@lxsameer You will have a problem with middlewares that modify responses if you want to return deferreds from you handlers

anyone familiar with hcitool lescan?

Any recommendations on a Clojure library for Kafka integration?

@noisesmith thanks man

@yonatanel please do tell, So on top of my head you need to deref the response and generate a new one in middlewares right ?

it turns out I can't do (transient (list)), can I?

or is looping and consing over just (list) (need to prepend elements) good enough?

@misha you're right. transients exist because sometimes you don't need intermediate objects so you improve perf by not constructing them in case of a linked list, intermediate objects are part of the final structure, so basically there's nothing to improve

@leonoel makes sense, than you. do you happen to know which is faster/preferred from any pov: (list) or '()?

I doubt there is any difference at all

splendid

how can I have a spec that makes sure the value is a datetime? (a string with an iso formatted datetime value in it). With a regex or is there something better?

@leonoel btw you don't need to use '(), it accepts ()

true

I've got an exercise I can't figure up an elegant solution for: Let S be a sequence of sets. Compute R the sequence of sets such that each element of R is equal to the element of S at the same position, but also shares no elements with any sets that exist before that position in S.

@bcbradley so does this mean taking the subset of each set in the series that consists of the elements not seen in any of the sets so far?

@noisesmith yeah, almost-- "not seen in any of the sets so far (EXCEPT the current one)"

otherwise it would just be empty sets all the way

(defn f
  ([sets] (f sets #{}))
  ([sets seen]
   (when-let [[set & sets] (seq sets)]
     (cons (into #{} (remove seen) set)
           (lazy-seq (f sets (into seen set)))))))

thats a pretty nice way to do it

i wonder how others might try it, there seem to be bunches of ways; i've spent a lot of my free time recently just trying to come up with new ways xd

is it an elegance contest ?

yeah, but thats obviously subjective

it might also be interesting to have a performance contest

its just a fun problem tbh

sure !

+user=> (:acc (reduce (fn [{:keys [acc seen] :as state} s] (-> state (update :acc conj (set/difference s seen)) (update :seen into s))) {:acc [] :seen #{}} [#{1 2} #{2 3} #{1 2 4 5} #{1 4 5}]))
[#{1 2} #{3} #{4 5} #{}]

the lazy-seq version is nicer

yours isn't terrible though, its very concise! 🙂

hmm one could also whip up something using reductions: (map (fn [r seen] (set/difference r seen)) r (reductions into #{} r)) (untested)

transducer version :

(defn xf [rf]
  (let [seen (volatile! #{})]
    (fn
      ([] (rf))
      ([r] (rf r))
      ([r s]
       (let [xf (remove @seen)]
         (vswap! seen into s)
         (rf r (into #{} xf s)))))))

might as well show the prettier version of mine

+user=> (->> [#{1 2} #{2 3} #{1 2 4 5} #{1 4 5}]
             (reduce (fn [{:keys [acc seen] :as state} s]
                         (-> state
                             (update :acc conj (set/difference s seen))
                             (update :seen into s)))
                     {:acc [] :seen #{}})
             (:acc))
[#{1 2} #{3} #{4 5} #{}]

Clojuredocs question (I don't know whom to ask really): a number of pages appear to only work with clojure.data.xml but the examples use (or require) clojure.xml. The codes appears wrong on pages like this. Should this be edited or is it correct as-is? e.g. https://clojuredocs.org/clojure.zip/edit

i really like how short it is

dang that is the most elegant one yet

not the most efficient though

i feel like leonel's is probably the most efficient

well i take that back, maybe astro's is

I have a hunch astro’s would be if it used (into #{} (remove …) …) instead of remove / set

this was a really fun problem 🙂

lots of variety in solutions

it's actually the same solution as @the-kenny , once cleaned up

just figured out that set/union and set/difference don't leverage transients

yeah, I’d use into instead of set/union in 100% of cases

and actually into with a remove transducer can easily replace set/difference

(set/difference a b) becomes (into #{} (remove (partial contains? b)) a)

but doesn't reductions defeat the purpose of using transients in the set/union case?

I mean with reductions you can't efficiently use transients as every steps needs to be persisted

@bcbradley I think you meant your problem to state that “…each element of R contains all and only those elements of the lement of S at the same position which are not seen in any sets that exist before that position in S”? Otherwise e.g. in noisesmith’s solution example you should expect [#{1 2} #{2 3} #{1 2 4 5} #{1 4 5}] => [#{1 2}] since all sets of R must be equal to their respective positioned elements in S

@kingcode right - I read it that way at first but the problem statement didn’t seem coherent

so I made some assumptions

Thanks for confirming…I think all other solutions do the same?

your are right! yeah everyone assumed as you put it

yeah - they should all calculate the same way

@bcbradley I think this would be a nice candidate to http://4clojure.com

I’ll try my own code-golfing on that… 🙂

@kingcode i sent them a message on freenode

@bcbradley Great…hopefully they will respond. I did submit a “Towers of Hanoi” candidate months ago, but never saw it added, or heard from anyone.

