from https://github.com/rplevy/mostly-useful (not updated in a while)
(defn flip
"given a function, create a flipped 2-argument function"
[f]
(fn [a b] (f b a)))
(defmacro flop
"create a version of a function with a modified arity as specified by a
vector of zero-indexed positions, e.g. [0 3 1 2]"
[f positions]
(let [syms (vec (repeatedly (count positions) gensym))]
`(fn [~@syms] (~f ~@(map syms positions)))))
On Thu, Apr 30, 2015 at 5:49 PM, Jony Hudson <jonyepsi...@gmail.com> wrote:
> Another option is to use `as->`
> https://clojuredocs.org/clojure.core/as-%3E . It's more verbose ... I
> kind of like that aspect of it, but it may not be to everyone's taste.
>
>
> Jony
>
>
> On Friday, 1 May 2015 00:31:05 UTC+1, Vagmi Mudumbai 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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