Hi, On 3 Sep., 11:16, Abraham Varghese <abev...@gmail.com> wrote:
> I cannot understand between ( next aseq) and ( rest aseq) ... next will realise the first item of the rest of aseq, while rest will not. You can always express next in terms of rest: (defn next [s] (seq (rest s))) Sometimes you can also express rest in terms of next: (defn rest [s] (or (next s) ())) However this will not work for lazy sequences as returned by filter or map since here the next item will be immediately realised. The reason for this realisation is, that next returns nil when the sequence is exhausted. However in order to be able to return nil you have to know whether are actually no more items in the sequence. So you have to realise it. The advantage is, that you can use next as a predicate in if or when. The disadvantage is that you are not completely lazy. That's why rest was introduced (actually: rest was renamed to next and new rest was introduced). It allows to return a value which decides whether it's nil or not only when you call seq on it. Usually you want to use rest. next is useful in loops, where you often test on whether the sequence is exhausted (there it saves seq calls). Or when you know you'll need the first item of the resulting sequence anyway. Hmm.. I'm not sure, I understand my exlpanation myself. Hope it helps anyway. Sincerely Meikel -- 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 Note that posts from new members are moderated - please be patient with your first post. 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
