Hello guys. I am very new in Clojure yet and am now reading Clojure for The Brave and True. I am thinking to read the entirely book first and them start coding for real. Do you think this is a good aproach? How was your process of learning Clojure? I would appreciate some help to speed up my study. I came from Java and have already some contact with functional programming in Javascript.

I would work as you go. I find that typing and thinking at the repl helps cement the concepts

Hello, can anyone recommend me some good books for learning clojure? As well as an additional book for learning web development with clojure?

I am currently reading the Joy of Clojure and it's good!

@db0349It's a bit dated but most everything is still true, and the second edition was made in 2016 I believe

But it goes fast, so maybe not a book for total beginner

Okay thank you! Does anyone have any recommendations for a clojure book for web development as well?

And that's fine I've done clojure in the past, and I just need to be refreshed

I believe http://www.allitebooks.in/web-development-clojure-2nd-edition/ was recommended to me, but I never read it

maybe someone else can comment on it

Okay thank you

🙂

👍

The second edition of Joy Of Clojure is from 2014, but from my understanding clojure hasnt changed a whole lot since then, right?

pretty much any book ever written about Clojure is still valid. I'm not aware of any glaring deprecations

new features have been layered on but not much has broke with the past

@db0349 The main thing to watch out for in older books is library versions. In particular, the older "monolithic Contrib" (1.2) isn't compatible with newer versions of Clojure, and several of the library names changed. But as long as your book is Clojure 1.3 or later, you're mostly alright /cc @john

@seancorfield thanks sean, nice to know!

Hi everyone! Quick question about using a library created in clojure in a Java project. What I did - I created a library in Clojure and I exported it using lein uberjar. - I took the (non-standalone) .jar and added it to my class path in my Java Project. How can I access the functions from that library in my Java project? What would be the import? Something like import project-name.core? Thanks a bunch!

-'s in clojure namespaces become _'s

but whether there is a class to import depends on whether you did aot, gen-class, etc

you can also use the java API for invoking Clojure (http://clojure.github.io/clojure/javadoc/)

http://clojure.github.io/clojure/javadoc/clojure/java/api/Clojure.html

Can clojure immutable data structure be used in java like java native data structure? I mean not by the java API for invoking clojure?

@tjh.xbow Technically yes, they implement the appropriate java interfaces (vector implements List etc.), but they might not be the most convenient option. https://github.com/clojure/clojure/blob/master/src/jvm/clojure/lang/PersistentVector.java

Howdy Y'all! I'm building a simple compojure + reagent app and I want to use the same compojure service but have it talk to multiple databases. Where should i store the configuration?

How do people usually abstract out effects in Clojure? Similar to how Haskell would use type classes or object oriented code would use interfaces

Multimethods?

Hello guys.

I am startin to learn clojure as a part of my master studies course.

I've started with book Clojure for the brave and true

I've created application with leiningen, and I was wondering why this code thorws exception, but prints value before it.

(ns clojure101.core
  (:gen-class))

(defn -main
  "I don't do a whole lot ... yet."
  [& args]
  ((def greting "Hello there")
   (println greting)))

and here is the output.

Hello there
Exception in thread "main" java.lang.ClassCastException: java.lang.String cannot be cast to clojure.lang.IFn, compiling:(/tmp/form-init7051855349601256406.clj:1:73)
	at clojure.lang.Compiler.load(Compiler.java:7526)
	at clojure.lang.Compiler.loadFile(Compiler.java:7452)
	at clojure.main$load_script.invokeStatic(main.clj:278)
	at clojure.main$init_opt.invokeStatic(main.clj:280)
	at clojure.main$init_opt.invoke(main.clj:280)
	at clojure.main$initialize.invokeStatic(main.clj:311)
	at clojure.main$null_opt.invokeStatic(main.clj:345)
	at clojure.main$null_opt.invoke(main.clj:342)
	at clojure.main$main.invokeStatic(main.clj:424)
	at clojure.main$main.doInvoke(main.clj:387)
	at clojure.lang.RestFn.applyTo(RestFn.java:137)
	at clojure.lang.Var.applyTo(Var.java:702)
	at clojure.main.main(main.java:37)
Caused by: java.lang.ClassCastException: java.lang.String cannot be cast to clojure.lang.IFn
	at clojure.lang.Var.fn(Var.java:365)
	at clojure.lang.Var.invoke(Var.java:381)
	at clojure101.core$_main.invokeStatic(core.clj:7)
	at clojure101.core$_main.doInvoke(core.clj:4)
	at clojure.lang.RestFn.invoke(RestFn.java:397)
	at clojure.lang.Var.invoke(Var.java:377)
	at user$eval149.invokeStatic(form-init7051855349601256406.clj:1)
	at user$eval149.invoke(form-init7051855349601256406.clj:1)
	at clojure.lang.Compiler.eval(Compiler.java:7062)
	at clojure.lang.Compiler.eval(Compiler.java:7052)
	at clojure.lang.Compiler.load(Compiler.java:7514)
	... 12 more

as you can see value is displayed but after that exception is thrown.

