Clojurians Log v2

anyone know of any good documentation on how deps.edn works?

i don't mind reading the code either

but not sure where it lives

https://clojure.org/reference/deps_and_cli

thanks

@brandon.n.atkinson there's a link in the above, but https://clojure.org/reference/dep_expansion for more gory details

Any options on using a var binding as a require arg, instead of a literal?

like this?

(let [str 'clojure.string]
  (require str))

do you have an example of what you're trying to do?

(def config {:namespace "clojure.string"})
(let [n (:namespace config)]
  (when (n) (:require [n :as module])))

n is a var, require wants a list/vec of literals

n is "local" not a var

not sure what you're actually trying to do, but requiring-resolve might help

fwiw, the following works:

(let [config {:namespace "clojure.string"}
      n (:namespace config)]
  (when n (require [(symbol n) :as 'module])))
(module/lower-case "CLOJURE")

thanks for the feedback

im looking for behavior parity between an existing python code base and what can be accomplished here. The python project leverages importlib and dynamic loading in a fashion somewhat similar to java spring ioc, interfaces, and varying implementations.

repl testing looks as if requiring-resolve can provide at least the edn config ->conditional import path here.

Is there a preferred way to add support for multiple languages? For example, use maps like {:en "Hello, World", :de "Hallo Welt!", etc...} instead of strings and then let the display function choose depending on chosen language?

Any suggestions as to why (<http://clojure.java.io/resource|clojure.java.io/resource> "config.edn") is returning nil even though the config.edn file is on the classpath, as shown by lein classpath command? Its an older Clojure project with Leiningen. I tried using Java 8 and Java 11, a few different versions of Leiningen. I can slurp the file...

Is there a way to see the classpath from the REPL ??

I have tried some variations around this example, https://gist.github.com/ekoontz/1502838 but I get nil returned. I though the code wasnt working, but perhaps Leiningen is not correctly setting the classpath for the repl, which would explain the issue

@julian608 In case you're not familiar with this domain, you can find a plethora of stuff to read about searching for internationalization and localization (abbreviated as i18n and l10n ). There is a lot of nuance to doing this well at scale. But if you're just looking for something quick to get you started grab an existing i18n library (e.g. https://github.com/ptaoussanis/tempura) and try not to go down the rabbit hole of learning everything about this - the well runs very deep. :)

Curious that this code returns the leiningen jar as the class path, rather than the really long classpath I get when using lein classpath command

(doseq [url (seq (.getURLs (java.lang.ClassLoader/getSystemClassLoader)))]
       (println (.getFile url)))

What I use most often is cider-open-classpath-entry There's also a system property for this:

(System/getProperty "java.class.path")

That looks nice, thanks!

I load a few files using io/resource, they all are in the resources folder

Definitely something in the Leiningen project messing up the classpath when running the repl either on the terminal or via the editor. I think Leiningen has been silently failing to build the classpath. Also it seems Leinigen was not downloading all dependencies.

(defn my-fn [{:keys [unparam1 unparam2]
              :param/keys [param1 param2 param3]
              param-type :param/type
              :as params}]
...)

Hmm, this just shows the leiningen jar as the class path. very strange.

I can use io/resources in a newly created project. There is something strange in this legacy project that is messing with the class path I think.

It works fine for me. I’ve been using it for a long time from jdk 8 to jdk 16. Note that your code fails completely on modern JDKs

Just in case: it’s always good to try lein clean if you experience weird issues

try lein with-profile +repl cp to get the classpath a repl would use

you can swap in other profiles of course

also for io/resource to work, the document shouldn't be on classpath, its parent folder or zip file / other container should be

nb. "." shouldn't be on classpath, you should have specific subdirectories of the project like src and resources that are on classpath

if it was "failing to build a class path" java wouldn't even be able to run anything. what is happening is you are asking for a different classpath than you think you are.

> it seems Leinigen was not downloading all dependencies. that makes me think that something replaced the classpath / dep vector where it should have been adding to it (look for the ^:replace metadata in a profile for example)

Yes, the code does work correctly in a new project. It gives the leinigen path in the older project, I think because something is failing... Thanks.

