Why should it build a concrete result?
Here's my reasons why it makes sense to be lazy here:
- It would use more memory otherwise. Since, if you are transforming a list
to a set there's got to a transformed copy of the original data structure
when it's materialized.
- It might take longer than necessary to calculate. Suppose you've threaded
the result into (take n), now, you need to call the predicate of map only n
times.
If you think about large data structures (maybe even infinite sequences),
laziness makes more sense.
On Sat, Feb 8, 2014 at 2:19 AM, Andy C <andy.coolw...@gmail.com> wrote:
> Hi,
>
> I have a short question, why map builds up a LazySeq instead of an input
> collection as found below:
>
> user=> (type (map #(mod % 3) #{3 6}))
> clojure.lang.LazySeq
> user=> (type (map #(mod % 3) '(3 6)))
> clojure.lang.LazySeq
> user=> (type (map #(mod % 3) [3 6]))
> clojure.lang.LazySeq
> user=> (type (map #(mod (% 1) 3) {:a 3, :b 6}))
> clojure.lang.LazySeq
>
>
> One would expect to "(map #(mod % 3) #{3 6})" evaluate into "#{0}". Is it
> arbitrary decision or there is a theory behind it?
>
> Best,
> Andy
>
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Kind Regards,
Atamert Ölçgen
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