Is there a built-in function like every? that instead of returning false when the predicate fails returns the item in the collection ?

I'll cook my own

hmm, take-while my ease it

so I'm working through 4Clojure at the moment, and am starting to wonder which is the best way as far as readability vs performance vs <insert whatever else here>.... obviously there is a bunch of ways to do the same thing.... but I'm not sure which ways are overall better (used a bit loosely here)? For instance, on the duplicate a sequence problem.... My solution is #(reduce (fn [res el] (into res [el el])) [] %)

@lockdown- You could try some but with the complement predicate.

but there are so many others like #(interleave % %) and (mapcat #(list % %))

you can replace (fn [res el] (into res [el el])) with (fn [res el] (conj res el el))

I feel like I'm about to embark down a rabbit hole haha....

the mapcat one doesn't work quite like that (that's an uncalled transducer) but is likely the most straightforward solution

i think using repeat instead of list conveys the intent better

@noisesmith I am assuming conj is better here because I am just adding to the end of the vector? ... would into be better if I was using a list or a map data structure?

into is a reduce that calls conj

so using conj directly is simpler

ah... gotcha... thx!

and into is better if you are eagerly filling one collection from another (with optional transformation as you consume the items)

as in going from a list to a set for example?

here's a version using into properly (won't work on 4clojure's clojure version) (into [] (mapcat (fn [e] [e e])) coll)

or for combining two collections, or altering a collection as you use it to fill a specific collection type

that mapcat doesn't get used on the collection, it's a transducer that into uses instead

I'll have to stare at that awhile lol

+user=> (def m (mapcat (fn [e] [e e])))
#'user/m
+user=> (into [] m [1 2 3 4])
[1 1 2 2 3 3 4 4]

when you don't give mapcat a collection, it returns a transducing function. when you provide an extra arg to into before the last arg, it uses it as a transducing function to transform its input

I'm getting how it is working.. I'm not getting how it is a correct use of into since I am guessing I am at a point where I am not sure what is correct when/where when it comes to Clojure

I could rephrase that - it's a case where into is better than alternatives

your usage of into inside reduce was just an obfuscated conj

or more simply, don't create a collection just to pass it as the last arg to into, there's always a better alternative

ah.. I see what you're saying... I'll have to think that through a bit when I'm working through problems... but that makes sense

the reasons to use into with a mapcat transducer instead of mapcat directly are in case you know you are using the data eagerly and want better performance, or if it clarifies / simplifies code to be able to describe the transducing function separately from the rest

in clojure's speak is a map refer as a collection too?

map the function and map the collection are two different things

we can disambiguate by calling the collection a hashmap

ok, was referring to map the data structure

both describe something related to mapping from items of one domain from items to another, and for historical reasons they both get called "map"

and they both can be used as functions... so that's fun

into is frequently used with hash-maps because the basic collection operations mostly return lazy-seqs, and into is an easy way to get a hash-map back

for example, in Java, maps are not part of the collection interface, it has its own

that's true in clojure as well

+user=> (instance? java.util.Collection (java.util.HashMap.))
false
+user=> (instance? java.util.Collection {})
false
+user=> (instance? java.util.Map {})
true

but java "Collection" is overly specific, basic cs tells us that hash-maps and queues and trees are all collections

got it, was wondering how it was used in clojure "speak" 😉 cause of java

+user=> (coll? {})
true

coll? gets a little closer to our idea of what a "collection" is, but only for clojurey things sadly

+user=> (coll? (java.util.HashMap.))
false

nice, I need to look more at the cheatsheet

re your into hash-maps, the same applies for vectors no?

sure, or sets etc.

And re: @sundarj’s comment about using repeat to clarify the intent:

(into [] (mapcat (partial repeat 2)) [1 2 3 4])

or

(into [] (mapcat #(repeat 2 %)) [1 2 3 4])

(and I agree that expresses the intent better than (fn [e] [e e]) in my opinion)

I like (fn [e] [e e]) more, but what do I know?

