hi guys

I'm a bit lost with namespaced keywords

given I'm in a namespace foo.bar, ::a should evaluate to :foo.bar/a

what if I want to reference :foo.bar/a from foo.baz?

then you use :foo.bar/a or you can alias foo.bar to bar and use ::bar/a

alias is usually done via the :as key in require

oh, cool

what's the advantage of using ::bar/a instead of :foo.bar/a?

Clojure 1.9.0-RC2
(ins)user=> (ns foo.bar)
nil
(ins)foo.bar=> ::a
:foo.bar/a
(ins)foo.bar=> (ns foo.baz (:require [foo.bar :as b]))
nil
(ins)foo.baz=> ::b/a
:foo.bar/a

it’s more succinct

I see

thanks a mil @noisesmith

Hi guys, How mostly do you guys do your function tests? If there are moving parts, for example calling another function which query a database, making the function "impure", do you guys have some kind of convention to "inject" the parts into the parent function? For now I'm doing something like:

(defn register
  ([user create-fn]
   (if-let [new-user (create-fn user)]
     {:type :created :message (dissoc new-user :password)}
     {:type :error :message {:error "failed to register user"}}))
  ([user]
   (register user u/create)))

So based on the function above, I inject a mocked function when testing, a function that immediately returns value just for the sake of testing the parent function.

So this maybe something that's asked quite a lot here, but I'll ask anyway. I find myself interested in clojure, I was interested in LISP some time back but never got the chance to use it. Now that I'm doing more web stuff (Doing django at my work atm), I started to read about clojurescript. It's been a couple of weeks and I see so many libraries and frameworks and comparisons between each other that I'm literally frozen by too many choices - it's debilitating. I only can do clojurescript in my spare time and that spare time is a bit hard to come by these days with all the other stuff in my life. To start with, I'm not a genius coder by any stretch of the imagination so I can't 'grok' a framework or a language in two afternoon. With all this, I go read abour reagent, re-frame, Fulcro, Keechma, Om next, etc. And there are so many blog posts detailing why one of these is better than the others. I started trying out re-frame once, tried Fulcro also. But for me this takes time. I am an intermediate level coder who'd like to just learn something useful and perhaps fun. I don't want to put a lot of effort into learning something (Doing a personal project with it say,) and learn later that that framework is abandoned. It seems there's so many stuff around at the moment that it's implausible to think that they all will survive for long. But if you look at other languages, they have either one or two well respected ways of doing something. So, what would be my safest bet? Any suggestions are welcome.

clojure’s fun, plus it’s JVM so useful beyond just hacking around 🙂

when I'm picking a tool, I usually go look at the options on https://www.clojure-toolbox.com/ and pick a project that seems well-established

oh i see, i got confused by the post.

@duminda having spent the last year playing with om.next and clojurescript, i'm currently evaluating rum and it's really good. i'm not sure what sort of web dev you're working on. my needs are: realtime server-> client and client -> server comms for which I use sente. beyond that, my current recommendation would be rum. i'm just getting started with datascript, which is like a clientside db that looks like datomic syntax. Check out this post and see if you're building something that would benefit from this model / approach. http://tonsky.me/blog/the-web-after-tomorrow/

@hawari.rahman17 i'm curious about this too. making fake inputs to test database grabs seems like a decent way to get about it.

Yup @sova, as of now it's decent enough to get by. But I still kinda have a feeling I'm missing out on something here. 😆

Hey all, I'm really confused about core.async

Can someone help me understand why this doesn't return "Hello World"?

