Hello Rich, I'll play around with the lazy branch this week, and this is just a name suggestion: what do you think of first/tail/rest where (rest s) == (seq (tail s))? tail is already used in other functional languages such as Haskell and OCaml to represent all-but-the-first elements, so it wouldn't be completely foreign.
Vincent. On Feb 15, 12:18 pm, Rich Hickey <richhic...@gmail.com> wrote: > 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 -~----------~----~----~----~------~----~------~--~---
