Re: Sets and Lists, again

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

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

> 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...

--dawn Received on Sat May 20 2006 - 06:02:57 CEST