http://app.klipse.tech/?cljs_in=(ns%20demo.core%0A%20%20(%3Arequire-macros%20%5Bcljs.core.async.macros%20%3Arefer%20%5Bgo%20go-loop%5D%5D)%0A%20%20(%3Arequire%20%5Bgoog.dom%20%3Aas%20dom%5D%0A%20%20%20%20%20%20%20%20%20%20%20%20%5Bgoog.events%20%3Aas%20events%5D%0A%20%20%20%20%20%20%20%20%20%20%20%20%5Bcljs.core.async%20%3Arefer%20%5Bput!%20chan%20%3C!%20%3E!%20timeout%20close!%5D%5D))%0A%0A(def%20a-channel%20(chan%201))%0A%0A(go%0A%0A(%3E!%20a-channel%20%22Hello%2C%20world!%22)%0A%0A(%3C!%20a-channel)%0A%20%20%0A%20%20a-channel)

@derpocious A few problems: On line 13, you're taken the "Hello Word" out of the channel and discarded it. On line 15 you returned an empty channel instead of "Hello World". go also returns a channel so you must take from the channel returned by the go block

Since Klipse runs on CLJS in the browser, you can't take from the channel synchronously. This will work in Klipse:

(def a-channel (chan 1))
(put! a-channel "Hello World")
(take! a-channel println)

Thanks.

But why is it (take! a-channel println) instead of (println (take! a-channel))

take! is async, it calls a function when it's able to take a value off the channel

it's not possible to wait for a value synchronously in JavaScript land 😉

in Java you can do this: (println (<!! a-channel))

Hmm I thought <! was also async take a value off of a channel

<! is only available in a go block

look at it's source 🙂 (source <!)

thanks. I need I need to require source. Does it work in cljs?

what's the best way to find the import for cljs?

For example, take! just causes my code to break and googling "cljs take!" doesn't seem to give me the answer

so trying to implement a nightly email job for a web app. would it be recommended to run it in a separate process from the web request it gets triggered by? if so, is there a simple way to do that. or need core-async

i think i read each method implements runnable, so probably not.

There are a lot of variables to consider when answering that question. Is your web service process currently a singleton? Likely to remain that way? Must your job be run by only one process? Do startup time or other operational considerations suggest adding other processes is a pita?

is it possible to rollback a transaction created inside a dosync call on purpose and without having to throw an exception?

shouldn’t anything that rolls back a transaction throw an exception to the caller? otherwise I’d expect strange and very hard to find bugs

i'd like to rollback in the context of unit tests, but you have a point

maybe i should stick to using bindings over those ref values

if throwing an exception to the caller is OK, but you don’t want to create one artificially you could call (io!) maybe?

or make the ref something that is passed in explicitly, so you can create fresh ones explicitly for each test

that’s often a good pattern, making all mutable resources (refs would count as a mutable resource) be arguments rather than namespace level globals

a compromise is to accept an explicit resource arg, and default to the global

that way at least your tests can be sane

i'm doing the opposite of that, i have them defined as namespace level globals, then on my unit tests i'm binding them to another value

right, that’s the thing that causes problems and the thing I’m saying maybe not do

in particular, since the use case for refs is for things where performance concerns mean you want to reduce contention and coordinate acting on N items - that’s often a case where you want a collection of refs and that gets inconvenient with globals

i decided to do it like that because i'm using them in multimethods, it seemed to make more sense, but i'll see if i can work on a refactor

derpocious Hey all, I'm really confused about core.async Can someone help me understand why this doesn't return "Hello World"? http://app.klipse.tech/?cljs_in=(ns%20demo.core%0A%20%20(%3Arequire-macros%20%5Bcljs.core.async.macros%20%3Arefer%20%5Bgo%20go-loop%5D%5D)%0A%20%20(%3Arequire%20%5Bgoog.dom%20%3Aas%20dom%5D%0A%20%20%20%20%20%20%20%20%20%20%20%20%5Bgoog.events%20%3Aas%20events%5D%0A%20%20%20%20%20%20%20%20%20%20%20%20%5Bcljs.core.async%20%3Arefer%20%5Bput!%20chan%20%3C!%20%3E!%20timeout%20close!%5D%5D))%0A%0A(def%20a-channel%20(chan%201))%0A%0A(go%0A%0A(%3E!%20a-channel%20%22Hello%2C%20world!%22)%0A%0A(%3C!%20a-channel)%0A%20%20%0A%20%20a-channel)

you never print it

replace (<! a-channel) with (println (<! a-channel)) if that's all you want

a-channel is a channel

which is why at the bottom it's saying ManyToManyChannel

hello, anyone knows why the clj executable doesn't return anything?

