->> and -> actually play nice with each other in this direction:
(-> 4
range
(->> (map inc))
last)
results in 4, because we end up with (-> (range 4) (->> (map inc)) last)
--> (-> (->> (range 4) (map inc)) last) --> (last (->> (range 4) (map
inc))) --> (last (map inc (range 4))). Though all this saves you is a
single function call, and flip is a useful thing to have around anyway.
btw, as far as "flip", you don't need the "into" call; you can just do:
(defn flip [f] (fn [x y & args] (apply f y x args))
though I don't know how if this is actually significant.
On Thu, Apr 30, 2015 at 3:47 PM, Vagmi Mudumbai <[email protected]> wrote:
> Hi,
>
> I was introducing one of my colleagues to clojure[1] and we were
> trying to parse the reddit json as an exercise.
>
> (require '(clj-http.client :as client))
> (require '(clojure.data.json :as json))
>
> (def ^:const REDDIT-URL "http://reddit.com/r/clojure.json?limit=100";)
> (def ^:const headers {:headers {"User-Agent" "showoffclojure.core by
> vagmi"}})
>
> (let [entries_ (-> REDDIT-URL
> (client/get headers)
> (:body)
> (json/read-str :key-fn keyword)
> (:data)
> (:children))]
> (map :data entries))
>
> It would have been nice if we were able to write the map as a part of
> the threading macro. So if there were a flip function like in haskell,
> we could flip the args to the function hand have the map in the
> threading macro. I could not find one so I wrote one.
>
> (defn flip [fn_]
> (fn [x y & args]
> (apply fn_ (into [y x] args))))
>
> Now I can bring in the map as a part of the -> threading macro.
>
> (-> REDDIT-URL
> (client/get headers)
> (:body)
> (json/read-str :key-fn keyword)
> (:data)
> (:children)
> ((flip map) :data))
>
> This seems to be rather easy and useful and gets rid of the let block.
> Are there any implications to performance or impact to laziness by
> using flip? This would be useful even on the transduced version of
> map like ((flip transduce) (map :data)) on the last expression.
>
> Regards,
> Vagmi
>
>
> [1]: (
> http://blog.tarkalabs.com/2015/04/30/experience-report-introducing-an-experienced-ruby-developer-to-clojure/
> )
> and
>
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--
Ben Wolfson
"Human kind has used its intelligence to vary the flavour of drinks, which
may be sweet, aromatic, fermented or spirit-based. ... Family and social
life also offer numerous other occasions to consume drinks for pleasure."
[Larousse, "Drink" entry]
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