I'm pretty much finished with the fully-lazy implementation and am happy so far with the results. I think this will be an important addition to Clojure and am planning to add it.
Now comes the hard part - names and change. The essence of the fully lazy seqs is that they will not consume any resources, perform any computation or trigger any side effects until they are consumed. This is a change to the way the sequence functions work now, in that, in order to determine whether they should return a seq or nil, they need to touch at least one item. So, there will be an additional function on seqs, one that returns the items other than the first as a logical, non-nil, possibly empty collection. Calling seq on this collection will give you what rest currently gives you - the next seq object or nil if none. So the core operations on seqs will be: ;item (first x) ;collection of remaining items, possibly empty (possibly-empty-collection-of-the-remaining-items x) ;seq on next item, or nil if none (seq-on-the-next-item-if-any-else-nil x) (first x) is uncontroversial and won't change. The second is a new function. The third is currently called 'rest'. I have some ideas for names, and there are definitely tradeoffs between short-term pain and long-term goodness in some of the options. The first option is to leave rest alone, and give the new function a new name, like more. ;item (first x) ;collection of remaining items, possibly empty (more x) ;seq on next item, or nil if none (rest x) Note that (rest x) === (seq (more x)) This is implemented in the lazy branch, SVN rev 1281. It has the attribute of requiring the fewest changes to existing code, and the drawback of leaving us with less-than-ideal names, especially insofar as more (or whatever you choose to call it) will in some way seem synonymous with rest. This naming scheme, and the changes it implies, is documented here: http://clojure.org/lazier1 The second option is to choose the best possible names, and deal with some short term pain in porting and confusion. I think the best names are: ;item (first x) ;collection of remaining items, possibly empty (rest x) ;seq on next item, or nil if none (next x) This is implemented in the lazy branch, SVN rev 1282. Note that this changes the meaning of rest, and gives the current rest operation a new name, next. It has the attributes of using the most appropriate names (IMO) and the drawback of changing the semantics of a frequently used function name, but still offering that functionality under a different name. It would also break the compatibility of rest with Common Lisp's. As with the previous model, the third function can be defined in terms of the second - (next x) === (seq (rest x)). This naming scheme, and the changes it implies, is documented here: http://clojure.org/lazier A third option would be to retire rest and use only new names: ;item (first x) ;collection of remaining items, possibly empty (more x) ;seq on next item, or nil if none (next x) I haven't implemented this. I prefer first/rest/next. I think rest is the best complement to first, and it should mean the logical collection once things are fully lazy. I think next implies the next seq, as well as the eager nature of the operation. I am looking for feedback from people willing to read and understand the linked-to documentation and the fully lazy model, and especially from those trying the lazy branch code and porting some of your own. Questions on the model welcome as well. Chouser has also blogged a bit about this, with some useful descriptions of nil punning: http://blog.n01se.net/?p=39 I've been working on this for a few months, in lieu of more interesting things, because I knew it would be a breaking change and we're trying to get the biggest of those behind us. I appreciate any effort you spend in trying to provide informed input. Thanks, Rich --~--~---------~--~----~------------~-------~--~----~ You received this message because you are subscribed to the Google Groups "Clojure" group. To post to this group, send email to clojure@googlegroups.com To unsubscribe from this group, send email to clojure+unsubscr...@googlegroups.com For more options, visit this group at http://groups.google.com/group/clojure?hl=en -~----------~----~----~----~------~----~------~--~---
