ArithmeticBuilderIncorrect.java

/*
    BeepBeep, an event stream processor
    Copyright (C) 2008-2018 Sylvain Hallé

    This program is free software: you can redistribute it and/or modify
    it under the terms of the GNU Lesser General Public License as published
    by the Free Software Foundation, either version 3 of the License, or
    (at your option) any later version.

    This program is distributed in the hope that it will be useful,
    but WITHOUT ANY WARRANTY; without even the implied warranty of
    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
    GNU Lesser General Public License for more details.

    You should have received a copy of the GNU Lesser General Public License
    along with this program.  If not, see <http://www.gnu.org/licenses/>.
 */
package dsl;

import java.util.ArrayDeque;

import ca.uqac.lif.bullwinkle.BnfParser.InvalidGrammarException;
import ca.uqac.lif.bullwinkle.Builds;
import ca.uqac.lif.cep.dsl.GrammarObjectBuilder;
import ca.uqac.lif.cep.functions.Constant;
import ca.uqac.lif.cep.functions.Function;
import ca.uqac.lif.cep.functions.FunctionTree;
import ca.uqac.lif.cep.util.Numbers;

/**
 * Shows what happens when a
 * {@link ca.uqac.lif.cep.dsl.GrammarObjectBuilder GrammarObjectBuilder}
 * incorrectly manipulates its object stack.
 * @author Sylvain Hallé
 * @see ArithmeticBuilder
 * @difficulty Medium
 */
public class ArithmeticBuilderIncorrect extends GrammarObjectBuilder<Function>
{
    public static void main(String[] args) throws BuildException
    {
        //&
        ArithmeticBuilderIncorrect builder = new ArithmeticBuilderIncorrect();
        Function f = builder.build("+ 3 - 4 5");
        Object[] value = new Object[1];
        f.evaluate(new Object[]{}, value);
        System.out.println(value[0]);
        //&
    }
    
    
    ///
    public ArithmeticBuilderIncorrect()
    {
        super();
        try
        {
            setGrammar("<exp> := <add> | <sbt> | <num>;\n"
                    + "<add> := + <exp> <exp>;\n"
                    + "<sbt> := - <exp> <exp>;\n"
                    + "<num> := ^[0-9]+;");
        }
        catch (InvalidGrammarException e)
        {
            // Do nothing
        }
    }
    ///

    @Builds(rule="<num>")
    //*
    public void handleNum(ArrayDeque<Object> stack)
    {
        String s_num = (String) stack.pop();
        Number n_num = Float.parseFloat(s_num);
        Constant c = new Constant(n_num);
        stack.push(c);
    }
    //*

    //%
    @Builds(rule="<add>")
    public void handleAdd(ArrayDeque<Object> stack)
    {
        Function f2 = (Function) stack.pop();
        stack.pop(); // Incorrect! This line and the next should be swapped
        Function f1 = (Function) stack.pop();
        stack.push(new FunctionTree(Numbers.addition, f1, f2));
    }
    //%

    //!
    @Builds(rule="<sbt>")
    public void handleSbt(ArrayDeque<Object> stack)
    {
        Function f2 = (Function) stack.pop();
        Function f1 = (Function) stack.pop();
        stack.pop(); // To remove the "-" symbol
        stack.push(new FunctionTree(Numbers.subtraction, f1, f2));
    }
    //!

}