On Sunday, June 12, 2016 at 12:41:05 AM UTC-4, Alex Miller wrote: > > > > On Saturday, June 11, 2016 at 6:33:07 PM UTC-5, Fluid Dynamics wrote: >> >> On Saturday, June 11, 2016 at 6:55:03 PM UTC-4, Matching Socks wrote: >>> >>> pop isn't a sequence function. >>> >>> Check out the manual: >>> http://clojure.github.io/clojure/clojure.core-api.html#clojure.core/pop >>> <http://www.google.com/url?q=http%3A%2F%2Fclojure.github.io%2Fclojure%2Fclojure.core-api.html%23clojure.core%2Fpop&sa=D&sntz=1&usg=AFQjCNHBkrZNW1WA3Vf7Umyqq4KVNK6cEQ> >>> >>> You may use first/rest on any sequence, but pop does something more >>> special(ized). >>> >> >> Well, I see push/pop/peek as like conj, except not applicable to >> non-ordered (set, map) or non-arbitrarily-ordered (sorted-set, sorted-map) >> collections. Should work with all linear arbitrarily-ordered >> order-preserving colls that have an efficient trio of add/examine/drop-one >> at one end or the other. >> > > Clojure distinguishes between collection functions (which take and return > a collection instance) and sequence functions (which take and return a > seqable). Currently pop/peek are defined specifically for persistent > collections (list, queue, and vector) as mentioned in the doc string. > > I can see how pop/peek could be considered as sequence ops too as they map > basically to first/rest. I don't know that I've ever heard a justification > for this, but my guess would be that they differ based on what you should > expect based on efficiency. With a collection, you know the data already > exists and peek can return it in constant time. Similarly, pop can > efficiently return to you the remainder of the collection. > > Sequences however are potentially lazy and an open abstraction. While > calling first seems like a fast operation, in a lazy sequence you might be > calling a database to retrieve a row or hitting a file system to retrieve a > file or a line. Similarly, calling rest may also require the first item to > be realized if the elements are being read from a serialized source. > > One (common) approach when building a collection library is to build a > very rich generic API. Ultimately you will have implementations that either > fail to implement certain operations or back-fill them with inefficient > implementations. Clojure instead chooses to define many "traits" or slices > of functionality, set performance expectations for the ops in those traits, > and implement them only where those expectations can be met. > > The former approach feels more "complete" as a user but only by lying > about what its data structures can do. This ultimately means that when you > see a call to a collection operation, you must either have no expectation > about its performance or you must understand at a deeper level what > implementation you are actually using and what it will do. Clojure's > approach allows you to instead make assumptions about the performance of an > operation and know that when the call doesn't work, that's probably why > (and perhaps you need to revisit what data structures you are using). If > it's not too cliche, this is a textbook choice of easy vs simple. > > You haven't actually said what problem you're trying to solve. If the > problem is choosing a data structure to act as a stack, then I would > recommend choosing one of the collections that implements the stack API. >
All of that is very interesting, but then, by your own arguments (pop (seq '(1 2 3))) should *not* work. -- 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.
