public BinopExp(Exp l, Token op, Exp r)
	{
	    Left = l;
	    Right = r;
	    ExpType = typeof(int);
	    
	    switch(op.Type){
	    case TokenType.PLUS:
		Oper = Operator.ADD;
		break;
	    case TokenType.MINUS:
		Oper = Operator.SUB;
		break;
	    case TokenType.MUL:
		Oper = Operator.MUL;
		break;
	    case TokenType.DIVIDE:
		Oper = Operator.DIVIDE;
		break;
	    }
	}
	public CompareExp(Exp l, Token op, Exp r)
	{
	    Left = l;
	    Right = r;
	    
	    switch(op.Type){
	    case TokenType.LT:
		Oper = Operator.LT;
		break;
	    case TokenType.GT:
		Oper = Operator.GT;
		break;
	    case TokenType.EQ:
		Oper = Operator.EQ;
		break;
	    case TokenType.LE:
		Oper = Operator.LE;
		break;
	    case TokenType.GE:
		Oper = Operator.GE;
		break;
	    }
	}