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@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 _______________________________________________ cdr-discuss mailing list cdr-discuss@common-lisp.net http://common-lisp.net/cgi-bin/mailman/listinfo/cdr-discuss
-- Gary Warren King, metabang.com Cell: (413) 885 9127 Fax: (206) 338-4052 gwkkwg on Skype * garethsan on AIM