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

/* Robot Grammar */

%%

program : program line

    | ;

line: NL            { if (interactive) System.out.print (input_str); r.reset(); }

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

                      if (interactive) System.out.print (input_str); r.reset(); };

S : P S T S         { }

    | P S           { }

    |               { };

P : PUT             { System.out.println ("PUT  an apple in the bag"); r.incVal(); };

T : TAKE            { System.out.println ("TAKE an apple out of the bag"); r.decVal(); };

%%

private Yylex lexer;

static boolean interactive = false;

private static String input_str = "Input: ";

private Robot r = new Robot();

public void yyerror (String error)

{

    /* No need to print out anything here, since we'll

     * catch all errors later anyway. */

    //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("[Quit with CTRL-D]");

        System.out.print(input_str);

        interactive = true;

    }

    /* If we have had an error parsing, we probably tried to take too many

     * apples out of the bag, so print out a nice error message. */

    try

    {

        yyparser.yyparse();

    }

    catch (Exception e)

    {

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

    }

    /* Print ending message if we are in interactive mode */

    if (interactive)

    {

        System.out.println();

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

    }

}

/**

 * Private class, which will be used to keep track of how many apples

 * are in the bag. It could possibly be extended later to allow for a

 * graphical reprensentation of the robot.

 */

public class Robot

{

    private int val = 0;

    void incVal () { val++; }

    void decVal () { val--; }

    int  getVal () { return val; }

    void reset  () { val = 0; }

}