in cider, how can I reset the repl ?

@steiner3044 What do you mean by "reset"? (there's a #cider channel for deep dives on that)

reset all the variable and namespace, then restart

here in my src/book_clj, there is three file

➜  book_clj ls
book.clj  core.clj  server.clj

(ns book-clj.core
  (:require [book-clj.server :as server])
  (:require [book-clj.book :as book]))

Hi guys, how do I tread my output in this such that I can use the apply str to join a resulting list of strings?

(defn sing
  "Given a start and an optional end, returns all verses in this interval. If
  end is not given, the whole song from start is sung."
  ([start] (sing start 0))
  ([start end] (for [v (range start (- end 1) -1)]
                 (apply str (verse v)))))

Ohhhhhh I got it I need to put (apply str to wrap the for

@zackteo Using clojure.string/join is probably more efficient than apply str (and I'd say more idiomatic).

You can also provide a separator: (clojure.string/join ", " ...) to provide a comma-separated list.

@seancorfield yeap i realised after looking at other solutions. I wanted to do (apply str ( interpose . Which I realise string/join does the same! Thanks tho :)

Hi - I'm trying to follow https://grison.me/2020/04/04/starting-with-clojure/ - but when I run jack-in (just choose leinigen option) - it fails with "could not parse project.clj"

@kl Sounds like your project.clj file is not valid -- can you share it here?

That article doesn't seem to talk about project.clj -- the only mention seems to be in an error message when the formatter is run?

Since it talks about CLI / deps.edn, I'm a bit surprised it suggests "jack-in" since that's often associated with Leiningen which the article doesn't talk about setting up a Leiningen project at all...

...it seems like a very confusing article to me, to be honest.

its the one http://clojure.org links to for beginners

😞

any better one for explaining how to startup - using an existing project with vscode+calva? 🙂

The code works for everyone else (who'se typicly using emacs)

I usually use vim - but figured between intellij and vscode (the 2 covered in the article - vscode would be fine - so I installed codium build)

So if I have a directory starter and within that directory two files: deps.edn and playground.clj, with the following content: deps.edn

{:paths ["resources" "src"]
 :deps {org.clojure/clojure {:mvn/version "1.10.1"}}}

(ns playground)

(+ 40 2)

Then with starter opened in VS Code, I choose jack-in. It gives me a menu of project types to choose from. I choose Clojure CLI. Then with the playground.clj file opened, I choose to load it. Calva: Load current file and dependecises. Then I can evaluate the (+ 40 2) form. With the cursor inside it, I press alt+enter.

If you do these steps. What happens?

hey, how can I write a data into a binary file, and then read it as binary data? in other way, how to serialize a data?

Is there an elegant way to dispatch within a function to an inline multi-function? Sorry that's confusing. What I want to do is the following:

(defmethod foo :some-key [& params]
  (dispatch params
    ([] ... );; handle empty params 
    ([a] ... ) ;; handle single arg, binding it to a
    ([a b] ...) ;; handle binary cases, binding them to a and b
     ...))

(defmethod foo :some-key [& params]
  (apply (fn 
           ([] ... );; handle empty params 
           ([a] ... ) ;; handle single arg, binding it to a
           ([a b] ...) ;; handle binary cases, binding them to a and b
           ...) 
    params)))

Is there a recommended library for wrapping common math functions and constants (trig functions, pi, etc) for use in cljc files ?

Is there a better way to do this idiom which I have found myself doing several times in the past days?

(map (fn [_] operand) (range n))

take a look at repeatedly

@jimka.issy seems like a rather complicated way to do (repeat n operand)

great. Thanks @jason358, For some reason I had convinced myself that repeat only worked for strings, and did n-many string concatenations.

When starting a repl using clj is there a way to break a long running evaluation using some keyboard shortcut?

My googling hasn’t found anything obvious, so I assume there isn’t…

Ctrl-C?

there isn't a way to break long running evaluation

some evaluation environments like CIDER/NREPL stop threads preemptively using java's Thread.stop(), which has been deprecated for decades

the official way to do stop something on the JVM is to use Thread.interrupt(), but that is cooperative with the running code

(need to check the interrupted flag, or use an API that respects it)

but, TLDR, no, nothing generic. If you eval something like (loop [] (recur)) it's going to do that forever

you could try https://clojure.github.io/clojure/clojure.repl-api.html#clojure.repl/set-break-handler!

can't say I've tried that in a long while but seems like it doesn't work anymore :)

I'd like to except one domain for cors (cross-origin CSRF) ... I'm trying to put the flags :access-control-allow-origin [#""] and :access-control-allow-methods [:post] on (wrap-cors ...) but it's not working...

still "invalid anti forgery token"

@sova CORS and CSRF are different things. That error is not coming from CORS and you won't fix it by changing your CORS configuration. It means the submitting form does not contain the appropriate hidden field.