Hey everyone, is there a concept of a spread operator in Clojure? I want to merge a map with a sequence of maps, but I want to 'spread' out that sequence.

apply

The project does something intricate with project.clj and profiles.clj (which is also in the root of the project). I commented out all the bits I didnt understand and at least I have a proper class path now. I also decided to add a deps.edn file and use Clojure CLI tools. This showed some issues with transitive dependencies which I've now resolved.

Hi, I was wondering if there was any way of making some simple dfs traversal work with recur? I understood that recur uses tail optimisation which is not otherwise possible given the JVM. Now , if I simply replace my recursive call to dfs, I get an error 'Can only recur from tail position'. Is there a clojurian way of making this sort of code work with tail optimisation? Thank you very much for your help. (*fn* dfs [tree traversed] (*let* [node (first tree) c1 (second tree) c2 (nth tree 2)] (*if* (nil? tree) (conj traversed tree) (concat [node] (dfs c1 traversed) (dfs c2 traversed)))))

in order to tail recur over a tree you need to lift the rest of the tree traversal into a data structure, which leads to harder to read code. except when you have extreme efficiency needs, the right thing to do is just consume stack proportional to the tree size

by simple non-optimized self call

also your lazy structure via putting the self call inside concat already prevents stack usage explosion I think?

I think typical default max JVM stack depth is on the order of a few thousand calls (it can be configured larger when you start the JVM via command line options). If you expect the DFS to traverse more nodes than that at maximum depth, then you should consider whether you might want to use a method that manages the DFS control flow via a data structure, vs. consuming call stack.

hi team, I am facing this issue during deployment after changing java10 to 11 version. I also added JAXB library but the issue is still there. any suggestion? can this be related to the leiningen version as well?

you find yourself in a twisty maze of passages, all alike

you are building an uberjar, and if you find the file named module-info.java in the uberjar and remove it, then maybe that will fix things

you can maybe use this https://github.com/technomancy/leiningen/blob/master/sample.project.clj#L422 to do it automatically

not 100%, but my guess is some dependency you are pulling in includes some java module stuff, and that is all be blindly shoveled into the uberjar by lein, so then java now thinks your uberjar is a java module thing, which makes things weird

For anyone who’s perused https://www.manning.com/books/the-joy-of-clojure-second-edition?gclid=CjwKCAjwy42FBhB2EiwAJY0yQlgELvVtu7ErEKP-G0m9lqeWm4wS0BInny8yz1tHUxVM4gALeSBVohoCXVIQAvD_BwE, I was re-reading a section this morning and hit a point of confusion. In 8.1.1, there’s a quick review of syntax-quote, unquote, and splicing, with the example function contextual-eval:

(defn contextual-eval [ctx expr]
  (eval
   `(let [~@(mapcat (fn [[k v]] [k `'~v]) ctx)]
      ~expr)))

(defn contextual-eval [ctx exp]
    (eval `(let [~@(mapcat (fn [[k v]] [k v]) ctx)]
       ~exp)))

(contextual-eval '{a 1 b 2} '(+ a b)) ; 3
(contextual-eval '{a 1 b 2} '(let [b 1000] (+ a b))) ; 1001

I'm not sure I would write it the same as their example, but there's a difference in behavior. Eg:

(defn contextual-eval [ctx expr]
  (eval
   `(let [~@(mapcat (fn [[k v]] [k `'~v]) ctx)]
      ~expr)))


(defn contextual-eval-mead [ctx exp]
    (eval `(let [~@(mapcat (fn [[k v]] [k v]) ctx)]
             ~exp)))

(contextual-eval '{a (+ 0 1) b 2} '(+ a b)) ;; exception
(contextual-eval-mead '{a (+ 0 1) b 2} '(+ a b)) ;; 3

Thank you folks

I haven't read the book and maybe it makes sense for their example, but calling eval in a macro seems super weird to me

