Does anyone know the historical reason some returns true or nil instead of true or false? Is there a similar function that only returns a boolean value?

some is actually not going to return true all the time either

some returns the result of apply pred to the elements when it is truthy

user=> (some #{:fred} [:fred])
:fred
user=>

Oof

Thank you for clearing that up. What is the canonical way to test if any of the values in a collection (mainly a vector or list) match my pred?

some

some is there exists and every is for all

Ok, so I need to do my own conversion to bool if I want only a boolean?

if you really need booleans instead of truthy/falsey you can use (comp boolean some)

Thanks!

but most things in clojure (if, or, and, etc) are fine with nil and false as false and everything else as true

Oh, that's great to know. Thanks.

often the only times i care about true booleans is i’m grouping by a predicate and then i need true or false. (let [{missing false valid true} (group-by pred coll)] ...). Most other times truthy and nil punning are just fine

Ok, great. Thank you. I was worried that Clojure was stricter about the nil/false distinction.

I use the slf4j in deps.end

:deps{org.slf4j/slf4j-api {:mvn/version "1.7.36"}}

user=> (require '[clojure.tools.logging])
SLF4J: Failed to load class "org.slf4j.impl.StaticLoggerBinder".
SLF4J: Defaulting to no-operation (NOP) logger implementation
SLF4J: See  for further details.

@imxingquan You've specified the API (good) but you also need to specify an implementation: slf4j-simple is probably what you want. There's also slf4j-nop (for no logging) and several others (including bridges for other logging libraries)

(Java logging is a giant mess!)

This may help https://lambdaisland.com/blog/2020-06-12-logging-in-clojure-making-sense-of-the-mess (or it may confuse further). At work, we've decided to use log4j2 but that has its own peculiarities as far as getting it all set up with deps.edn etc.

user=> (log/info "hello")
[main] INFO user - hello

I add logback.xml to resources dir, but there's no log file in ~/log/taskphone dir

I use the project/jar, show error

$ clojure -X:project/jar :main-calss myapp.core
$ java -jar project.jar 
no main manifest attribute, in project.jar

(def seq1 [1 2 3 4 3 4])
  (let [col1 #{}]
    (doseq [x seq1]
      (conj col1 x))
    (println col1))

  ;; I want this result col1{1 2 3 4}
  ;; pseudocode
  var col1 = #{}
  for (n in seq1){
      if(n is not in col1){
          add n to col1                 
      }
  }

hi, I wonder how you spec functions. With simplified examples, I sometimes like to put valid? at the input and output of the function like below. But this approach may cause some degree of performance issue, if I use extensibly, right?

(defn add-seven [x]
   {:pre [(s/valid? int? x)]
    :post [(s/valid? int? %)]}
  (+ x 7))

(s/fdef add-eight
  :args (s/cat :x int?)
  :ret int?)
(defn add-eight [x]
  (+ x 8))

(require '[clojure.spec.test.alpha :as stest])
(stest/instrument `add-eight)

Hello, I am trying to implement auto-reconnect websocket logic (with fail safes so that i am reasonable user). I am using atoms to hold the websocket client object which i later use for reconnects. Sometimes i WS client might not even be created so i made a loop to attempt to create new connection and store it in atom. My question is will i create memory leak or will WS client objects be properly garbage collected if i (swap! connection assoc :socket (connect client url)) I realize that swap might be executed multiple times and that it should be used for pure functions but reconnect logic shouldn't happen often and i my thinking is if connections get garbage collected without being closed - all is well. If my whole approach is backwards would you mind sharing resources how this could be done properly? Thank you for your time

swap! potentially executing multiple times doesn't matter above. the final argument to swap!, the result of calling (connect …) is calculated only once.

