[+srfi-...@srfi.schemers.org] Alex Shinn scripsit:
> The naive approach would be to define ipairs with setters > and simply not export those setters to the user. This runs > into problems with future extensions for record introspection. Hopefully such extensions will make provision for opaque record types on which `record-rtd?` does not work (and `record?` returns #f). > However, using lazy evaluation one could have truly > immutable, portable records and still provide such > utilities as `circular-ilist' and the equivalent of Racket's > `shared'. Sure. But the question is whether such polymorphism is useful, or whether it's better to have a distinct type of immutable cycles, either one-way or (per CyclesMedernach) two-way. The only SRFI 1 procedures that apply equally to circular and normal lists are list-ref, length+ (aka R7RS length), zip, count, fold(-right), pair-fold(-right), map, for-each, append-map, map-in-order, pair-for-each, filter-map, find(-tail), take-while, drop-while, span, break, any, every, list-index. Most of these accept multiple lists, of which at least one must be finite, so for example you cannot map a procedure over a circular list and get a circular list. Having to be prepared to handle promises at any point will make all these functions slower on normal ilists. -- John Cowan http://www.ccil.org/~cowan co...@ccil.org Most people are much more ignorant about language than they are about [other subjects], but they reckon that because they can talk and read and write, their opinions about talking and reading and writing are as well informed as anybody's. And since I have DNA, I'm entitled to carry on at length about genetics without bothering to learn anything about it. Not. --Mark Liberman _______________________________________________ Scheme-reports mailing list Scheme-reports@scheme-reports.org http://lists.scheme-reports.org/cgi-bin/mailman/listinfo/scheme-reports