I've installed rlwrap already

I hoped in the tutorial to open the repl

I've used the bash installer

using linux mint latest

so it just silently exits?

@noisesmith yes

@vinnyataide You need to install Leiningen: https://leiningen.org/#install That's the easiest way, then you can run lein repl.

I think I found the problem

I have no java

It's a brand new

@ghsgd2 that’s an alternative but the clj tool is totally different

It should check and warns doesnt it?

@vinnyataide haha that would do it

So that remains as a future feature haha

@vinnyataide yeah that would be worth a PR or jira ticket I bet

can I do it? or would I need to call someone?

you can make a PR or jira ticket - anyone can make a jira tiket, you need to sign up an online contributor agreement or they won’t look at a patch though

ok thanks

@vinnyataide either way you would start around here https://dev.clojure.org/jira/secure/QuickSearch.jspa

will do! just a heads up a default-jre install solved it

:thumbsup:

Hello everyone, recently I started with a book called web-development-clojure v2 The libraries it uses changed slightly, according to the book I need to connect to repl and run a query on the db That is what I have:

user=> (use 'guestbook.db.core)
nil
user=> (get-
get-in get-messages get-method
get-proxy-class get-thread-bindings get-validator
user=> (get-messages)

IllegalArgumentException db-spec mount.core.DerefableState@61222e9e is missing a required parameter clojure.java.jdbc/get-connection (jdbc.clj:379)

(ns guestbook.db.core
  (:require
    [clj-time.jdbc]
    [conman.core :as conman]
    [mount.core :refer [defstate]]
    [guestbook.config :refer [env]]))

(defstate ^:dynamic *db*
           :start (conman/connect! {:jdbc-url (env :database-url)})
           :stop (conman/disconnect! *db*))

(conman/bind-connection *db* "sql/queries.sql")

-- :name save-message!
-- :doc creates a new message
INSERT INTO guestbook
(name, message, timestamp)
VALUES (:name, :message, :timestamp)

-- :name get-messages
-- :doc selects all availible messages
SELECT * from guestbook

@janis.urbis Does the book tell you which versions of the libraries to use? (in your project.clj I expect)

If you change the versions from what's in the book, you will run into incompatibilities between the libraries.

@seancorfield no, it's just says use luminus

so it's scaffolded project with only one change

Thanks @chris!

I changed migration to what book requires

CREATE TABLE guestbook
(id INTEGER PRIMARY KEY AUTO_INCREMENT,
name VARCHAR(30),
message VARCHAR(200),
timestamp TIMESTAMP);

It is possible for me to return the value that was in the channel instead of just printing it?

@janis.urbis How did the book tell you to create the project?

lein new luminus guestbook +h2

The author @yogthos is on this Slack but not in #beginners -- I'll invite him in

@yogthos wondering if you can help @janis.urbis as he's trying to follow the guestbook example in your book?

hi sure

@janis.urbis the error you’re seeing means that the database state hasn’t been started yet

mount uses namespace hierarchy to resolve the resource loading order, and if a namespace isn’t included anywhere, then the resources in that namespace won’t be loaded automatically

to load the resource by hand you just have to run (mount.core/start #'guestbook.db.core/*db*) in the REPL

@janis.urbis try running (mount/start #'database) in the repl and run the query again

neeeevermind… lol

🙂

Welp, my work is done here boys!

hehe

(sometimes there's so much "magic" in these Leiningen templates that they're not the easiest way for beginners to learn Clojure!)

@yogthos wow, thank you for the detailed explanation) it works now)

yeah there are definitely some gotchas

I do try to keep luminus as simple as practical

@admay @seancorfield thank you for the help too 🙂