I think you’ve actually answered your own question without realizing it. At least, the way I was taught is that “conj” is always constant time w.r.t. the collection being appended to. Since different collections have different internal storage mechanisms, that means that “conj” will do different things for different collections. Specifically, since a “list” is implemented as a linked-list, appending to the front is constant time. However vectors, which are backed by Java arrays, can only do a constant-time append by adding to the end.
On Thursday, April 24, 2014 at 18:46, Jiacai Liu wrote: > Well,I understand you. > list only support front insert since it only takes O(1). > If insert in the back,it would require O(n) time. > Maybe clojure has its own reasons for having both cons and conj. > Thank again for telling me their differences. > > On Thursday, April 24, 2014 11:36:13 PM UTC+8, Gary Trakhman wrote: > > Well, maybe I shouldn't bash MIT-scheme unintentionally :-). I bet some > > people use it for serious stuff, and I have no bad experiences with it. > > > > > > On Thu, Apr 24, 2014 at 11:33 AM, Gary Trakhman <[email protected] > > (javascript:)> wrote: > > > MIT-lisp is more for teaching than industrial use.. > > > > > > We also have hash-maps, vectors, sets, queues, conj works with all of > > > them, leaving the details up to the collection. > > > > > > Cons always adds to the front. Conj only adds to the back for certain > > > collections (vector, queue). > > > > > > You could work around it by reversing, consing, then reversing again, or > > > just use vectors and conj if you're always working on the tail. > > > > > > > > > On Thu, Apr 24, 2014 at 11:27 AM, Jiacai Liu <[email protected] > > > (javascript:)> wrote: > > > > Oh,Thank you for answer. > > > > But if I just want to insert a element to list,and meantime want to > > > > insert in the back.How should I do? > > > > Another question: why clojure need both cons and conj? In mit-lisp cons > > > > just do all things. > > > > > > > > > > > > On Thursday, April 24, 2014 11:12:49 PM UTC+8, Gary Trakhman wrote: > > > > > Conj is polymorphic on its first argument. If you pass it a vector, > > > > > it'll add to the back, if a list, the front. The collection is > > > > > responsible for deciding the most efficient way to add an element. > > > > > > > > > > Cons always adds to the front, creating a linked-list node pointing > > > > > to the rest. Also, cons takes the sequence as the second argument. > > > > > > > > > > > > > > > On Thu, Apr 24, 2014 at 11:10 AM, Jiacai Liu <[email protected]> > > > > > wrote: > > > > > > hi everyone: > > > > > > I use Clojure to solve SICP 2.22 > > > > > > (http://www.billthelizard.com/2011/01/sicp-221-223-mapping-over-lists.html). > > > > > > The problem is to rewrite a map fn in a iterative way，here it want > > > > > > to get the square of each element in a list > > > > > > Method 1: > > > > > > (defn square-list [items] > > > > > > (defn iter [things answer] > > > > > > (if (empty? things) > > > > > > answer > > > > > > (iter > > > > > > (rest things) > > > > > > (cons (square (first things)) answer)))) > > > > > > (iter items nil)) > > > > > > > > > > > > This method just return opposite result. > > > > > > (square-list (range 1 10)) > > > > > > ;===>(81 64 49 36 25 16 9 4 1) > > > > > > > > > > > > I think all I need is to swap the position of (square (first > > > > > > things)) and answer,then I can get the right order > > > > > > I write fn below: > > > > > > Method 2 > > > > > > (defn square-list [items] > > > > > > (defn iter [things answer] > > > > > > (if (empty? things) > > > > > > answer > > > > > > (iter > > > > > > (rest things) > > > > > > (conj answer (square (first things)))))) > > > > > > (iter items nil)) > > > > > > > > > > > > However, it still return opposite order. > > > > > > Did I misuse cons and conj or I ignore something? > > > > > > > > > > > > > > > > > > -- > > > > > > You received this message because you are subscribed to the Google > > > > > > Groups "Clojure" group. > > > > > > To post to this group, send email to [email protected] > > > > > > > > > > > > Note that posts from new members are moderated - please be patient > > > > > > with your first post. > > > > > > To unsubscribe from this group, send email to > > > > > > [email protected] > > > > > > > > > > > > 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 [email protected]. > > > > > > > > > > > > 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 [email protected] > > > > (javascript:) > > > > Note that posts from new members are moderated - please be patient with > > > > your first post. > > > > To unsubscribe from this group, send email to > > > > [email protected] (javascript:) > > > > 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 [email protected] (javascript:). > > > > 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 [email protected] > (mailto:[email protected]) > Note that posts from new members are moderated - please be patient with your > first post. > To unsubscribe from this group, send email to > [email protected] > (mailto:[email protected]) > 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 [email protected] > (mailto:[email protected]). > 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 [email protected] Note that posts from new members are moderated - please be patient with your first post. To unsubscribe from this group, send email to [email protected] 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 [email protected]. For more options, visit https://groups.google.com/d/optout.
