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

%token NL

%token RESET

/* Robot Grammar */

%%

program : program line

    | ;

line: NL        { if (interactive) System.out.print ("Line: "); }

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

                  if (interactive) System.out.print ("Line: "); }

    | RESET     { r.reset(); System.out.println ("Reset the robot"); };

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;

static boolean interactive = false;

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

{

    Parser yyparser = null;

    if (args.length > 0)

    {

        // read via file argument

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

    }

    else

    {

        // interactive mode

        yyparser = new Parser (new InputStreamReader (System.in));

        /*

        System.out.println ("Specify the file to use as the first command-line");

        System.out.println ("option. (EX: java Parser filename.txt)");

        System.exit (1);

        */

        System.out.println("[Quit with CTRL-D]");

        System.out.print("Expression: ");

        interactive = true;

    }

    try

    {

        yyparser.yyparse();

    }

    catch (Exception e)

    {

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

    }

    if (interactive)

    {

        System.out.println();

        System.out.println("Have a nice day");

    }

}

public class Robot

{

    int val = 0;

    void incVal () { val++; }

    void decVal () { val--; }

    int  getVal () { return val; }

    void reset  () { val = 0; }

}

Robot r = new Robot();