t_colon.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.TrinaryOperationException;
import exceptions.TypeMismatchedException;
import java.util.ArrayList;

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

    public Expr reduce(ArrayList<Expr> stack) throws ExpressionException {
        int post=stack.size()-1;  // be?ae:ae
        Expr a=stack.get(post);   // ae
        Expr b=stack.get(post-1);// :
        Expr c=stack.get(post-2);// ae
        Expr d=stack.get(post-3);// ?
        Expr e=stack.get(post-4);//be
        
        if(!(a instanceof ArithExpr) || !(c instanceof ArithExpr)|| !(e instanceof BoolExpr))
            throw new TypeMismatchedException();
        if(!(d.type==Type.qm))
            throw new TrinaryOperationException();
        if(((BoolExpr)e).value==true)
        {
            stack.remove(post);
            stack.remove(post-1);
            stack.remove(post-3);
            stack.remove(post-4);
            return c;
        }
        else
        {
            stack.remove(post-1);
            stack.remove(post-2);
            stack.remove(post-3);
            stack.remove(post-4);
            return a;
        }
    }

}