is there a way to remove nil keys from a record and not transform it into a map?

I am using:

(apply dissoc                                                                                            
       record                                                                                                  
       (for [[k v] record :when (nil? v)] k))

but the end result are maps instead of records

@iagwanderson You cannot remove any of the base keys from a record. Why do you want to do this?

After all, (some-key record) is going to be nil if some-key is not present or if some-key refers to a nil value.

I modeled a xlsx ROW to be a record because I have several operations that depend on the type and I wanted to clean the row at some point

I probably have to do this before converting the original map to the record, though

@iagwanderson Does the "type" depend on one field of the CSV? Maybe you want multimethods and a tagged hash map instead?

I multimethods

Hi there. I follow the book Web Development with Clojure 2nd Edition. But run into several problems. If I run lein migratus create guestbook like the book describes I get: https://paste.opensuse.org/view/raw/31a637a5

This is when I have {:user {:plugins [[luminus/lein-template "2.9.10.74"]]}} in the lein profiles file. Without that migratus doesnt even seem to be a task

Is there a distinction in naming conventions between transformation functions that may fail (and return nil) and transforms that throws on failure (I want to use the former with the keep collection function and the latter with map)? In F# for instance the former would likely be called try<whatever> like tryParseInt and return an Option.

Hi, I'm running into some problems trying out re-frame subscriptions. the commented line above works perfectly, but if I use the subscription version it doesn't work for some reason

this is how I initialized it in the db

only thing I could think of is maybe it has something to do with lazy eval? but I'm actually asking it to realize, so I'm quite lost

@shin can you post the definition of your :locales subscription

@danieleneal sure, here you go

Everything looks fine - although you can generally only dereference subscriptions within a render function, which may be where you’re going wrong

that line (def lcl (re-frame/subscribe [:locales]) is not intended usage

would be more like

(defn some-component []
  (let [locales @(re-frame/subscribe [:locales])]
    ... do something with locales)))

hmm, I'm using tempura (https://github.com/ptaoussanis/tempura) to play around with using different languages. you give it a list of locales and it will try to use them in the given order. I'm trying to subscribe to that, so I can change the order and thus language used or would you recommend any other way of doing that?

Hmm, various ways. The thing is once you have a subscription you can’t really go back to the land of normal function calls anymore. Dereferences are tracked and cause re-rerenders, and are cached, and when unmounted the cache is disposed, so there’s a fair amount of machinery involved.

This is why the partial is not working

One option would be to call tr with the locales each time you use it, seeing as you want the locales to be editable

(def tr (partial tp/tr {:dict my-dict}))

(defn some-component []
  (let [locales @(re-frame/subscribe [:locales])]
        text (tr locales [:text])]
    ... do something with text)))

There’s definitely other ways of arranging it though

I'll try it out at home, thanks very much! But is the way to do this I thought about sane or is there a better way to do things like that?

With re-frame, once you have subscriptions, you can build on them with more subscriptions, but you can’t pass a subscription to a normal functions in the place of a value. You can run a normal function on the de-referenced value of a subscription, because you now have an actual value - like (tr opts @locales @text)

the thing to remember is that subscriptions are objects whose dereferences are tracked so that components that dereference them re-render when the value changes

what is a quick and simple way of testing if my function actually returns a lazy seq, instead of killing a restarting the repl each time it starts evaluating an infinite seq?

You could do something like this:

(defn lazy-seq? [coll]
  (= (class coll) clojure.lang.LazySeq))
=> #'user/lazy-seq?
(lazy-seq? (for [x (range 10)] x))
=> true

@sakalli Also if you wanna peek into the infinite seq, try https://github.com/borkdude/finitize

thanks both 🙏

@sakalli Another useful trick is to (set! *print-length* 100) in the REPL. This will prevent lockup if an infinite sequence is printed.

Where is the proper place to put a doc string within defmulti and defmethod

after the name of the defmulti, and defmethod shouldn't require its own

if you have (defmulti foo "get a foo from the arg" ...) (defmethod foo :bar ...) how would you even ask for the method's doc other than getting the one for the multi?

a defmulti creates a var, those carry docstrings, a defmethod alters the multi, it doesn't have its own var to put doc on, or ask doc from

hi all! mega beginner here, i'm doing this (https://practicalli.github.io/clojure-webapps) practicalli tutorial, and when I try to run the repl with lein repl I get this error, couldn't find any usefull info online

Caused by: java.lang.NoClassDefFoundError: IllegalName: todo_list.core/_dev_main.proxy$java.lang.Object$SignalHandler$d8c00ec7
        at java.lang.ClassLoader.preDefineClass(ClassLoader.java:654)
        at java.lang.ClassLoader.defineClass(ClassLoader.java:761)
        at java.lang.ClassLoader.defineClass(ClassLoader.java:642)

is there a file src/todo_list/core.clj which contains something like (def -dev-main (proxy ....))

yup

the project runs, but not the repl

(defn -dev-main
  "A very simple web server using Ring & Jetty that reloads code changes via the development profile of Leiningen"
  [port-number]
  (jetty/run-jetty (wrap-reload #'app)
     {:port (Integer. port-number)}))

hmm - I'd try running lein clean then starting the repl again

when I use (require) in the repl, is the :all implied (Compared to doing (ns myns (:require randomlib :refer :all))?

no options are implied

:refer :all should only rarely be used (there's an annoying thing where all the lib README files seem to show it in their examples...)

no luck, I'm on WSL btw, could this have anything to do?

