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 <jiaca...@gmail.com<javascript:> > > 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)) >> andanswer,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 clo...@googlegroups.com<javascript:> >> Note that posts from new members are moderated - please be patient with >> your first post. >> To unsubscribe from this group, send email to >> clojure+u...@googlegroups.com <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 clojure+u...@googlegroups.com <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 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.