My solution is similar to noisesmith: (fn [sets] (-> (fn [[r seen] s] [(conj r (clojure.set/difference s seen)), (into seen s)]) (reduce [[] #{}] sets) first))

@kingcode you can surround your code with ` (triple backtick) to get it to format properly

Haah, thanks @bcbradley!

Still new to slack…

How does one enter a new line without triggering a Send?

shift + enter

OK..thanks!

Sorry for the verbosity, making my code snippet pretti..er:

(fn [sets]
  (-> (fn [[r seen] s]
        [(conj r (clojure.set/difference s seen)),
         (into seen s)])
      (reduce [[] #{}] sets)
      first))

thats a very creative way to do it

i wouldn't have thought of that approach!

It’s not very compact/elegant, but probably fast enough…am studying others’ and learning.

Great problem, thanks for sharing - what name did you give it on http://4clojure.com? I will watch for it…

I didn't think to give it a name, I just described the problem and example input and output data in a message on freenode

clojure is so compact and elegant as a language there are probably hundreds of ways to solve even a problem the average solution length of which 8 lines; i think there is a ton to learn from simple problems like that one, regardless of whether you are super new to clojure or super experienced with it

for instance, drowsy's approach involves a fairly novel use of reductions with sets that i haven't seen before

aw OK….you might want to register/login and to the “Submit a problem” tab on http://4clojure.com itself..

oh sorry i didn't see that xd i'll do that now

Yes indeed, problems in the small is a fantastic way to improve….thanks!

Indeed, wasn’t aware of reductions myself, will check it out 🙂

hrm i don't see that tab

Once logged in, you should see two navigation rows at the top. The second row should have ‘Account Settings’, ‘Leagues’, and ‘Submit a Problem’..

not for me, but you are free to submit the problem if you'd like (or anyone else, you don't have to bother giving me credit-- name it whatever you want :d)

what’s the correct way to place a async/dropping-buffer in a async/pub and a bunch of async/subs?

quick Q: How can one build vars in a macro? I have a spec that I want to turn into a symbol within a macro (e.g.: (defaction ::some-spec ..) should result in a function (defn make-some-spec ..) but not sure how to go about constructing the make-some-spec symbol

... it's always when you finally type something out that you figure out the solution.. nevermind >.<

@dadair haha - (comp symbol name) is an elegant choice

yep that was a quick "doh" moment

err, I guess you need to use str in there too

I do know that if I place a dropping-buffer in all three places, I get a NoSuchElementException internally in core.async

@csm put it on b, that way either a or c (or both) could be passed in by the code creating it

which is a nice pattern, it lets consumers decide what transducers should be on a channel, etc. or how much buffering they need based on activity patterns

b, the one in the middle, is the one that code would always own, so it’s the sensible place for things it specifically should define

the use-case is to partition a stream by a key, then to further partition/batch items via a transducer per sub

using the same buffer in multiple channels is a bad idea

ooohhhh..

the constantly was totally wrong, I get it

I definitely make that mistake a lot, thinking the body is evaluated each time

@bcbradley strange…perhaps you just need to submit a few exercises ‘ solutions? I’d be happy to submit it for you if you prefer.

you can submit it if you'd like

OK…will do and give you credit whenever possible 🙂

(every? keyword? [])
=> true

Hey, can't believe I haven't hit this before, is there something like swap!, except that it can return an extra value?

like, [new-state other-value]... Or would I have to build that with compare-and-set!?

you can write it yourself using compare-and-set!

heh, yup

there’s also using refs and returning the relevant data from your transaction

since caring about two values at once can be a sign that the values should be coordinated and that’s what refs are for

This was working two weeks ago, breaks today when I launch CIDER from within the project.

error in process sentinel: Could not start nREPL server: Could not find artifact org.clojure:clojure.math.numeric-tower:jar:0.0.4 in central ()

Could not find artifact org.clojure:clojure.math.numeric-tower:jar:0.0.4 in clojars ()

This could be due to a typo in :dependencies or network issues.

If you are behind a proxy, try setting the ’http_proxy’ environment variable.

are you sure there isn’t a hidden typo? https://mvnrepository.com/artifact/org.clojure/math.numeric-tower - maven claims that 0.0.4 is available

(there is a typo)

oh yeah - there’s one too many clojures in there

[org.clojure/clojure.math.numeric-tower "0.0.4"]

remove the second “clojure”

https://github.com/clojure/math.numeric-tower#releases-and-dependency-information

Better, thanks!

I'm trying to make a lib out of a "predicates by example" functionality I regulary use. So any feedback is welcome: https://github.com/IamDrowsy/ebenbild/

i like that it does one thing and only one thing

a lot of libraries could learn a thing or two from that

I tried to keep it simple.

It's a bit opinionated as for example a String matches on inclusion.

And I thought about some extensions mechanisms, but settled with the opinions I need, as it's much simpler and you could always fallback to plain fns