Re: Sets and Lists, again

"dawn" <dawnwolthuis_at_gmail.com> wrote in message news:1148097777.431200.106670_at_j55g2000cwa.googlegroups.com...
> David Cressey wrote:
> > Recently, in a thread on implementing both threads and lists in a
> > programming language, the example of lists or sets of Presidents arose.
I
> > mentioned that in a list of presidents, Grover Cleveland would appear
once,
> > but in a list of presidencies, he would appear twice.
> >
> > Bob Badour asked what purppose would be served by a list of presidents,
or
> > words to that effect. I'm interested.
> >
> > If one could have a set of presidents, why would one ever want a list?
>
> president[40]
>
> > In
> > general, if a language implements sets, why would the same language
need
> > to also implement lists? What does it buy you?
>
> ripple delete of frames 105 - 140; insert of these songs in the
> playlist at this point
>

What's a ripple delete? How is it different from an ordinary delete?

> Obviously you can hand-code these functions, but why should you have
> to?

If you have sets, why would you have to "insert at this point"?

>
> > I'm thinking of Lisp, which implemented lists, but not sets. MDL (aka
> > Muddle) implemented arrays, and that's one step closer to implementing
sets,
> > but not all the way.
> >
> > SQL implemented sets, but not lists. Although local extensions of SQL
do
> > implement lists, e.g. "Segmented Strings" in DEC Rdb (aka Oracle/Rdb),
> > it's not really part of the language as such.
> >
> > I'm also thinking of Pascal, which implemented sets, (as bitmaps), and
also
> > lists, albeit implicitly. What I mean is that you can combine the
concepts
> > of "record" and "pointer" in Pascal to construct dynamic linked lists of
> > whatevers. But Pascal was primarily for teaching and learning
programming,
> > and may have implemented both for precisely that purpose.
> >
> > So, if you have sets, why do you need lists?
>
> In order to take common functions and include them in a dbms library.
> It is the same reason for any reusable code. These functions include
> those mentioned by Marshall in another thread (e.g. zip), ripple
> delete, insert, select nth item in list...
>

Why do you need lists for this purpose? Received on Sat May 20 2006 - 13:07:47 CEST