Eh, I like both for different reasons. logs off

I don't know which would be considered more idiomatic. My preference is entirely subject. Another option would be #(vector % %) which some people may prefer.

crazy how many ways there truly are to do something.. still trying to wrap my head around that.... I feel that Haskell had a more clear path to solutions (trying to at least compare functional languages here even though they really are way too different to compare)

If I'm calling a function and would like to conj two values from the result of that function into a map, then return it, what's the best way to do that?

should i use a let to reference the return value, then do two conj's ?

@scott.archer If you're using clj-http you could have it parse the JSON response automatically, so you'd get back a hash map with keywords as keys -- that would make your code easier.

As it above, you could add a new binding in the let:

body (parse-string (:body response))

Instead conj, I'd probably use assoc:

(assoc my-site-info :token  (body "access_token") :ttl (body "expires_in"))

(assuming the additional let binding above)

@seancorfield Thanks, I caught the two calls to parse-string. I am using clj-http, so I'll see about having it parse the JSON.

I also find it's easier, with clj-http, to specify :throw-exceptions false and check the :status in the result rather than letting it throw.

Thanks again, i'm new and muddling my way through it. I'm decent at getting stuff working, but I want to learn the right way to do things.

Learning all the idioms takes the longest time. I've been doing Clojure in production for seven years now and I'm learning new stuff all the time!

Hi, I am getting null pointer exception. Can anybody explain why?

(loop [a 0]
  ((println "*** Sales Menu ***")
  (println "------------------")
  (inc a))
  (if (= a 0)
    (recur a)))

@kushalkanungo1991 Also, you are evaluating (inc a) but essentially throwing the value away. Perhaps if you explain what you're trying to do, maybe we can help guide you to a functional solution?

I am just trying to make an infinite loop and break it on a condition. I saw this example

(loop [accum []
       i     1]
  (if (= i 10)
    accum
    (recur (conj accum i)
           (inc i))))
;; ⇒ [1 2 3 4 5 6 7 8 9]

Hi is there a way to destruct the sequence in place sth like (hash-map (desctruct vec1) (destruct vec2))?

@kwcharllie379 https://clojuredocs.org/clojure.core/destructure check this out

@deleter Thanks! 🙂

Hey, I am in a project with Clojure and ClojureScript. I am running lein, Emacs, Cider and Weasel (Browser-connected ClojureScript REPL) on a GNU/Linux system. I am trying to wrap my head around how Cider is working in this environment and how to use the 2 REPLs. When i navigate to the project in Emacs and use M-x cider-jack-in-clojurescript it starts a new process on the system: clojure.main -m leiningen.core.main update-in :dependencies conj [org.clojure/tools.nrepl "0.2.13" :exclusions [org.clojure/clojure]] -- update-in :plugins conj [cider/cider-nrepl "0.17.0"] -- repl :headless :host :: and gives me 2 buffers that's connected to REPLs. But i dont know if on or the other is connected to a ClojureScript REPL or a Clojure REPL. How can i know? If I eval a sexp from a file buffer, how can i know to what REPL the sexp is sent?

Are there any examples of component and compjure? I’m not sure how to structure my app with stateful components. In C# my IOC container would just inject everything automatically.

@grierson Perhaps this section in the component readme helps? https://github.com/stuartsierra/component#web-applications should be pretty close to how it's done in compojure

@curlyfry would the ‘app’ be a map with keys for database, email, and other stateful components? Then just (:database component) inside my handler?

I actually don't use Component (I prefer Integrant, which has pretty much the same use case but works a bit different) 🙂 But the 'app' is called a 'system' in component, and is a map from keywords labeling the components to instances of components https://github.com/stuartsierra/component#systems

My advice is to study the readme, it's quite extensive!

I'm not entirely sure, better if someone who actually knows Component takes over!

Or the readme 😉

@jherrlin Did you try doing cider-repl-set-ns from the file in question? You can see the prompt change so you will know which repl will do the work. As far as I can tell it's just a simple case of anything from a .cljs file goes to the clojurescript repl and anything from a clj file goes to the clojure repl. I don't know the full details, but in my limited experience it works like that.