Can anyone help with using namespace keywords as enums? I have a namespace and was thinking to use keywords as possible statuses of an operation. There is an option to use namespace keywords. But i want "status" to be a qualifier too. For eg, if my namespace was my-app.ops , I plan to have possible status as :my-app.ops.status/status-1 , :my-app.ops.status/status-2 . This was possible if i had a separate namespace as my-app.ops.status, but i don't have one such. Does anyone have any opinion as how to proceed?

you can just use those keywords - keyword qualifiers don't have to refer to an existing namespace

user=> :i.made.this/up
:i.made.this/up

Yes, agree to that. I was looking for a way to leverage :: (something like ::status/status-1)

you can't use :: unless you have an alias, which must refer to an actual namespace

you can kind of hack it by calling create-ns then alias but I find it's easier to just use the full kw name

Random noob question: how can I turn an int into a sequence of digits? If I were in Python I could cast a int to a string and iterate thru each character, parsing it as an int. Is there a way to do this in clojure? Context: a programming puzzle. Ppl rarely need to doo this normally 😄

str will make a string from an int

and strings are treated as sequences of characters by the seq fns

@seancorfield is CORS a drop-in replacement for anti-forgery?

(map #(Character/digit % 10) (str 123))

a 3rd-party API is hitting my server, there is no potential for a CSRF token ..I just have to whitelist one endpoint but it's not clear. seems like CORS would be the whitelisting for certain domains... still important to have anti forgery?

I usually do something like this -- (reverse (map #(mod % 10) (take-while pos? (iterate #(quot % 10) 12034)))) (no comment on efficiency or completeness, but worked well for me for advent-of-code)

@sova, i think that particular endpoint shouldn't be wrapped with csrf then. Instead, some other authentication mechanism can be used

so far i agree 100% 😃

but i'm not sure how to split my routes with run-server

I am bumping into a rather puzzling error. I am trying to run a docker-compose command via clojure.java.shell to set up an admin user in a docker container automatically. If I run the following from Rich comment block, it works fine.

(sh/with-sh-env {"COMPOSE_INTERACTIVE_NO_CLI" 1}
    (sh/sh "docker-compose" "exec" "-T" "portal" "htpasswd" "-bc" "/etc/nginx/unryo/htpasswd" "admin" "a"))

(let [cmds [["docker-compose" "pull"]
            ["docker-compose" "up" "-d"]
            ["docker-compose" "exec" "-T" "portal" "htpasswd" "-bc" "/etc/nginx/unryo/htpasswd" portal-username portal-password]]]
  (doseq [cmd cmds]
    (println cmd)
    (sh/with-sh-env {"COMPOSE_INTERACTIVE_NO_CLI" 1}
      (println (apply sh/sh cmd)))))

(def application-routes 
  (routes 
  #'service-routes 
  (wrap-routes #'userland-routes wrap-anti-forgery)))

Hi I am trying to understand how I can use lazy sequences. I am writing a sudoku generator, where I generate 9 random rows at a time, I hope to filter according to some properties and then take the first nine valid rows as my sudoku grid. However I get eval timed out after few seconds, maybe lazy sequences are not meant for this problem?

who times out?

(defn sudoku-grid []
  (->> (repeatedly nine-valid-rows)
       (filter valid-columns?)
       (filter valid-blocks?)
       first))

I am actually running figwheel

Is there a difference between lazy-seqs in clojure and clojurescript?

is it possible you never generate versions with valid-columns or valid blocks?

if you aren't probing your search space well you could either be enumerating quite a few bad apples or even never getting into a valid grid

this could be a simple algorithmic complexity question - if your guesses are naiive enough, you could run out of time before finding anything useful

you could work out how many random guesses it would take to guess a valid sudoku, then see if there's anything about your guessing that could be informed by past results, or rule out whole subtrees of the problem that aren't worth trying

lazy-seqs are slower than the equivalent loop, but only by a constant factor, so they won't be the source of this problem

you could try adding (take 10000) between the repeatedly and the filters

that should return very fast

and likely establish that your first 10k guesses were all wrong

So...I'm having trouble understanding a peculiar bit of code I wrote

I'm trying to implement a REPL-driven workflow in the browser (cljs + shadow) by mounting components on a div

(I know DevCards exists, but I kind of wanted to figure this out on my own)

Anyway, long story short, I wrote mount so I can call it in the REPL:

(defn playground-dom [] (.getElementById js/document "playground"))

(defn mount 
  ([element]
   (d/render [element] (playground-dom)))
  ([head & elements]
   (let [node (reduce #(conj %1 (%2)) [:div (head)] (vec elements))
         f    (fn [] node)]
    (d/render [f] (playground-dom))
     )))

My question is, why does this multi-arity definition work but this one gives me a not ISeqable error?

