[cdr-discuss] What about CDR 3, then?

[Gary King]

Hi Christophe,

As an open ended question: how does this CDR relate to Marco  
Antoniotti's CL-Enumerations and my CL-Containers? From an  
implementation point of view, it sounds like you would need to make  
the various CL functions into generic functions and/or write a lot of  
code that dispatches on type within the CL functions.

thanks,



On Dec 3, 2006, at 9:50 AM, Christophe Rhodes wrote:

> Pascal Costanza <pc at p-cos.net> writes:
>
>> To be more concrete: You could regard lazy lists and streams as kinds
>> of sequences, and they could indeed be made subtypes of 'sequence. In
>> those cases, though, it doesn't make a lot of sense that concatenate-
>> sequence supports them, for example, especially when they model
>> infinite sequences (like "all prime numbers", or so).
>
> I agree that infinite sequences aren't amenable to being termed CL
> sequences, because one of the things that a CL sequence has is a
> length, which must be a non-negative integer.  So, indeed, things with
> infinite size aren't sequences.  But that doesn't stop all sorts of
> other things from being sequences: even a class of lazy list which
> knows its length (but not its elements) in advance.  I don't know how
> useful one of the latter would be, I admit.
>
>> I think a different way to say this is as the following question:
>> What guarantees do the existing sequence functions give us? For
>> example, do they have to terminate?
>
> Yes, modulo the usual constraints about the resource limits of the
> physical hardware that might prevent them from doing so.
>
>> What other kinds of subtypes of sequence do you have in mind?
>
> Briefly, off the top of my head: other sequential data structures,
> such as doubly-linked lists, queues, hash-consed lists and
> flexichains; then also application-specific data structures, such as
> editor buffers, HTML DOM elements in a document, compiler blocks in an
> intermediate representation for a program; maybe also system objects
> like memory-mapped files.  I could probably go on :-)
>
> The point of making these sequences is that then these objects can be
> used as arguments to the standard CL functions: you don't have to
> reimplement the whole (or even part) of the sequence library yourself;
> you can simply call functions which express what you mean.  (In some
> cases above, some sequence operations may not make conceptual sense --
> for instance, you're unlikely to want to call SORT on compiler blocks
> -- but that's not to say that the operation doesn't make sense on the
> data structure itself, only on its contents when considered
> semantically from the application point of view.)
>
> I have prepared a paper discussing these and other issues (including
> implementational issues) whose publication I am trying to arrange;
> when I hear back from the ILC program committee about my grossly
> over-the-page-limit proposal, I may be in a position to disseminate
> code and documentation more widely.
>
> Cheers,
>
> Christophe
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