@soulflyer havent seen cider-repl-set-ns but will look into that! Thx! 🙂

hi guys i am trying to simulate movement on google maps of multiple entities in parallel i do this by having this

(defn start-mockup
  "travel time has minimal of 30 sec and max of 151 per bus-stop
  1 sec = 1000"
  []
  (let [root (io/file "resources/routes")
        files (rest (file-seq root))
        _ (println "Num. files: "(count files))]
    (doseq [file files]
      (let [data (read-string (slurp file))]
        (future
          (doseq [c (:coords data)]
            (let [travel-time (int (* 100000 (+ 0.03 (rand 0.121))))
                  _ (println "travel-time:" (int (/ travel-time 1000)) " sec")]
              (println "name" (:name data) ", coords: " c)
              (Thread/sleep travel-time)
              (client/post  ""
                            {:body
                             (json/generate-string
                              {:bus-line (:name data)
                               :current-lat (:lat c)
                               :current-long (:long c)})}))))))))

Can anyone point me to a "production" example of using clj-http to consume a REST API?

I've got mine working, but I'd like to see what robust error handling looks like in a real implementation.

on line 9 you put a vector in parens

forgot the quote heh

that means you are calling it

facepalms

you don't even need parens there, you can use []

is the result of another fn, a seq of vectors

then call seq on it

but reduce does that already

I wish examples would stop using '(...) because it's pretty much always worse than using []

ok, what I meant is that the coll passed to reduce is a seq of vectors from a function call

but noted

right, but if you need to emulate it being a seq, you can call seq on a vector

seen results as seqs sometimes confuses me with lists

but that is pretty much never needed (eg. reduce calls seq on its vector arg anyway)

a list is a kind of seq, but clojure functions that take seqs can turn a lot of things into seqs

so I think I'm getting a list but its a seq and run a test with a list with not quote 😉

yeah better to user more [] or call seq

my point is, to test something that takes a sequential collection, use a vector literal

right

but is there anything really wrong with '(1 2 3) ?

it's error prone in a way that [1 2 3] is not

you could forget the ', or try to put forms in that should be evaluated

and the set of places where '(1 2 3) is right and [1 2 3] is wrong are very small, and fixable by a call to seq

reduce hard lesson of the day, make sure the result of the first iteration can be used in subsequent iteraions 😉

I want to read a string from the user, it has some numbers and some strings, I'd like to use edn reader, any pointers?

i need to pass a java File object to some constructor. everything works fine when i execute my uberjar locally: (io/file (io/resource "mykey.pem")) where the file is in /resources/mykey.pem, but when i deploy the uberjar to AWS ECS i get an exception saying mykey.pem is not a file or directory. i get closer if i use io/input-stream and can slurp the contents once deployed.. but is it possible to convert a buffered input steam to a File object?

@joshkh so you need to include an additional file when packing an uberjar? it has been a long time since i did this ... let me do some research

thanks, sova. the thing is the file is definitely in the jar. i've extracted it and looked. so it's more of a problem with getting a File handle on it.

https://stackoverflow.com/questions/20389255/reading-a-resource-file-from-within-jar

do you need (io/file) ?

maybe you can use just io/resource

i definitely need a File object. (io/input-stream "mykey.pem") returns a valid BufferedInputStream

but the constructor of this java class expects a File. my lack of java skills are showing. 😉

(io/resource) works as well. it returns a URL.

Well, i just read this: If you need to slurp a file from a JAR file, don't call io/file on the result of calling io/resource, or you will get an exception that says the resource is "not a file". Instead, call slurp directly on the result of io/resource.

yup! saw that too! but slurp reads it into a string.

Aha, there is also If you need to copy a binary file from a running JAR (or WAR), don't call slurp as it will try and decode the file. Instead, extract similarily to:

(with-open [in (io/input-stream (io/resource "file.dat"))] ;; resources/file.dat
    (io/copy in (io/file "/path/to/extract/file.dat"))))

oh, nice one! i'll give it a go.

@sova thanks. that did the trick!

