Subversion Repositories programming

/*******************************************************************************

 * File: robot.y

 * 

 * Copyright (c) 2006, Ira W. Snyder (devel@irasnyder.com)

 * License: GNU General Public License v2

 *

 * This file implements the grammar that controls our fictional apple-bag

 * robot from Project #3, Question #2.

 ******************************************************************************/

%{

    import java.lang.*;

    import java.io.*;

    import java.util.StringTokenizer;

%}

/* Token Declarations */

%token PUT

%token TAKE

/* Robot Grammar */

%%

program : S         { System.out.println ("There are: " + r.getVal() + " apples in the bag!"); };

S : PUT S TAKE S    { System.out.println ("S -> PUT S TAKE S"); }

    | PUT S         { System.out.println ("S -> PUT S"); r.incVal(); }

    |               { System.out.println ("S -> epsilon"); };

%%

private Yylex lexer;

public void yyerror (String error)

{

    System.out.println ("Parse Error: " + error);

}

int yylex ()

{

    int lex_return = -1;

    try

    {

        lex_return = lexer.yylex();

    }

    catch (IOException e)

    {

        System.out.println ("IO Error: " + e);

    }

    return lex_return;

}

public Parser (Reader r)

{

    lexer = new Yylex (r, this);

}

public static void main (String[] args) throws Exception

{

    try

    {

        Parser yyparser = new Parser (new FileReader (args[0]));

        yyparser.yyparse();

    }

    catch (Exception e)

    {

        System.out.println ("Tried to take too many apples out of the bag!");

    }

}

public class Robot

{

    int val = 0;

    void incVal () { val++; }

    void decVal () { val--; }

    int  getVal () { return val; }

}

Robot r = new Robot();