You are calling swap with a pure function: assoc

If you are calling swap! in a loop, connecting multiple times, YMMV

Your clients/connections will be GCed when nothing hangs on to them. To prevent the map inside the atom from hanging on, when a connection breaks or closes, swap! dissoc it from the atom

Hello! When should I use defonce instead of def? Below is a code snippet taken from shadow-electron-starter repo. defonce is used. I’d like to know is def ok here? What’s the difference between defonce and def?

(defonce state (atom 0))

(defn root-component []
  [:div
   [:button
    {:on-click #(swap! state inc)}
    (str "Clicked " @state " times")]])

reloading the namespace will not recreate the state var

Let's say I have a string like "the quick brown fox" and I want to replace all the spaces with hyphens... how can I do this in clojure?

https://docs.oracle.com/javase/7/docs/api/java/lang/String.html#replaceAll(java.lang.String,%20java.lang.String)

there is a clojure.string namespace that wraps a lot of that stuff, but I tend to just call the methods on String

Ok. Is this better than using the "replace" function from clojure.core?

yes

I've never ever used clojure.core/replace

might as well just use clojure.core/map

(replace technically has some optimizations for vectors)

do you mean clojure.string/replace? b/c that has some nice affordances

well, neither replace I guess

(clojure.string/replace the-string " " "-") ?

but the replace in clojure.string is just because I habitually use the methods on String directly unless someone reminds me about clojure.string

the replace in clojure.core, I just use map for that kind of thing

in particular, the pattern/f-of-match arity can often be useful in clojure.string/replace

Ok thanks

What about if I want to delete certain characters from a string? Like if I want to turn "quick #brown !fox @ " into "quick-brown-fox" (I'm thinking about this in context of URLs)

replace with the empty string

Can I replace the characters with "" ? Or is there a better way to delete things? Thanks for the help guys

"better way" is extremely dependent, replacing with the empty string is likely to be good

How do I represent special characters? I'm thinking I will do (replace string "???" "")? What do I put for ???... do I put all the special characters I can think of, or is there a more succinct way?

depends what you mean by special characters

Anything that should not show up in a URL

there are unicode escapes and escape seequences for certain control characters

you could just use java's built url encoding and decoding

you can use a regex for grabbing multiple chars

https://docs.oracle.com/javase/7/docs/api/java/net/URLEncoder.html

but actually using a url-encode/decode is probably better for sure

Ok cool, I'll look more into that 🙂

Thank you

Ok a very beginner question... I found out that ring has a function ring.util.core/url-encode. I tried to use it in the repl with

(ring.util.codec/url-encode "this is my string")

Execution error (ClassNotFoundException) at java.net.URLClassLoader/findClass (URLClassLoader.java:433).
ring.util.codec

(require '[ring/ring-codec "1.2.0"])

Execution error (ClassCastException) at user/eval2107 (REPL:1).
class java.lang.Character cannot be cast to class clojure.lang.Named (java.lang.Character is in module java.base of loader 'bootstrap'; clojure.lang.Named is in unnamed module of loader 'bootstrap')

ring is a separate library

What's the correct way for me to require everything? 🙂

a library is a collection of code (clojure namespace, java classes, etc), when you launch you jvm process it needs all the libraries available at startup, so typically however you are launching that jvm process will need to be told what libraries you are using

you cannot require "everything"

[ring/ring-codec "1.2.0"]

a maven coordinate is one of many ways you might specify to whatever tool you use that starts a jvm what libraries is should have available

So why doesn't

(require '[ring/ring-codec "1.2.0"])

because require takes clojure namespaces, not maven coordinates

Ohhhh I see. How do I do the namespace?

and by the time you are calling require, you are in a running jvm

So do I need to add it to a project.clj file before just doing a repl out of the blue?

and the set of libraries available to that jvm is already set (not entirely true, but close enough)

yes

Ohhhhhhhhh ok. Thanks! I'll try to add it to project.clj and then try again 🙂

once you have added it to you project.clj, then that library will be available to use, but you'll need to use require to load namespaces out of that library

(added it to your project.clj and started a new repl)

Ok sweet thank you!