First have a look at delay (and clojure.lang.Delay) and try to understand it. LazySeq is just a delay with a fancy interface (supporting seq, first and rest). There is no recursion per se in the LazySeq object. What makes it harder to understand is the idiom of using lazy-seq together with cons and recursion, as seen e.g. in following range-like function:
(defn range* [from] (lazy-seq (cons from (range* (inc from))))) user=> (set! *print-length* 10) 10 user=> (range* 0) (0 1 2 3 4 5 6 7 8 9 ...) Similar function with delay would be (defn range* [from] (delay [from (range* (inc from))])) user=> (range* 0) #<Delay@7c5ff8ce: :pending> user=> @(range* 0) [0 #<Delay@19c6a644: :pending>] user=> (first @(range* 0)) 0 user=> (second @(range* 0)) #<Delay@672f151d: :pending> user=> @(second @(range* 0)) [1 #<Delay@3e6dac3d: :pending>] user=> (first @(second @(range* 0))) 1 ... Jozef On Sun, Apr 6, 2014 at 6:56 PM, sorin cristea <srncris...@gmail.com> wrote: > > Hi, > > maybe this question was already put it here, but can someone explain how > exactly work internal a function wrapped with lazy-seq keyword. For example > in the below code sample: > > ( > defn test-fc > "sum of all collection elements using recursion and laziness" > [coll] > (letfn [(sum-fc [sum coll] > (if (empty? coll) > (cons sum nil) > (lazy-seq(sum-fc (+ sum (first coll)) (rest coll)))) > > ) > ] > (sum-fc 0 coll) > ) > ) > > if I test the function: (test-fc (range 5)) I got the right result, if I > continue to test with bigger number I don't got StackoverflowException, but > if run (test-fc (range 210432423543654675765876879)) I didn't get > StackoverflowEx but the application didn't return any result, because take > to much time to compute this ? > > How exactly work this internally and how is removed recursion( inside call > sum-fc with new parameters) from the flow in this case ? From what I saw in > java code of LazySeq class and clojure source code, it's made a list with > LazySeq object and in my opinion in that list the LazySeq object contain > enough information to compute the requested item and in this way is removed > recursion and implicit StackoverflowException issue, if I understand > something wrong please explain to me. > I test this function from IntellijIDEA + LaClojure plugin. > > Thanks > Sorin. > > -- > 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. > -- 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.
