t_neg.java

中山大学编译原理课程的一个实验

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package symbols;

import exceptions.ExpressionException;
import exceptions.TypeMismatchedException;
import java.util.ArrayList;

/**
 *
 * @author Beeven
 */
public class T_NEG extends Terminal implements TerminalReduce{

    public Expr reduce(ArrayList<Expr> stack) throws ExpressionException {
        int post=stack.size()-1;
        Expr a=stack.get(post);
        if(!(a instanceof ArithExpr)) throw new TypeMismatchedException();
        double v =((Num)a.token).value;
        ArithExpr ae = new ArithExpr(-v);
        stack.remove(post);
        stack.remove(post-1);
        stack.add(ae);
        return ae;
    }

}