t_relation.java

来自「中山大学编译原理课程的一个实验」· Java 代码 · 共 53 行

/*
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 * and open the template in the editor.
 */

package symbols;

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

/**
 *
 * @author Beeven
 */
public class T_RELATION 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.relation)) throw new MissingOperandException();
        if(!(a instanceof ArithExpr) || !(b instanceof ArithExpr))
            throw new TypeMismatchedException();
        BoolExpr be=null;
        switch(o.tag)
        {
            case Tag.EQ:
                be=new BoolExpr(((ArithExpr)a).value==((ArithExpr)b).value); break;
            case Tag.NE:
                be=new BoolExpr(((ArithExpr)a).value!=((ArithExpr)b).value); break;
            case Tag.LE:
                be=new BoolExpr(((ArithExpr)a).value<=((ArithExpr)b).value); break;
            case Tag.LT:
                be=new BoolExpr(((ArithExpr)a).value<((ArithExpr)b).value); break;
            case Tag.GE:
                be=new BoolExpr(((ArithExpr)a).value>=((ArithExpr)b).value); break;
            case Tag.GT:
                be=new BoolExpr(((ArithExpr)a).value>((ArithExpr)b).value); break;
        }
        stack.remove(post);
        stack.remove(post-1);
        stack.remove(post-2);
        stack.add(be);
        return be;
        
    }

}