Brian Hurt <bhur...@gmail.com> writes: > I will note that vec and set both behave differently- when handed an empty > sequence they don't return nil, they return the (not nil) empty vector or set > (respectively). The specific behavior of seq being depended upon in this case > is different between seq and other, similar-purpose functions.
As Kevin mentioned, part of it historical, there used to be no empty seqs: http://clojure.org/lazy Note also that vec and set are quite different functions to seq, they take a sequence and create a *new* collection of a specific type containing the elements of that sequence: (let [v [1 2 3]] (identical? v (vec v))) ;;=> false (let [s '(1 2 3)] (identical? s (seq s))) ;;=> true (let [v [1 2 3]] (identical? v (seq v))) ;;=> false Seq on the other hand yields an ISeq "view" of a Seqable collection or other seqable object (eg a String). For objects that *are* already non-empty seqs like lists, lazy-seqs and ranges it just returns the object. Note that a seq is not necessarily a persistent list. The list equivalent to the vec or set functions is (apply list ...) -- there's no shorthand for it as you shouldn't be using lists much explicitly, use a vector instead. This might seem like a subtle distinction, but it's quite important. For example map and reduce are seq functions, while get and conj are collection functions. Usually collection functions take the collection as their first argument while seq functions take the seq as their last argument. -- 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
