JavaCC trace code...

[Brandi Love]

Hello!

I'm a new user to JavaCC and I could use some help if anyone is willing. So far I've written the .jj file for my code and have gotten JavaCC to generate all 7 files but now I want it to do something more and I'm not sure where to start. My parser uses a GUI. It takes the parser text in from an editable TextArea and appends the output to an uneditable TextArea. What I need my parser to do is to print out a message as it parses each token, something like this:
Expecting digit...
digit found at line 1, column 2.
The error reporting works perfectly correctly and I have the errors showing up in the TextArea for the output but how do I get JavaCC to output this kind of a message to my output TextArea? I'm not sure where to start. I've pasted the code for my .jj file below...

/**
 * JavaCC file
 */
 
options {
  JDK_VERSION = "1.5";
}
PARSER_BEGIN(BrandiParser)
import java.awt.*;
import java.awt.event.*;
import javax.swing.*;
import java.io.PipedInputStream;
import java.io.PipedOutputStream;
 
public class BrandiParser implements ActionListener {
private JFrame parserFrame;
private JPanel parserPanel;
private JLabel inputLabel;
private JLabel outputLabel;
private JLabel grammarLabel;
private TextArea inputTextArea;
private static TextArea outputTextArea;
private TextArea grammarTextArea;
private JScrollPane inputArea;
private JScrollPane outputArea;
private JScrollPane grammarArea;
private JButton parseButton;
private String input;
private static PipedInputStream pis;
private static PipedOutputStream pos;

public BrandiParser() { //GUI stuff
String grammar = "(Program::== Statement $\n" +
 "Statement::== P (Expr )\n" +
 "::== id = Expr \n" +
 "::== VarDecl \n" +
 "::== { StatementList }\n" + 
 "StatementList::== Statement StatementList\n" +
 "::== epsilon\n" +
 "Expr::== IntExpr\n" +
 "::== CharExpr\n" +
 "::== id\n" +
 "IntExpr::== digit op IntExpr\n" +
 "::== digit\n" +
 "CharExpr::== \" CharList \"\n" +
 "CharList::== Char CharList\n" +
 "::== epsilon \n" +
 "VarDecl::== Type Id\n" +
 "Type::== int | char\n" +
 "Id::== Char\n" +
 "Char::== a | b | c ... z\n" +
 "digit::== 1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 | 9 | 0\n" +
 "op::== + | -)";
parserFrame = new JFrame("A Simple Parser");
parserFrame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);

parserPanel = new JPanel(new GridBagLayout());
GridBagConstraints c = new GridBagConstraints();

grammarLabel = new JLabel("Grammar:", SwingConstants.LEFT);
inputLabel = new JLabel("Type your program here, then click the 'Parse' button: ", SwingConstants.LEFT);
outputLabel = new JLabel("Output: ", SwingConstants.LEFT);

grammarTextArea = new TextArea(grammar, 15, 55);
grammarTextArea.setEditable(false);
grammarArea = new JScrollPane(grammarTextArea);
grammarArea.setAutoscrolls(true);

inputTextArea = new TextArea (23, 55);
inputArea = new JScrollPane(inputTextArea);
inputArea.setAutoscrolls(true);

outputTextArea = new TextArea ("Your output will display here.", 44, 55);
outputTextArea.setEditable(false);
outputArea = new JScrollPane(outputTextArea);
outputArea.setAutoscrolls(true);

parseButton = new JButton ("Parse");

parseButton.addActionListener(this);

Color myBlue = new Color(238,247,255);
parserPanel.setBackground(myBlue);


c.gridx = 0;
c.gridy = 0;
parserPanel.add(grammarLabel, c);

c.gridx = 0;
c.gridy = 1;
parserPanel.add(grammarArea, c);

c.gridx = 0;
c.gridy = 2;
parserPanel.add(inputLabel, c);

c.gridx = 0;
c.gridy = 3;
parserPanel.add(inputArea, c);

c.gridx = 1;
c.gridy = 0;
parserPanel.add(outputLabel, c);

c.gridheight = 4;
c.gridx = 1;
c.gridy = 1;
parserPanel.add(outputArea, c);

c.gridheight = 0;
c.ipady = 15;
c.ipadx = 30;
c.gridx = 0;
c.gridy = 4;
parserPanel.add(parseButton, c);
 
parserFrame.getContentPane().add(parserPanel);
parserFrame.pack();
parserFrame.setVisible(true);
}

public void actionPerformed(ActionEvent arg0) { //Starts the parsing if 'parse' button is clicked
String inputString = inputTextArea.getText(); //Gets the input text
inputString = inputString + "$"; //Adds the end of file marker
try {
pos.write( inputString.getBytes() );
}
catch (Exception e) {
}
outputTextArea.setText(null);
}

private static void createAndShowGUI() { //GUI stuff
        JFrame.setDefaultLookAndFeelDecorated(true);
        BrandiParser parser = new BrandiParser();
    }
 
    public static void main(String[] args) {
    try {
pos = new PipedOutputStream();
        pis = new PipedInputStream(pos);
        System.setIn(pis);
}
catch (Exception e) {
}
        runGUI();
 