Oh it’s not a macro yet — just a regular fn being used to introduce the concept of macros

ohhh, right. duh. nvmd :homerdisappear:

Thanks for your response earlier, walking through it now

it's a little easier to see what's going on if you just show the code being passed to eval:

(defn contextual-eval-form [ctx expr]
  (let [form `(let [~@(mapcat (fn [[k v]] [k `'~v]) ctx)]
                ~expr)]
    form))

(defn contextual-eval-mead-form [ctx exp]
  (let [form `(let [~@(mapcat (fn [[k v]] [k v]) ctx)]
                ~exp)]
    form))

(contextual-eval-form '{a (+ 0 1) b 2} '(+ a b))
;; (clojure.core/let [a '(+ 0 1) b '2] (+ a b))

(contextual-eval-mead-form '{a (+ 0 1) b 2} '(+ a b))
;; (clojure.core/let [a (+ 0 1) b 2] (+ a b))

It makes sense why the book version breaks, but I’m still confused as to why it might be the preferred/idiomatic version vs. the simpler one. Trying to think of an example where contextual-eval-mead would be worse…

well, for the purposes of introducing macros, their version is closer to how a macro works

a macro gets unevaluated forms which is what their version is doing

ah ok. maybe that’s the use of having it in there then.

thanks

I recently came across a use of this in the malli codebase: https://github.com/metosin/malli/blob/master/src/malli/core.cljc#L1969

I usually would write that as:

(list 'quote (symbol (str name)))

interesting, it's good to have the comparison - thanks!

the '~` idiom is a neat trick though. Might be worth getting used to.

I'm working my way through The Reasoned Schemer using core.logic and I'm having some trouble with the nevero goal defined in Chapter 6 frame 14:

(defrel (nevero)
  (nevero))

(defn nevero [] (nevero))

(run 1 q
  #u
  (nevero))

(run 1 [q] u# (nevero))

Hello! I'm 9 days into learning Clojure. How do you all approach solving problems?

For an in-depth look at problem solving techniques, G. Polya's "How to Solve It" is great, http://www.math.utah.edu/~pa/math/polya.html

The overview is a good starting point: 1. Understanding the problem 2. Devising a plan 3. Carrying out the plan 4. Looking back (eg. testing)

there has to be a better and safer way than (keyword (str "example." (name :foo)) "bar") (with :foo coming from a parameter). to give more context, I want to put all item names for my game into that dictionary, nested under :item - so for example :item {:sword {:name "Sword", :description "A Sword with a sharp blade."}} and when outputting the name of the item, I would have :sword and want to call tr with :item.sword/name - is this a valid approach or should I rethink it?

I have two files/namespaces that alias two different namespaces with the same symbol and I’m getting an alias conflict error. Why can’t I use the same-symbol (`:as some-symbol` ) when referring to two different namespaces in two different files?

// one.clj
(ns com.app.one
  (:require [com.app.models.one :as model]))

// two.clj
(ns com.app.two
  (:require [com.app.models.two :as model]))

looks ok to me. Maybe it's some other issue. What's the error you're getting? What's the symbol alias you're trying to use?

1. Caused by java.lang.IllegalStateException
   Alias model already exists in namespace
   neuromancer.core.pay.invoice, aliasing
   neuromancer.models.pay.account

If I change the alias for one of them, it compiles w/o error

is there another require in the same namespace using model?

what do you mean by compile?

using cider’s hot key C-c c-k to compile the current namespace

and no I just have 3 requires in this namespace, only one aliasing :as model

ah, I'm guessing there's some persistent state which won't let you change it

you can either restart your repl or run

(ns-unalias *ns* 'model)

for each namespace before trying again

Cool let me give that a shot

there's probably a better way to reload each namespace without restarting the repl, but my repl workflow is fairly basic

Yeah there’s something weird going on with my repl. I restarted it, and it stopped giving me that error, but now It’s giving some other error that also looks like a caching problem

progress!

Ah nah figured it out, now everything’s compiling! just needed to restart the repl, thank you 🙂