This might be too detailed a point, but I wanted to mention that while you will always get the same order for the same collection (same as determined by identical?, or Java ==, i.e. it is the same object in memory), you are *not* guaranteed to get the same order for collections of the same type that are equal to each other as determined by Clojure = or Java .equals. In particular, if two values have the same hash value, then if they are used as a set in a Clojure PersistentHashSet or a key in a PersistentHashKey, they are put into a linear list in a hash bucket for that hash value, and their order in that list can be different in different sets/maps, and the order that (seq ...) returns on those sets/maps will be different.
I am not certain, but this might violate referential transparency (replacing a value that is equals for another value in an expression will always give you an equal result). I was curious whether anyone knows whether Haskell has hash-based data structures like this, and do they somehow guarantee referential transparency? Perhaps by requiring the items to be sortable? Andy On Sat, Feb 8, 2014 at 8:19 AM, Jozef Wagner <jozef.wag...@gmail.com> wrote: > Every persistent collection in Clojure supports conversion to the sequence > of items. This is clearly documented in the official docs and there is no > surprise here. > > The order or items in the resulting sequence is dependent on the > collection type. As the conversion to the sequence is a referentially > transparent function, you will always get the same order for the same > collection. > > JW > > On Saturday, February 8, 2014 4:59:47 PM UTC+1, Andy C wrote: > >> On Sat, Feb 8, 2014 at 12:06 AM, Sean Corfield <se...@corfield.org>wrote: >> >>> But you're misunderstanding what map does: it converts its collection >>> arguments to _sequences_ and then it processes those sequences. Map >>> doesn't operate on sets, or vectors, or maps, only on sequences. >>> >> >> Your assertion that I "am misunderstanding something" is wrong. >> >> One cannot convert amorphic set into linear sequence without assuming >> certain order. And as with every assumption, it always comes with some less >> or more pragmatic but arbitrary decision which might change over time and >> ruin peoples programs. >> >> I would expect Clojure to throw "IllegalArgumentException Don't know how >> to create ISeq from: clojure.lang.PersistentHashSet" or document it well >> in map somewhere. >> >> >> "Perfection is the enemy of the good." >>> >> >> Now judging by your sig, it all does not surprise me LOL >> >> >> >> -- > 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/groups/opt_out. > -- 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/groups/opt_out.