        BrandiParser parser = new BrandiParser(System.in);
    while (true) {
      try {
      switch (BrandiParser.program()) {
      case 0:
      outputTextArea.append("\nParsing complete.");
      break;
      case 1:
      outputTextArea.append("\nGoodbye.");
          break;
          default:
          break;
          }
      } catch (Exception e) {
      outputTextArea.append("\nERROR:  ");
        outputTextArea.append(e.getMessage());
        BrandiParser.ReInit(System.in);
      } catch (Error e) {
        outputTextArea.append("\nERROR:  ");
        outputTextArea.append(e.getMessage());
        break;
      }
    }
    }
    
    public static void runGUI () {
        javax.swing.SwingUtilities.invokeLater(new Runnable() {
            public void run() {
                createAndShowGUI();
            }
        });
    }
}
 
PARSER_END(BrandiParser)
 
SKIP :
{
 " " 
|"\r"
|"\t"
|"\n"
|"\r\n"
|"\\s"
}
TOKEN : /* EOF */
{ 
< END_OF_FILE: "$" >
}
TOKEN : /* DIGITS */
{ 
< DIGIT: ["0" - "9"] >
}
TOKEN : /*LETTERS*/
{ 
< CHAR : ["a"-"z"] > 
}
TOKEN: /*TYPE*/
{
< INT_TYPE: "int" >
|< CHAR_TYPE: "char" >
}
TOKEN : /* OPERATORS */
{ 
< PLUS: "+" >  
|< MINUS: "-" >
}
TOKEN : /* EQUALS */
{ 
< EQ: "=" >  
}
TOKEN : /* P */
{
< P: "P" >
}
TOKEN : /* OPEN PARENS */
{
< OPEN_PAR: "(" >
}
TOKEN : /* CLOSE PARENS */
{
< CLOSE_PAR: ")" >
}
TOKEN : /* OPEN CURLY BRACE */
{
< OPEN_BR: "{" >
}
TOKEN : /* CLOSE CURLY BRACE */
{
< CLOSE_BR: "}" >
}
TOKEN : /* QUOTE */
{
< QUOTE: " \" " >
}
TOKEN : /* EPSILON PRODUCTION */
{
< EP: "" >
}
 
int program() : {}
{
  statement() <END_OF_FILE> { return 0; }
|<END_OF_FILE> { return 1; }
}
void statement() : {}
{
<P> <OPEN_PAR> expr() <CLOSE_PAR>
|id() <EQ> expr()
|varDecl()
|<OPEN_BR> statementList() <CLOSE_BR>
}
void statementList() : {}
{
  statement() statementList() 
//|<EP>
}
void expr() : {}
{
intExpr()
| charExpr()
|id()
}
void intExpr() : {}
{
LOOKAHEAD(2)
<DIGIT> op() intExpr()
|<DIGIT>
}
void charExpr() : {}
{
<QUOTE> charList() <QUOTE>
}
void charList() : {}
{
<CHAR> charList() 
//|<EP>
}
void varDecl() : {}
{
(<INT_TYPE> | <CHAR_TYPE> :wink:  id()
}
void id() : {}
{
<CHAR>
}
void op() : {}
{
<PLUS> | <MINUS>
}

[Campbell Ritchie]

Not familiar with the tool. There ought to be documentation telling you what you are returning.

Put another line in your catch(Error e) block like this:-

if (e instanceof ThreadDeath) throw e;

as required here.

I have used other lexical scanners, which produce some sort of return value. You ought to have a method to add something like this:-

public Symbol getSymbol(int code, Object value)
{
   return new Symbol(code, value);
}
 
public Symbol getSymbol(int code)
{
   return getSymbol(code, null);
}

. . . and you need to put a line in with each TOKEN: definition on the lines of "return getSymbol(INT_TYPE, Integer.parseInt(yytext()));"

As I said, there ought to be documentation with the tool on its website telling you what you are supposed to do, and there will probably be worked examples for you to study.

BTW: A digit or a character DOES NOT constitute a token.

[Brandi Love]

I overlooked a very simple solution to this one - all you need to do if you want a trace is to set DEBUG_PARSER = true under options in the .jj file.