Hello everyone! I’m starting to work with clojure, and I’m having some questions about project organization, I have a project with compojure and monger, how to you usually organize the files? How do I handle the database connection among the application? Do I have to connect on every request or do I connect on application start and reuse the connection?

Hello you all 🙂 I am JUST starting with clojure and i'm just doing a simple test to try and write to a .txt file: (defn write-to-file [] (`slurp "file.txt" "test123"))` (`write-to-file)` I get the error

(slurp "file.txt" "test123"))
       ^--- Use of undeclared Var tallex.time-dive/slurp

@carl.waerner How are you running that code? In a REPL? Where did tallex.time-dive come into that code?

hello, I am trying to take this code and do something similar in clojurescript: https://github.com/joinr/spectest/blob/master/src/spectest/core.clj

but I have errors that clj-kondo can't resolve the symbols.

Also, I am not totally sure if I am requiring the correct libraries

Here is my code with the defn-spec parts highlighted. https://github.com/JimLynchCodes/Programming-Jokes-Generator/blob/master/src/main/clojurescript/serverless/functions.cljs#L62_L68

@seancorfield I took your advice of trying to use spec instead of schema, but I would like to try to use the orchestra "defn-spec"

I've never looked at Orchestra.

(and I don't do anything with ClojureScript)

I had asked about this on reddit, and someone wrote this for me: https://github.com/joinr/spectest/blob/master/src/spectest/core.clj

It seems to me like a nice way to putting the spec right into the function definition

https://github.com/joinr/spectest/blob/master/src/spectest/core.clj#L75

I get the impression some sort of combined spec/defn thing is going to be part of Spec 2, based on what Alex has been saying. Rich is deep in thought about function specs for Spec 2. So I'm waiting until that drops since it'll be standard and built-in.

In the meantime, I'm sticking to plain Spec 1.

So, random morning thought. TypeScript, Python types on the rise... specs in Clojure. Is it a trend? For now? Will it pass? What does it say, if anything? :face_with_monocle:

@derpocious You can use a configuration to make errors around orchestra.core/defn-spec disappear. See last note here https://github.com/borkdude/clj-kondo/releases/tag/v2020.01.10

I'm having a bit of difficultly understanding core.cache. What I'm trying to do appears very simple (in fact, just following the wiki), yet the results are not what I expect

(require '[clojure.core.cache :as cache])
(def C (cache/ttl-cache-factory {} :ttl 5000))
(-> C (assoc :a "Hello World"))
(:a C)

the result of evaluting (:a C) is nil.

pretty much a 1:1 from here

aaaah

of course

the structures are immutable

Hi! I'm looking for something like maplist in Common Lisp:

(maplist (lambda (x) x) '(1 2 3 4))
→ ((1 2 3 4) (2 3 4) (3 4) (4))

(take-while seq (iterate next ...))

You might find reductions to be a useful tool here, maybe with pop

I would like to store a sample of the arguments and the image from functions that are called during a test run, such that I could run regression test afterwards. Is there a library that already provide such functionality? I am thinking of a non intrusive library (that is one that would perform alter-var-root

and wrap functions from some namespace with the right behavior?

The goal would be to log the arguments that are run during the program to make regression test during libraries updates.

Hello 🙂 I am reading Programming Clojure and am following along the chapter on spec. I ran into a bit of a problem which I don't fully understand. Trying to execute the following code returns me a Runtime Exception Invalid token: ::music/id ...

(s/def ::music/id uuid?)
(s/def ::music/artist string?)
(s/def ::music/title string?)
(s/def ::music/date inst?)

(s/def ::music/release
  (s/keys :req [::music/id]
          :opt [::music/artist
                ::music/title
                ::music/date]))

@jakob.durstberger it means auto -resolve the alias music so I wonder if you don't have a namespace required with that alias?

@seancorfield yeah, I definitely don't have a namespace music. The book mentions auto-resolving namespaces a few pages earlier but I haven't fully understood them yet. At least now I know what I have to search for / re-read. Thank you 🙂

This is a bug in the book - should either be : or define the alias

There was a period in 1.9 pre releases where this did work and I think this code may have been checked during that time, then not checked at release time

Which would look more like "good" Clojure code?

Either is fine

Sometimes I think heavy use of threading compromises the readability, are both really fine? @alexmiller

@zignd They are not quite equivalent, I think? In the first one you have (apply (resolve-controller operation) operation) and in the second you have ((resolve-controller operation) operation) -- apply treats the last argument as a sequence (of arguments) in the call. Assuming the controller function takes a single argument, I think the first form would need (apply [operation]) so that the semantics match.

And that apply would make me want to use the second form instead.

Or I might use (as-> f (f operation)) instead of (apply [operation])

You're correct @seancorfield! After a few iterations not understanding what was going wrong I realized I was not using apply correctly. But thanks for noticing that and telling me xD

(let [operation (adapters/from-json-to-map line)]
    (-> operation
      (resolve-controller)
      (apply [operation])
      (adapters/from-map-to-json)
      (println)))

This is the current state of that code xD

(-> line
    (adapters/from-json-to-map)
    (as-> op ((resolve-controller op) op))
    (adapters/from-map-to-json)
    (println))

That indeed looks pretty :thinking_face:

Yes, as-> is designed to be used in a -> pipeline to provide a binding, to be used in an expression where the item being threaded is neither the first argument nor the last argument.

Interesting! I'm going to change to that! Thanks @seancorfield!

You can also put ->> into a -> pipeline for any subset that needs to be "last argument" as opposed to "first argument" threaded, but some people consider that a code smell and an indication that you're switching between thing/collection and sequence so you should refactor into smaller functions.

https://stuartsierra.com/2018/07/06/threading-with-style

and https://stuartsierra.com/2018/07/15/clojure-donts-thread-as

(there are lots of good pieces of advice in that blog series -- although not all of them are considered universally good style in Clojure)

Nice! I'll make sure to read them, might enlighten me in new possibilities with the threading macro. This one you showed me with the as-> is really clever tho, I don't that would come to my mind hahahah

To give you an idea of usage, we have 32 instances of as-> in 19 files, out of a 90,000 line codebase.