Re: Sets and Lists, again

David Cressey wrote:
> "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?

http://www.tincat-group.com/mewsings/2006/01/who-ordered-ripple-delete.html

> > 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?

? Why do you need lists for the purpose of having list operators? Can you rephrase?
--dawn Received on Sat May 20 2006 - 15:38:30 CEST