Hi everyone, Is somebody can help me here with instrumenting with deftype. All detail are here : https://stackoverflow.com/questions/50572207/clojure-how-to-instrument-another-protocol-in-implementation

@sova Re: edn/read-string -- is the problem there you have a string like "42 \"hello\" \"world\" 13" and you want to read all those expressions, not just the first one?

You could try (edn/read-string (str "[" user-string "]")) to get a vector of the expressions...

hi, I'm going to present clj(s) to my boss and colleagues this week and am currently thinking of the best way to demo how and why a REPL is a great tool to give fast feedback while building production ready code. any good ideas for code snippets?

I'd stick to the usual notepad, but i thought mb you guys come up with something presentable in even less time

@klaus.azesberger For me its always mind blowing how easy it is to implement a search field with re-frame. You could show a table and the have some input that you use to filter the table. Its just a few lines of code and can be live coded, if it is prepared well.

thanks, that certainly fits my time slot 🙂

i could use some of our real ansible configuration data by parsing the yaml files

I wish you good luck 🙂

i want to remove entries from sets in a nested atom.

(swap! lookup-rc update-in [:tags (keyword tag)] (remove entry-id) is not doing the trick.

for one thing remove doesn't return a set, but also calling remove like that will fail

Hmm, I thought it was like filter

if they are sets, (swap! lookup-rc update-in [:tags (keyword tag)] disj entry-id)

filter also wouldn't work in that context

update-in passes the object as the first arg, (remove entry-id) doesn't return something that can operate on a set

it returns a transducer which can't do much without a transducing context (update-in doesn't provide one of those)

okay, very cool. beginning to grok.

also, if entry-id is the actual id, that's not how filter and remove work, if it's a function that returns true for that id, it's weirdly named and it won't work with disj

what if i want to remove a keyworded map from an atom completely? can I do something like (swap! lookup-ab update [:entry-ids] disj entry-id) ? in an effort to remove something like the Set associated with 12 from :entry-ids { 12 #{1 2 3 4 5}, 13 #{1 2 3 4 5 6} }

that calls for dissoc, but otherwise yes

disj is for sets, dissoc for hash-maps

Cool.

aha. thank you. Where does remove come into play? disj did not show up in my elementary searching

remove is when you have a function that returns truthy for items that should be removed, and want a lazy-seq back

for now you can treat (remove f) as an error that doesn't complain (later you might care about transducers and learn about it)

+user=> (remove even? (range 10))
(1 3 5 7 9)

what you did:

+user=> (remove even?)
#object[clojure.core$filter$fn__5610 0x48e92c5c "[email protected]"]
+user=> ((remove even?) (range 10))
#object[clojure.core$filter$fn__5610$fn__5611 0x3d1848cc "[email protected]"]

it returns another transducer (one that would blow up if you ever tried to use it correctly as a transducer)

aha, fn / fn

filter / fn is cool and groovy but filter / fn / fn is not.

that's not what is happening here

you called remove with one arg, which returns a transducer

oh, because it doesn't know what dataset to apply this to?

calling a transducer with one arg (in this case your set) returns a broken transducer that doesn't blow up until you try to use it

it creates an invalid transducer, it's just nonsense but nonsense that clojure doesn't proactively check for

I should clarify - you can call a transducer with one arg - that is part of how they are used in transducing contexts, but that's not what's happening correctly here

but you don't need to know any of that- just treat (remove f) as a garbage in garbage out error until you know you need it

okay, thanks 😃

@seancorfield how would i access independent elements of a vector by index when I don't know how many there may be in total?

because when a user inputs tags, there may be many or few. i'm wondering if there is an idiom-esque way for how to iterate over strings in a vector of variable length

Ah, maybe just (doseq [x (rest (rest data))] ...) will be just fine 😃

thanks a lot

i'm catching some errors and printing out to the console when they happen, but i always also end up println'ing a nil

@sova once you have your vector, count will tell you how many elements are in it.

(a vector is always a finite number of elements and count is O(1) on it because vectors are Counted collections, as I recall)