(defn mount 
  ([element]
   (d/render [element] (playground-dom)))
  ([& elements] ;; I removed the head!
   (let [node (reduce #(conj %1 (%2)) [:div] (vec elements))
         f    (fn [] node)]
    (d/render [f] (playground-dom))
     )))

REPL messages:

> (defn x [] [:p "try"])
#'clojure-playground.core/x
> (mount x x x)
#object[Error Error: function clojure_playground$core$x(){
return new cljs.core.PersistentVector(null, 2, 5, cljs.core.PersistentVector.EMPTY_NODE, [new cljs.core.Keyword(null,"p","p",151049309),"try"], null);
} is not ISeqable]

You did not remove the head

Sorry, I guess you did, I didn't realize that comment was referring to the earlier version

The error there is that varargs and fixed args can only overlap at 0

(or 0 varargs I should say)

Basically you can't have arity overlap between varargs and not varargs

Why you are getting that terrible error message I dunno

Ahhhh that makes sense

I guess I could remove the 1-arity definition and make it fully general

Hi guys. I have a project generated by lein new reagent <app_name> . I’ve made an API call in the backend and have a handler to parse the resulting JSON.

(defn get-cards [req]
  (let [resp @(client/get "" options)]
    (if (= 200 (:status resp))
      (def cards-object (json/read-value (:body resp) (json/object-mapper {:decode-key-fn true}))))))

@njerigachoka hello! First of all, consider def as a const in js.. so you never want to use it in instances like that one. Instead, you want to directly swap your reagent atom and store the result of the handler in there. In other words you want to def somewhere in your code an atom, being (def state (reagent.core/atom nil))

Then in your handler you do: (reset! state (json/....))

And in your UI component you do @state to get the values out of it

If this sounds a bit unclear, I can paste a more comprehensive example.

Yeah, this is a bit unclear. I’d appreciate the example.

check out "Managing state in Reagent" https://reagent-project.github.io/ it should be very similar to that

Writing it know 🙂

This should be clear enough @njerigachoka :

;; This is your function that I assume you want to call on-mount (or from an on-click handler)
(defn get-cards [req state]
  (let [resp @(client/get "" options)]
    (swap! state assoc :http-response
           (if (= 200 (:status resp))
             (json/read-value (:body resp) (json/object-mapper {:decode-key-fn true}))
             "Something went wrong!!"))))

(defn main-panel
  (let [;; This is a reagent atom. Every time a value in here changes, the views that
        ;; use it will re-render automatically (that's the react bit of it).  Usually,
        ;; you want to store your data in a map with several keys, which looks similar
        ;; to a JSON object.
        state (reagent.core/atom {:other-state-stuff "other stuff"
                                  :http-response nil})]
    ;; Anything happening before the (fn []...) function will fire only once, so this
    ;; space is great for your on-mount logic.

    ;; pass state to your function along with your other params
    (get-cards req state)
    (fn []
      [:div
       [:h1 "This is your UI component!"]
       [:p "To print the state values use @"]
       [:p (get @state :other-state-stuff)]
       ;; when nil, nothing will show in the UI
       [:p (get @state :http-response)]
       [:h3 "this is h3"]
       [:p "this is p"]])))

Thanks, this makes more sense. What does calling “on-mount” mean? (Sorry, I’m a real beginner 😅)

Ah, that was a quick search away. Nevermind. Thanks again, @lucio

Glad you got there 🙂 No problem! @njerigachoka

btw thanks @hiredman kinda got distracted there for a sec

this community is awesome

What is the state of http-kit? Is it production ready? I am seeing ptaoussanis has been maintaining it.

it's not broken, I don't think http-kit or aleph are in active development

if you use ring you can trivially swap out http-kit, aleph, or jetty

@lpan For what it's worth, we use Jetty very heavily in production (driving 40+ dating websites with a global customer base).

We swapped to http-kit at one point (due to a weird thread death bug in Jetty that later got fixed) but New Relic doesn't support http-kit so we swapped back to Jetty.

I am building an app that might handle potentially thousands of concurrent websocket connections. I thought maybe I should start with an nio-based HTTP server 😜

We have a real-time chat server based on Netty directly, using Java interop, that's all based on concurrent websockets. My colleague knows more about it than I do tho'...