate()){
// System.out.println("SHADOW WARNING " + str);
//}
//System.out.println(extractor.table.checkDuplicate().toString());
//System.out.println(extractor.table.toString());
//System.out.println("Accepted");
}catch (IOException e) {
System.out.println("Not Accepted");
}catch(IllegalArgumentException e){
System.out.println(e.getMessage());
}
}
}
This is my grammar file(partially):
grammar Micro;
options {
language = Java;
}
//Program
program : ('PROGRAM' id 'BEGIN' pgm_body 'END')
;
id : IDENTIFIER;
pgm_body : (decl func_declarations);
decl : (string_decl_list | var_decl_list)* ;
You have to call super
if you want ANTLR4 to visit children. Like this:
@Override
public Integer visitPgm_body(@NotNull MicroParser.Pgm_bodyContext ctx){
super.visitPgm_body(ctx);
System.out.println(ctx.getText());
return 467;
}
@Override
public Integer visitProgram(@NotNull MicroParser.ProgramContext ctx){
super.visitProgram(ctx);
System.out.println("11");
return 456;
}
You have to think about where to put your logic: before super
or after.