thank Guru,the solution of my problem may not difficult,I first didn't understand the usage of cons and conj,now I can grasp them deeper than before. Clojure is so flexible that it both have cons and conj for different situation,which accounts for its advantages over mit-lisp.
On Friday, April 25, 2014 12:59:34 AM UTC+8, Guru Devanla wrote: > > Another option is to explore "concat" > > > On Thu, Apr 24, 2014 at 8:46 AM, Jiacai Liu <[email protected]<javascript:> > > 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]>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]>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] >>>>> 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] 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.
