From lliao@ren.eecis.udel.edu Sat Oct 12 23:31:19 2002
Date: Sat, 12 Oct 2002 23:30:39 -0400 (EDT)
From: Li Liao <lliao@ren.eecis.udel.edu>
To: Hyunok Park <hpark@udel.edu>
Subject: Re: question for hw2




> >
> > Your initial state ([], []) is not right. The dictionary stack cannot be
> > empty; it must have at least one dictionary, even if that dictionary
> > may be empty (and it should be empty at the beginning)
> >
>
> Actually, that's what I was about to ask you right after I sent you
> previous email. How do I initialize the dictionary at the very begining (
> an empty dictionary)?

Please take a look at the sample code from lecture 8 (posted as message 12
on the bboard) to see how to initialize a dict as empty.

>
>
> According to the homework sheet, begin saves the current bindings. It
> seems to me that begin doesn't do anything until end comes up. When end
> comes up, then I just go back to previous bindings. Is that right?
>

It is right. But do you know how to "save the current bindings"?
Certainly it will do any good if "begin doesn't do anything".
Also I hope you understand what you should do when you then
"just go back to previous bindings."
Think hard why we have a stack of dictionaries instead of just
one dictionary, and what operations we have for a stack?
I hope this hint will bring you to the answer.


Li