I probably don't understand how functions/main work, so if you could point me... 😄

def should only be used at the top level (like where you have ns and defn)

functions have an implicit body and can take multiple expressions - you have them grouped in a set of parentheses

parentheses mean function invocation

so how would I save value that needs to be printed but takes value based on some logic?

so the def expression is getting evaluated, then the println, then you are trying to invoke the result of the def (a var) with the result of the println (nil). vars are invokable actually

use let here, not def

(defn -main
  [& args]
  (let [greting "Hello there"]
    (println greting)))

let creates locally scoped bindings

(defn -main
  [& args]
  (let [a 1
        b (+ a 1)]
    (println a b)))

let bindings can build on each other

thanks.

is there some good IDE that would give me syntax errors and similar for clojure?

right now I am writing code in Sublime Text, and manually running lein run.

the most popular are Emacs with CIDER (https://github.com/clojure-emacs/cider) or Intellij with Cursive (https://cursive-ide.com/)

Some others to consider are VS Code with Calva, or Atom with a variety of plugins (I'm not up on the latest there)

I use emacs but I think every editor is going to have some kind of basic setup to integrate with the clojure repl. That's the key, you want to start using the repl. So google sublime text clojure repl setup or something similar. Or if you want something more like Sublime Text but a little more popular for Clojure development look into Atom w/ Chlorine or Proto repl (I think it's called) or VS Code and Calva.

yup, what Alex said. haha

can you show me example of using def?

I've tried like this, still get Exception

(ns clojure101.core
  (:gen-class))

(def random-number (rand-int 11))

(defn -main
  "I don't do a whole lot ... yet."
  [& args]
  ((if (< random-number 5)
    (println (str random-number "Number is smaller than 5!"))
    (println (str random-number "Number is bigger than 5!")))))

It's because you have two open parentheses before the If

(defn -main

 "I don't do a whole lot ... yet."

 [& args]

 (if (< random-number 5)

   (println (str random-number "Number is smaller than 5!"))

   (println (str random-number "Number is bigger than 5!"))))

yes.

oops formating 😕

thanks.

😕

howd do you format code here?

I am not sure I understand you.

I would like to have the snippet of code I wrote to be formatted as code, the same as in your message

well you use `

before

and ` after the code

thanks

use triple backtics

that is for multiline code

for inline you use single

`

some code

Thanks 👍

@cvetan.simsic To get back to your problem, when you define a function like,

(defn example-fn 
  [arg1]
  (println arg1))

((some-fn arg1 arg2))

like

(defn closure
  [n]
  (fn []
     (+ n 1)))

thanks

👋 hello, I'm new here

I'm setting up codox, for generating documentation. In my project.clj I've configured it with :codox {:metadata {:doc/format :markdown}}

and ive tried writing by docstrings both as just regular docstrings and as the doc meta ` (defn foo [x] " Returns x" {x}) (defn foo [x] {:doc "Returns x"} {x}) ` But the docstrings and arguments arent added in my documentation. My namespaces are enumerated just fine.

Check the form for defn. I believe the docstring goes before the arg vector to disambigate the docstring from a value in the body of the function

oh, right

you are absolutely right, solved

thank you!

Hi! setting up Leiningen with shadow-cljs and having a bit of a headache

I can call shadow-cljs nicely with npm but it seems that invoking calls via lein fail, etc: lein run -m shadow.cljs.devtools.cli help produces just "Unknown action."

@theamazingekko did you try anything else but help? that action only happens to be implemented on the JS side 😉

ooooooohhhh!

compile etc should work fine

gotcha!

yeah it works xD

you may not want to use lein to run things as that does not work with the server mode

you can just configure :lein in shadow-cljs.edn and it will use lein to run things internally https://shadow-cljs.github.io/docs/UsersGuide.html#Leiningen

ah yes already changed that, if you mean adding that true -value? 🙂

yes

hmm.. I know the user manual is still work in progress but I think the help -command should be omitted from the examples. I know it was stupid of me not to try other commands but it kinda tripped me as it was the first step in testing calling commands from lein 😄

indeed 🙂 I'll fix that

no problem! thanks a bunch for the help though! Really looking forward to getting to know this tool 🙂

if you have questions come on by #shadow-cljs. I don't always notice questions here.

noted! thanks 🙂

how idiomatic is doing something like this

(def ^:dynamic add-acc)

(defn pipeline []
  (into [] 
    (map (fn [x] 
      (add-acc x)
      (inc x)) (range 10))))

(let [state (volatile! [])]
  (binding [add-acc (fn [x] (vswap! state conj (* 2 x)))]
    (pipeline)
    @state))

using an atom/volatile seems fine: https://clojure.org/reference/transducers#_transducers_with_reduction_state your example doesn’t seem to be really using transducers, though, just a regular map over a sequence. one thing to note is that a transducer might be lazy, in which case using binding probably is a bad idea

(into [] xform coll) is using a transducer, it is just an example tho

ah misread the parens 😅

I think the idiom is to use a higher-order function to create the stateful transducer

let me change the example a little

Hello! Trying to get Emacs+Cider going. I can open the repl buffer, and go into 'insert mode' and type stuff, but how do I get it to evaluate? 😛

ok, hitting return worked... but didn't before. sorry for the lame question.

(def ^:dynamic add-acc)

(defn pipeline []
  (into [] 
    (comp 
      (map (fn [x] (add-acc x)(inc x)))
      (map (fn [x] (add-acc 10) (dec x))))
    (range 10)))

(let [state (volatile! [])]
  (binding [add-acc (fn [x] (vswap! state conj (* 2 x)))]
    (pipeline)
    @state))

so i can't use a stateful transducer

sounds like what you need is reduce, not a transducer, unless I’m misunderstanding you