One nuance to consider re: self-sequable datastructures is that on eval clojure will assume the first element is invocable, see
https://github.com/ztellman/clj-tuple/issues/5 On Wed, Sep 3, 2014 at 1:51 PM, Karsten Schmidt <i...@toxi.co.uk> wrote: > Thanks, Kovas! I looked at it a few months ago (and now just forked > it), but Zach also seems to have created a separate deftype just to > support this conj-ing business (and that alone is 180 LOC...) That all > seems to be a huge effort though and am wondering about simpler > alternatives and/or some better detailed documentation about these > matters and inter-relationships. IMHO this part of Clojure seems to be > very cryptic to me... Just would like to know if this particular > combination of vector-style conj behavior & being self-seqable is > fundamentally incompatible or if I'm missing something here? Of > course, an easy solution would be to just do this: > > (deftype Foo [a b] > (cons [this c] (seq [a b c]))) > > ..but that would mean any further conj-ing will happen at the head. > cons as defined in IPersistentCollection has IPersistentCollection as > return type (and hence would be satisfied by PersistentVector), but > it's being overridden in ISeq and so wins... > > Makes me wonder why conj has not been kept internally separate from > cons. Wouldn't this have avoided this potential for such a conflict? > > > On 3 September 2014 18:33, kovas boguta <kovas.bog...@gmail.com> wrote: >> Not a direct answer but you might want to look at >> >> https://github.com/ztellman/clj-tuple/blob/master/src/clj_tuple.clj >> >> >> >> On Wed, Sep 3, 2014 at 1:13 PM, Karsten Schmidt <i...@toxi.co.uk> wrote: >>> Hi all, >>> >>> I've defined a custom vector type and implemented various clj/cljs >>> protocols, but now ended up hitting my head against some weird behaviour >>> with conj (or rather cons, internally). The type >>> defines a 2-element vector-like construct and my cons >>> implementation would simply return a standard >>> clojure.lang.PersistentVector with the given arg added like this: >>> >>> (deftype Foo [a b] >>> clojure.lang.IPersistentCollection >>> clojure.lang.Indexed >>> clojure.lang.Sequential >>> clojure.lang.ISeq >>> clojure.lang.Seqable >>> clojure.lang.Reversible >>> ;; ... elided seq fn impls... >>> (cons [_ c] [a b c])) >>> >>> However, attempting a conj results in an exception I don't understand: >>> >>> (conj (Foo. 1 2) 3) >>> java.lang.ClassCastException: clojure.lang.PersistentVector cannot be >>> cast to clojure.lang.ISeq >>> at user.Foo.cons (foo.clj:13) >>> user.Foo.cons (foo.clj:-1) >>> clojure.lang.RT.conj (RT.java:562) >>> clojure.core$conj.invoke (core.clj:83) >>> ... >>> >>> As far as I can tell, clojure.core/conj simply calls RT.conj(coll, x), >>> which just calls >>> coll.cons(x): >>> >>> https://github.com/clojure/clojure/blob/master/src/jvm/clojure/lang/RT.java#L604 >>> >>> static public IPersistentCollection conj(IPersistentCollection coll, Object >>> x){ >>> if(coll == null) >>> return new PersistentList(x); >>> return coll.cons(x); >>> } >>> >>> So where in that call path is there an attempt or requirement to cast >>> to an ISeq? >>> >>> I've been comparing notes (as far as this possible) with the default >>> PersistenVector implementation, but not sure where I'm going wrong >>> here... >>> >>> -- >>> 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. >> >> -- >> 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. > > > > -- > Karsten Schmidt > http://postspectacular.com | http://toxiclibs.org | http://toxi.co.uk > > -- > 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. -- You received this message because you are subscribed to the Google Groups "Clojure" group. 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