t_andor.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.MissingOperandException;
import exceptions.TypeMismatchedException;
import java.util.ArrayList;

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

    public Expr reduce(ArrayList<Expr> stack) throws ExpressionException {
        int post=stack.size()-1;
        
        Expr a=stack.get(post-2);
        Expr o=stack.get(post-1);
        Expr b=stack.get(post);
        if((b.type==Type.and)||(b.type==Type.or)) throw new MissingOperandException();
        if(!(a instanceof BoolExpr) || !(b instanceof BoolExpr))
            throw new TypeMismatchedException();
        BoolExpr be;
        if(o.tag==Tag.AND)
            be=new BoolExpr(((BoolExpr)a).value && ((BoolExpr)b).value);
        else
            be=new BoolExpr(((BoolExpr)a).value || ((BoolExpr)b).value);
        stack.remove(post);
        stack.remove(post-1);
        stack.remove(post-2);
        stack.add(be);
        return be;
    }

}