I'm in a use case where I actually need all the functions in the file.

you can always call all the functions, the normal way to do this is via :as

(and there's no name conflict)

OK - use :refer :all if it's appropriate, just know it's not considered normal

the normal thing is (require '[clojure.set :as set]) then you can use (set/union ...) (set/intersection ...) etc.

well, :all isn't actually an option for (require) (unlike :require as part of a (ns) call).

it is

require as used alone is exactly the same function that ns calls

and has the same options (once you sort out the quoting differences outside a macro)

oh weird. ok. I see that in the doc now. It threw an exception at me.

(ins)user=> (require '[clojure.set :refer :all])
nil
(cmd)user=> (union #{:a} #{:a :b :c})
#{:c :b :a}

ty! I forgot/didn't know I needed the '[].

it's the same as in the ns form in that respect

What does the ' do here? The code I'm working with doesn't have that in the (ns) declaration.

that's what I meant by has the same options (once you sort out the quoting differences outside a macro)

' means "don't evaluate this form"

so symbols are used as is and are not resolved, and function calls are just lists

Ok, so is the ' optional (and included for best performance)?

it prevents an error clojure.set isn't bound

it's the symbolic name of something you want to load

you'd get a syntax error if you used it unquoted

ok

Why do we not need it in:

(ns myns
  (:require [otherns :refer :all]))

the ns form is a macro, and it doesn't try to evaluate the symbols you put in the require form

macros can decide when something is evaluated or not

ah, gotcha

when you call a function (eg. require) the args are evaluated first, then passed to the functio

so ns, being a macro doesn't actually itself evaluate anything anyway, unlike (require) which is a function and will evaluate immediately.

when you call a macro (eg. ns) the args are passed as a list of symbols and input literals and the macro decides what to do with them

right

I mean a macro usually does evaluate things (clojure macros can use the entire clojure language as needed), but they usually just turn one list (form) into another then return it to be compiled

ty very much for the explanation!

What benefits do we have using ClojureScript for server side instead of Clojure?

some people are trying to do something that is easier to do in a js vm rather than jvm

or are OK with losing performance in exchange for faster startup

Looking to generate some documentation for some website back and front end stuff. I'd like to be able to autogenerate or with some massaging generating dependency/flow diagrams. I know codox is common for pulling docs together, but I didn't see any dependency graph makers. This is what I'm thinking. Any recommendations?

Should one prefer tagging fns ^:private to using defn-? (question spurred by https://groups.google.com/forum/#!msg/clojure/zaWlDbOhKCM/sD_iOM_k9WcJ)

there is a third way

what is the third way?

don't use either

that's fair i guess. personally i think a project is easier to understand if you're clear about what's used only within a namespace

a google search yields a split internet, use w/e makes your team happy I'd say (my personal opinion would be explicitly using ^:private since a good IDE will provide auto-completion and this is more consistent with def not having a matching def-)

Hello everyone. I have a doubt regarding Clojure and i couldn’t find a clear answer. Assume i have a bank account with the balance of $100.00 I then receive 2000 request to withdraw these $100.00, usually on a Java code, you would need to lock the resource as soon as the first request arrives, so that only the first one can be made and all the others shall fail. I saw examples using the actor model were you can use a single actor to represent one account, and so the 2000 requests would be made by the account actor, leading to the expected result Does Clojure have any way on helping with this? I saw about the agents but i couldn’t find any information that i could digest on this.

@pedrommrabello agents are a straightforward way to do something much like an actor, the important difference being that an actor is a method that you send data to, and an agent is data you send a function to

but you can set a validator, so that the action won't succeed if it leaves a balance below 0 for example

you can also do this with atoms, which are much more intuitive to use

Wouldn't this be an excellent case of storing the value in an atom? Hmm, I suppose that doesn't work for multiple processes?

nvm, you beat me to it.

with multiple processes you need inter-process communication which clojure doesn't offer out of the box (unless you meant threads, and threads are why we need things like agents, atoms)

No, I meant processes since they don't share memory.

right, in that case nothing in clojure really helps - you'd want some IPC strategy, clojure doesn't really cover it

Sorry, still learning multi-process. What is IPC?

inter-process-communication

@pedrommrabello any reason this isn't handled by a database with ACID semantics?

right, it's also IPC if you ever reboot your VM (two processes, at different times, working on the same data world)

you can use refs to coordinate multiple stateful changes https://clojure.org/reference/refs

Hey guys, I can't figure out what I'm doing wrong here:

(deftest funcmocktest
  (testing "mock a func"
    (with-redefs-fn {#'clojuretesting.secondnamespace/myfunc (fn [] (print "This is a mock."))}
      (is (= nil (clojuretesting.core/mysecondfuncwrapper))))))