On Feb 17, 2009, at 4:40 AM, Konrad Hinsen wrote:
> > On Feb 16, 2009, at 20:23, Rich Hickey wrote: > >> It seems the Sequence/ISeq dichotomy was a sticking point for many. >> After some tweaking, I've been able to get rid of Sequence entirely, >> SVN 1284+ in lazy branch. This is source compatible with 1282 (first/ >> rest/next), except that sequence? no longer exists - go back to seq?. >> >> New docs here: >> >> http://clojure.org/lazy >> >> Let me know if that is simpler. > > I'd say yes. > > The remaining weird feature is the seq function and its use. The name > suggests that it converts to a seq, which is in fact what it used to > do. Now it converts to a seq unless the resulting seq would be empty. > For an empty seq, it actually converts a seq to a non-seq! > There will always be a tension between treating the first node in a list as a node vs as the entire list. The seq function is firmly in the former camp, essentially returning the node containing the first item. seq also has an important role regarding lazy seqs - when given one it forces it and returns the inner seq. This is the big reason why empty? is not a replacement for seq. One way to look at (seq x) is as a version of (not (empty? x)), where the truth value is more useful than 'true'. I will be adding a sequence function that will act as a constructor/ coercion, so: (seq []) -> nil (sequence []) -> () In addition, sequence, when given a seq, will not force it, if it is lazy. It will work like this: (defn sequence [x] (if (seq? x) x (or (seq x) ()))) People that don't like nil punning need never use seq/next. > Would it be possible to make an empty seq test as false? No - then you could no longer distinguish between an empty collection and nothing. Additionally, that would be a big performance hit for 'if'. 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 -~----------~----~----~----~------~----~------~--~---
