Functions like map/filter/remove are not "collection functions" but rather "sequence functions." The collection functions like conj preserve the type of their argument. Sequence functions, by contrast, coerce any argument to a sequence, and always return a sequence.
Since Clojure 1.7, transducers provide a convenient way to compose sequence-like operations but produce a non-sequence as a result: user=> (into [] (comp (map inc) (filter even?)) [1 2 3 4 5]) [2 4 6] mapv and filterv were convenience functions added before the introduction of transducers, as I recall. –S On Friday, September 9, 2016 at 6:23:37 AM UTC-4, Colin Yates wrote: > > Hi all, > > So in the spirit of exposing my ignorance to the internet :-), I have just > been bitten by a bug due to the behaviour of the core libraries which I > find really surprising: > > (def v [1 2 3]) > (conj v 4) => [1 2 3 4] > (conj (map identity v) 4) => (4 1 2 3) > (conj (remove (constantly false) v) 4) => (4 1 2 3) > (conj (filter identity v) 4) => (4 1 2 3) > > In other words, I was relying on map, remove and filter preserving the > semantics (other than laziness) of the structure of the input, give it a > vector and you get a vector-like lazy sequence. This turns out not to be > the case. > > Now, I know there is mapv which returns a vector but why isn't there a > removev and a filterv etc.? > > What makes it more onerous for me is the fact conj states that its > behaviour differs depending on the concrete type, which is great, but how > am I supposed to know which concrete type is returned from > map|filter|remove? My assumption was it would be semantically equivalent to > the input (i.e. a vector in this case). > > The reason I have dodged this is because I don't frequently rely on vector > semantics but I am surprised this isn't better documented? > > Is it me? > > Thanks, > > Colin > -- 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 --- You received this message because you are subscribed to the Google Groups "Clojure" group. To unsubscribe from this group and stop receiving emails from it, send an email to clojure+unsubscr...@googlegroups.com. For more options, visit https://groups.google.com/d/optout.
