Why Experts Exchange?

Experts Exchange always has the answer, or at the least points me in the correct direction! It is like having another employee that is extremely experienced.

Jim Murphy
Programmer at Smart IT Solutions

When asked, what has been your best career decision?

Deciding to stick with EE.

Mohamed Asif
Technical Department Head

Being involved with EE helped me to grow personally and professionally.

Carl Webster
CTP, Sr Infrastructure Consultant
Ask ANY Question

Connect with Certified Experts to gain insight and support on specific technology challenges including:

Troubleshooting
Research
Professional Opinions
Ask a Question
Did You Know?

We've partnered with two important charities to provide clean water and computer science education to those who need it most. READ MORE

troubleshooting Question

Writing a Compiler HELP~

Avatar of jtcy
jtcy asked on
Java
4 Comments1 Solution265 ViewsLast Modified:
Hi all, I am writing a compiler for a language called RCL, but stuck at the parser stage. Apparently, I have done the lexer, but now needs to do the parser. We are told to write a parser class, containing sub-parsers methods for each productions. And each sub parsers should also instantiate an AST node unique to that production. I am having problem of linking the lexer and the parser. i am stuck. here;s my lexer (its first part):

************************************************************************************
//First part of the descrition file: Contains codes to be added to the top of symbols.lex.java
import java.io.*;
import java.lang.System;
import compiler.sym;  // In here, all the definitions of token values
import ast.*;


class Compiler
  {
    /*
     * Just a simple driver - loops till end-of-file **
     * prints out the yytoken received..via the to_string method in yytoken
     *
     * **NOTE: Eof weirdness - For some strange reason (as yet unresolved)
     * it takes 3 (three) ^D's to make EOF happen.  Don't know why.
     *
     */
    static Yytoken current_symbol;
    static Yylex scanner;
   
    public static void main(String[] args) throws java.io.IOException
     {
            FileReader inFile = new FileReader(args[0]);
            scanner = new Yylex(inFile);
          
           do
            {
            
              System.out.println(current_symbol);
            }
            while (current_symbol.m_index != sym.EOF);
     }
     
     public Yytoken next_symbol() throws java.io.IOException
      {
          current_symbol = scanner.yylex();
          return current_symbol;
      }
      
      
      public boolean have(int s) throws java.io.IOException
      {
            if (current_symbol.m_index == s)
             {
                   next_symbol();
                   return (true);
             }
            else
                  return(false);
                  
      }

    public void mustbe(int s) throws java.io.IOException
    {
          if (current_symbol.m_index == s)
          {
                next_symbol();
          }
          else
          {
                System.out.println("error");
          }
    }
   
   
   
   
 }
 

 
class Utility
  {
    public static void my_assert(boolean expr)
      {
             if (false == expr)
               {
                  throw (new Error("Error: Assertion failed."));
               }
      }
    private static final String errorMsg[] =
     {
        "Error: Unmatched end-of-comment punctuation.",
        "Error: Unmatched start-of-comment punctuation.",
        "Error: Unclosed string.",
        "Error: Illegal character."
     };
    public static final int E_ENDCOMMENT = 0;
    public static final int E_STARTCOMMENT = 1;
    public static final int E_UNCLOSEDSTR = 2;
    public static final int E_UNMATCHED = 3;
    public static void error(int code)
      {
             System.out.println(errorMsg[code]);
      }
  }

class Yytoken
 {
   Yytoken (int index,String text,int line,int charBegin,int charEnd,String t_type)
      {
           m_index = index;
          m_text = new String(text);
          m_line = line;
          m_charBegin = charBegin;
          m_charEnd = charEnd;
          m_type = t_type;
      }
   public int m_index;
   public String m_text;
   public int m_line;
   public int m_charBegin;
   public int m_charEnd;
   public String m_type;
   public String toString()
    {
      return m_line +","+m_charBegin+":"+m_charEnd+"#"+m_type+"#"+m_text+"#";
    }
 }
 
******************************************************************************************

And here is my parser: i have only build an ifstatement production. just for testing.


import ast.*;
import compiler.sym;


public class Parser
{
   
   public Parser()
    {
          
    }

   
    public static ASTNode nIfStatement()
      {
            IfStatementNode thisOne = new IfStatementNode();
            mustbe(sym.tIF);
            thisOne.addchild(nRvalue());
            mustbe(sym.tTHEN);
            thisOne.addchild(nStatementList());
            while (have(sym.tELSEIF))
             {
                  thisOne.addchild(nRvalue());
                  mustbe(sym.tTHEN);
                  thisOne.addchild(nStatementList());
             };
            if (have(sym.tELSE))
             {
                   thisOne.addchild(nStatementList());
             }
            mustbe(sym.tENDIF);
            return thisOne;
      };
 
  }
  **************************************************************************************
 
 Okay, what i am not sure is where to put the mustbe() and have() method. I am confused on whether to implement like above, putting them in the lexer file or put in the parser file. Like now, the compiler would complain it cant find the mustbe method and have method.

Help~
 
 
 
 
 
 
 
 
 
 
 
ASKER CERTIFIED SOLUTION
Avatar of wll9111
wll9111

Our community of experts have been thoroughly vetted for their expertise and industry experience.

Commented:
This problem has been solved!
Unlock 1 Answer and 4 Comments.
See Answers