Edward Tate wrote
Are user extensible streams ala: http://www.doc.gold.ac.uk/~mas01cr/papers/ilc2007/sequences-20070301.pdfgoin... to be catered for in cltl3?
(ITYM "extensible sequences", not "extensible streams".)
People who want extensible sequences should implement them for their favorite Open Source implementation, or ask their commercial vendor to do it. (Even if they, the commercial vendors, may not consider it now, expressing your need is important so they will consider it some day.)
The implementation-dependent bits that are needed are not difficult -- and you can borrow the bulk of the implementation (the generic protocol, plus the generic implementation of the sequence functions specified in the standard) just from Christophe Rhodes' code.
The code was placed in the public domain so can also be reused by the commercial vendors without problem.
I'm pretty sure a dedicated hacker will probably be able to do it in the days between the years.
So if you have some free time at hand, and do not know what to do, try it. Fame and glory awaits. :-)
-T.
PS.
The alternative, portable route is described here
http://common-lisp.net/~trittweiler/talks/sequence-iterators-2009.pdf
If you want to help out on that instead, drop me a mail.